I do apologize for putting words in your mouth, but you seem to be avoiding answering the simple question, did you try to tune your TBI combo? If not, then you really don’t understand the system, and judging by your carbs are simpler so their better comments confirm this further.

So the we’re all stupid comment was a bit of a stretch, but your comments do insult what we’re doing here. I know you didn’t do any research or you would have known that TBI won’t limit a sub 400 HP motor. As far as I can read, you never said TBI had any strong points, you only pointed out its weaknesses, which you are misinformed about. Also Fast didn’t agree with your limits, actually he spent several post trying to educate you on what the real limits were and the actual capabilities of the system.

Finally, TPI is not a better FI system for your said reasons. In fact TPI is proven to restrict even a stock L98 (stealth ram frees up all kinds of top end power). The ecm doesn’t have more tuning capabilities, actually the TBI ecm is more thoroughly hacked out and understood, and we’ll very soon have a new add on board that will put the lowly TBI ecm a notch above all factory ecm’s and some aftermarket. Most serious tuners ditch MAF and go SD for a reason, the reason is you actually have more control of your AFR and it gets one more restriction out of the intake tract. The only real advantage of a MPI system of any kind is that it gets fuel flow out of the runners and allows the use of widely available injectors and TB’s. Of course you already know this without ever burning a chip or spending any real time with FI of any kind, or have you? You never did say.

I guess I’m so defensive because your obviously “not from around here” and are spouting off wrong information. Carburetion is fine and dandy, I ran one for years. If simplicity is on the top of your shopping list, then it’s your only option, just don’t consider yourself an expert on the subject just because you couldn’t make power with FI.

You go ahead and have your rebuttal, and then let’s just drop this and quite wasting bandwidth.

 

Bmonte; a couple of points. Before I make them, please understand that I LIKE my TBI.

Earlier in the thread, you said TBI flows 700 cfm. You're right, and you're wrong.

Some TBI throttle bodies do flow 700 cfm ... at 1.5" hg. That is misleading, however. Carbs are flowed at 3" hg. Every formula for calculating airflow reguirements is based on airflow at 3" hg, there is simply no comparison between a 1 or 2 bbl throttle body flowed at 1.5" hg and a 4bbl carb flowed at 3"hg. The bottom line is that a 600cfm holley 4bbl carb will flow significantly more air than a 670cfm holley 2bbl throttle body. You don't have to take my word for it, call Holley. They're the ones who explained the difference to me and gave me the formula for converting airflow at 1.5"hg to approximate airflow at 3"hg.

Second, you said TPI is not a better system than TBI. The bottom line there is any mpfi system which injects fuel directly into the intake port of the head is inherently more efficient than TBI, which mixes air and fuel in the intake. Stock 305 TPI systems made 220 hp, while TBI systems made 170. That's a 50hp difference, and the better heads on the TPI don't account for all of it.

GM designed TBI as a lower cost alternative to tuned port injection. Just as there were "economy" 2bbl models and "performance" 4bbl models offered in the 70s. TBI is the FI equivalent of a 2bbl carb. Cheaper to produce, allowing a lower sticker cost and cheaper to insure. That doesn't make TBI bad, it just makes it different. Accepting the limitations of TBI does not denigrate the system. There is nothing wrong with trying to find ways to make it better, but there is only so far you can go with it. My old uncle Elmo used to tell me: "Boy, you can't fit two tons of fertilizer in a one-ton truck". That always made sense to me.

Again, don't get me wrong, I love my TBI. It starts right up, in any weather. It runs great and can get 28mpg on the road when I keep my foot out of it. As much as I like it, however, it's going to have to go bye bye at some point, as it cannot support the horsepower I plan on eventually making.

An engine is an air pump. The more cubic inches and the higher the rpms, the more air you must be able to move through it. The best-case scenario with TBI (excluding the hogged-out, sleeved monster TBI, is 2.2" (a bored-out 454 TBI). In real-world, 3"hg terms, that'll flow around 610cfm ... at best. a 383 at 6000 rpm needs a lot more air than that. That engine with a TBI will fall flat on it's face at around 5200 rpm.

Even if you could move enough air through the engine, you're limited to a duration of less than .220@ .050 if you hope to get the thing to run right. Any more duration and you won't have enough vacuum for low-speed operation. The map sensor will go crazy. With that low duration, you won't make power very far beyond 5000 rpm, anyway. That's all there is to it.

Even if you could move enough air and run a cam with enough duration, you need fuel, too. Even with 90lb/hr injectors and increased fuel pressure, you hit a wall with the injectors' ability to simply open and close. A system utilizing only two injectors versus an mpfi system's 8 will require those injectors to cycle at 4 times the rate of the mpfi injectors. At some point, the injectors will either simply stay open, or cycle erratically (you pick which, very intelligent and experienced people have told me one or the other of those scenarios will occur) at around 5500 rpm.

Does this mean TBI is garbage? Absolutely not! It means TBI is limited. There's no reason you couldn't get 300-350 hp out of a TBI car, with TONS of torque. That's LT1 territory, and you'd make more torque, so you ought to be able to leave that 94 z28 in the dust. If you plan on making 400-450hp, you need to go another way.

My first car was a 69 Mustang with a 2bbl 351 Windsor. Shortly after I got it, I picked up a Holley 2bbl cheap and rebuilt it in shop class at school. All of my buddies razzed me about the 2 bbl and I became determined to "show them". Eventually, I swapped cams, put on headers and an Edelbrock 4bbl intake, but stayed with the Holley 2bbl, even spending a bunch of money sending it off and having it blueprinted. I eventually got the car to run pretty well, but never great. On a bet, we bolted on buddy's box-stock 600 Holley on the car. With no other changes, it ran more than 7/10 faster in the quarter mile. Even worse, the car got better mileage in daily driving, the primaries were smaller than the 2bbl, so it used less gas when I kept my foot out of it. The lesson I learned there was to not be so stubborn I couldn't see the forest for the trees. I blew a lot of money i couldn't afford in those days trying to prove an unimportant point, just because I wanted to show my detractors up.

After several year's research, here's where I am with TBI. I think the ultimate setup would be:

a 350. a 383 or 406 will need more air, especially at higher rpms. I believe you can get to 5500 rpm with a 350 before you nose over, while a 383 probably won't get much past 5000. You don't need to rev past 550 to run really fast. I've had a street car in the 11s on nitrous and 12.30s on horsepower and I shifted it at 5300 rpm. Matching components properly is the ky, not revving till the valves float

Edelbrock E-tec 170 heads. The mid-lift numbers on those heads are unbelievable; it's the 170cc runners and the high velocity. AFR 190s have 2.20 intake valves and lower velocity. They'll do better at higher rpms, as will Vortecs (old or new), but this engine can't run past 5500, the Etecs will be far superior in this engine's rpm range.

An lt4 hot cam with 1.6 rockers. The .224 duration is too extreme for a 305, but is on the ragged edge of tunability for a 350. It'll take a lot of tuning, but that's an awesome cam that places the powerband right in the rpm range the throttle body can support.

The GMPP vortec TBI intake. I believe a single-plane would actually work better due to the increased plenum volume, but I don't think anyone makes one for Vortec heads that will fit under the hood.

A bored out (to 2.2") 454 throttle body. You'll have to have the bores on the intake enlarged to 2.2"as well.

90 lb/hr injectors and fuel pressure as much as you can tune.

A lot of tuning talent and patience.

Given the air, fuel and duration limitations of TBI, I think these are the components best able to maximize it's potential. This would be a torquey, powerful engine that should have no problem cracking the 12s and would make a great daily driver as well. It'll outrun a lot of carbed 350s with less-well matched components and get good mileage, too. What's wrong with that?

 

4bbl carbs and throttle bodies are both flowed at 1.5 in/hg. If a 4 barrel carb flowed 700 cfm @ 3 in/hg it would flow LESS at 1.5 in/hg.

You are wrong on the injectors going static at 5,500. Mine was still pulling hard and not static @ the 6,500 rpm fuel shut-off.

I have run 230/230 @ .050 cams with a 108* lobe seperation in a 305. With RBobs EBL it was fine.

I was making 370 FWHP with 61 lb/hr injectors, running in the mid 30s fuel pressure.

TBI CAN support around 500 HP, especially if you use the "BIG" injectors. 125 lb/hr EACH at 12 psi! They fit this style pod.

Also MOST of the later TBI ecms switched to Asynch mode at high rpms in order to provide more rpm from the same size injector.

 

Hey Fast got a pn and place to get that big injector? 125 at 12 psi sounds too good to be true and I just happen to have that same pod laying around. I really like that pod too big diafram and ajustment screw on top.

 

Duh! You're absolutely right; I had it backwards. 4bbl carbs and throttle bodies are flowed at 1.5"hg and 1 and 2bbl carbs and throttle bodies are flowed at 3"hg. My original point, however, still stands. A 600 cfm Holley 4bbl carb flows SIGNIFICANTLY more air than the biggest 2bbl TBI throttle body. Holley's formula for converting 3"hg airflow to 1.5"hg airflow is: CFM @ 3”HG X 70.7% = CFM @ 1.5” HG, so a Holley 670 flows 474 cfm at 1.5"hg. And, according to Holley, the 670 cfm figure was arrived at without the injector pod on, so the "real" number would be lower still.

.

With two injectors, each would have to cycle 13,000 times per minute at 6500 rpm (twice per revolution). According to Scott at CFM Technologies, the mechanical limit of a GM injector is less than 11,000 cycles per minute. After that, it's wide open and is flowing as much fuel as possible; the engine can't make more power past that point. He also said that at above 90% duty cycle, but before it defaults to wide open, you run into erratic operation.

Wow, that is a lot of cam. One of the reasons I'd pretty much decided not to stay with TBI was because I couldn't run the cam I wanted. Everything I've seen on here and everything I've heard says tuning anything over 218 duration is nearly impossible. I moved home to to Tulsa a year ago (home of Ed Wright and Fastchip.com). I went and talked to him about what I wanted to do. As soon as I mentioned wanting to run a cam with more than 218 duration, he flatly announced it can't be done. I would love to know how it can be done. What is RBob's EBL? Can you link me to any posts describing how you tune a cam that big?

That's a lot of horsepower! If it's a manual trans, figure 10% parasitic loss; that's 407 flywheel hp. If it's an automatic with 20% parasitic loss, that's 444 flywheel hp!

Taking the lower figure:

407hp * .45 BSFC = 183.15
2 injectors * .9 Duty Cycle = 2.22
183.15 / 2.22 = 82.5 lb/hr injector

Using the higher figure:

444 * .45 BSFC = 199.8
2 injectors * .9 Duty Cycle = 2.22
199.8 / 2.22 = 90 lb/hr injector

Clearly, it's theoretically possible to flow enough fuel with a TBI to support those horsepower numbers. Using a stock fuel pressure of 13psi and a new fuel pressure of 35psi, a 61lb/hr injector would flow 100.09lb/hr. here's the calculator:

http://www.csgnetwork.com/fiflowcalc.html

I'm curious about the pressure, though. Awhile back, VA454SS said he knew a GM engineer who said they'd tested their injectors at up to 70psi and had no problems with the pintle seating. Scott at CFM, however, says that at above 30 psi, you begin to see the pressure affect the spring's ability to close the injector quickly enough and force the pintle off the seat. I don't know why that would be a problem when TPI injectors run at 45 psi stock, but he said TBI injectors are different because of their size.

Where are you getting 125lb/hr injectors, and where are you getting that pod? I thought the 90lb/hr 454 injectors were the biggest you could get for GM TBI. I'd heard they used larger injectors in Brasil, where they use ethanol as a fuel, but I thought it was just B.S. Maybe not. Will that injector pod fit our throttle bodies?

 

I found the 125 lb/hr injectors in some Mexican Silverado's around 1990-1995 with the 292 I6 TBI in them. The TBI looked like a cross between a crossfire and the one that is on the Tech4. It used the tech4 style pod. I picked the injectors up because I knew they would be big because of the fact that they used 1 for 292 cubic inches. Brazil makes a 292 TBI that runs on alcohol, I imagine they have injectors that are even bigger in that application.

They have a 5 digit part number, but the number brings up nothing at my local GM dealer. I have flowed them on an injector flowbench and they were both right at 125 lb/hr.

The pod I have like that in my garage, bolted straight to a regular GM TBI.

370 FWHP is 370 Flywheel Horsepower I already did the conversion for you. The RWD numbers through a 700r4 and greater than average driveline losses (2 piece driveshaft with carrier bearing) was 301 RWHP

The 670 was flowed at 1.5 in/hg according to holley. I know of a stock big block TBI that was flowed at 28 in/h20 and flowed over 700 cfm. Converted to 1.5 in/hg in Desktop Dyno's airflow conversion calculator, that equals 596 CFM! That was with the pod installed.

Someone on here flowed a stock SBC TBI with the pod installed and it flowed 500 CFM @ 28 in/h20. That is 426 CFM @ 1.5 in/hg. Lots of people are able to get good power from a 390 holley when the rules require it.

Take a look at this MPFI 250 I6 from the Brazilian market. They have alot of weird things down there.

 

Ed Write, that explains alot. I see fast pointed out your biggest misconseptions, I'll be back on monday to bring the rest of the TECH.

 

BTW, here is a couple of screenshots displaying the difference in my cammed 305 and my nearly stock bolt-on crate 350 at idle in gear.

Cammed 305



Notice that it is idling at 65 KPA which is 10.8 in/hg of vacuum, it dropped even lower when the A/C was on, to around 70-75 KPA.

Near Stock 350



Notice that it is at 45 KPA which is 16.7 in/hg of vacuum, with the A/C on.

 

What does that explain?

 

Generic Mail order tuning is what BM is getting at.

 

First, I'm talking about basic tuning that is done on a dynojet with a wideband 02 sensor, then driving around with a datalogger and dialing in the tune till it's perfect. That's the service he offers in person. I've been out there a number of times and watched him do it, and I have a number of friends here who've had it done and are totally satisfied with the service, including one of the most badass rock crawlers I've ever seen, which runs TBI because it's so smooth and reliable, even at weird angles..

I share the disdain virtually everyone who is in the know on here has for "off the shelf" chips as sold by Hypertech, Jet Chip, and even by Ed Wright through Fastchip. There are just too many variables involved to have one generic, "fits-all" chip.

Despite what most experienced tuners on here think, however, you CAN get good chip tuning through the mail. I met a guy from this board who had a third gen Camaro with a 383 TPI, automatic and 323 gears. He eventually got the car to run a best of 12.03 in street trim, and all of his chip tuning was done through the mail. Mike would datalog while driving around and while on the dyno, then email the datalogs to the tuner. It took 7 chips to get it dialed-in, but the car drove great around town, got 25+mpg on the highway and ran like a banshee at the track. I talked to the guy who did the chips for that car a year or so ago. He gave me a number of references. When i followed up on them, all I got were raves for him and his work.

 

You are correct in saying that getting fuel out of the manifold is beneficial. It doesn’t make the engine more “efficient” everywhere. It does help with fuel atomization, but mostly at low rpm. Even with MPI injection the fuel gets sprayed on a closed intake valve, and then has to get atomized when the valve opens and the air gets moving again. I’ve tuned a TBI setup, so I know what has to be done to work around a wet flow system. At WOT there is nothing inherently wrong with a wet flow system. It’s only transitional events that require special attention. MPI will NOT make more power because of where it injects fuel, it may have a slightly better BSFC but that’s it.

What happens in the combustion chamber is all that matters. If you can get the proper amount of fuel and air into an engine, then you’re going to make power. The motor doesn’t care how many injectors there are or even where the injectors are. It most certainly doesn’t care how many barrels the throttle valve has as long as it doesn’t cause a restriction.

Your just dead wrong on why the TBI motors made less HP. Have you ever even looked at the cam specs for a TBI motor? The duration is in the 180/190 range at .050 lift. Lift is only .380ish. That’s freakin TINY. The SP heads do restrict the motor a bit on the top end, but dyno test by members here have shown they trade 5-10 HP for a solid 10 ft/lb’s below 4100 rpm. The other 30 HP is in the cam, no questions asked. I would bet money that a BB tbi unit on a performer intake would make the same power, if not more top end power than a TPI setup. Heck on a stock TPI motor, the 350 TB would make the same power.

As for airflow, there are some conflicting numbers floating around. I don’t pay much attention to those, basically because flow benches don’t simulate what actually goes on inside an engine. I do know for a fact that a BB TB will NOT restrict a 400+ hp motor. I know this because the guys that are making the power say they are not pulling any more than 1” of vacuum at WOT at 6 grand plus. Holley themselves say that as long as your not pulling more than 1.5” of vacuum you don’t need a bigger carb. A BB TB is 1mm smaller than a TPI throttle body. That’s a full 2 inches, your 2-barrel you built back in the day didn’t have anywhere near that size bores, plus it had a booster right in the venturi.

It’s very simple, TBI is NOT air flow limited. We are limited by the size of injectors we can get. Fast seems to have found the cure for that with the alky injectors. This “wall” you speak of it simply the injectors going static. It has nothing to do with TBI, you can do the same thing with MPI. When injectors go static, you’re simply asking them to stay open longer than they have time to. How long you can hold the injectors open is completely dependent on the RPM, it’s not some arbitrary number. This is why we need big injectors to get enough fuel into the motor in the allotted time. This is NOT a TBI specific problem, don’t tell people it is. When you tune, you can control how long the injector is held open. TBI does fire the injectors twice as often as MPI, this is mostly negated by the fact that TBI has Peak and Hold injectors, which get the injector open faster. Like Fast mentioned, there is an asynch mode that bases pulse width on time only, and is completely independent of rpm.

Ohh and Ed Write sucks because he charges big bucks to do what is provided for free here. Also the reason Ed won’t tune anything with a cam bigger than 220* is because he wont’ be able to get it drivable in 7 chips. He is not getting a motor optimized in 7 chips, I don’t care how good he thinks he is. He may get the max HP on a dyno and get the thing to pull itself around town, but he is not getting things as good as they can be. You can tune big ole hary monsters, but most of the time you won’t do that with TBI because big ole hary monsters better make more than 450 HP.

In conclusion, for anything less than 400 HP TBI will make just as much HP as TPI, maybe more with the right intake under the TB. It will also do this for less money.


Edited: Got Mr. tunedport confused with Sean, sorry bout that.

 

Ok, let's settle this once and for all. When I first began researching TBI 3 years ago, I saw that no one seemed to know for sure what the various throttle bodies flowed. I called Holley to find out, and was told 4 bbl carbs and throttle bodies were flowed at 1.5"hg and 1 and 2 bbl carbs and throttle bodies were flowed at 3"hg. When I asked the guy how you could calculate airflow needs for a specific engine size for TBI when the formula requires airflow @ 1.5"hg, he gave me a conversion formula they use: airflow @ 3"hg * 70.7 = airflow @ 1.5"hg. This formula, by the way, when applied to a Holley 670, looks like this: 670 * 70.7 = 473.69, or 474 cfm @ 1.5"hg.

I posted this information on here and had people jump all over me. I followed through with an email to Holley, and was again told 3"hg.

As I went about learning more about TBI, I made a lot of calls and wrote a lot of emails to people who earn their livings making power with TBI; CFM Technologies, Jet Performance, etc. In each of those calls and emails, I asked the 3"/1.5" question. In each case, I was told 2 bbl TBI throttle bodies are flowed at 3"hg. Not once was I ever told 1.5".

About a year ago, the issue sprang up again, and the debate got pretty hot and heavy, with one guy insisting he'd spoken to Holley and been told 1.5"hg. Since I was about to buy a bored out 454 throttle body, I wanted to make absolutely sure I was right, so I again called Holley, speaking to the engineer in charge of their TBI fuel injection. He emphatically stated that ALL 4bbl carbs and throttle bodies are flowed at 1.5"hg and ALL 1 and 2bbl throttle bodies are flowed at 3"hg. He went on to say that it wasn't simply a Holley policy to do that, but it was an industry standard. He explained the reasons behind it, but it was all way over my head.

Now, here we are again. Last night, I again emailed Holley about this. This morning, I got the following reply from warrenwh@holley.com:

++++++++++++++++++++++++++++++++++++++++++++++

3 inches
Yes

WW

Your question was:
Regarding your 2bbl, 670 cfm throttle bodies; can you tell me if these throttle bodies have been flowed at 3"hg or 1.5"hg to arrive at 670 cfm?

My understanding is that you flow 4bbl carbs and throttle bodies at 1.5"hg and 1 and 2bbl carbs and throttle bodies at 3"hg. Is that correct?

Thank you.

If you have further questions, please reply directly to this email with history without altering the subject line.

++++++++++++++++++++++++++++++++++++++++++++++

If anyone wants me to forward them the original email, I will do so gladly. Email me at seanof30306@yahoo.com.

Now, this is the 4th time that Holley, the manufacturer of the throttle body in question, has told me that they are flowed at 3"hg. I've also had over half a dozen industry experts state the same thing, and not once has anyone in the industry told me 1.5"hg. The issue is settled.

Fast, please understand that I'm not attacking you here, but I think it's important that as much of the incorrect and erroneous information about TBI be corrected as possible. There is so little information on TBI available, and I hate to see people get discouraged and quit messing with theirs just because there is so much misinformation and confusion about it.

 

Sorry for the mis-information then. That was the word of one of their techs when I talked to them a while back. Actually, it was when I was considering purchasing one for my 3.4 TBI. FWIW, I ended up with a 4.3 TBI and modified the linkage to bolt up. The other throttle bodies flow as stated though.

I know of a stock big block TBI that was flowed at 28 in/h20 and flowed over 700 cfm. Converted to 1.5 in/hg in Desktop Dyno's airflow conversion calculator, that equals 596 CFM! That was with the pod installed.

A stock SBC TBI with the pod installed and it flowed 500 CFM @ 28 in/h20. That is 426 CFM @ 1.5 in/hg.

Looks like the 454 TBI flows better in stock form than the holley does

Don't overlook the fact that throttle follower logic will fully open the IAC valve as well. The IAC valve can flow a substantial amount of additional air when it is fully open..

 

Hey, Fast, on that note, have you looked much into the throttle follower stuff to do that? I haven't looked into it at all, is it set stock to open fully at open throttle, I wouldn't think that it is.

As far as the 454 flowing mroe than the Holley, I would really find that hard to believe, I bet Holley was just conservative with their flow numbers. I have one and it is pretty large and I'm sure flows a ton, I've also got the bores radiused and shafts shaved.

 

Stock the IAC opens about 145 counts max. With the EBL, I have it opening all the way.

The 454 TBI is radiused from GM, but still has thick shafts.

The big block TBI flow numbers are courtesy of Airdeano on Fullsizechevy.com.

Where is the missing 122 CFM from the Holley vs. BBC?

 

I disagree with you. First, the main advantage of MPFI over wet flow is efficiency. Very precise amounts of fuel are injected directly into the chamber at very precise times, so less fuel is used overall to achieve the same power. Also, if your injectors are working properly, each cylinder recieves the same amount of fuel, with the same level of atomization, as every other cylinder, so you don't get individual cylinders which run rich or lean as you do in wet flow systems (although some say the cylinders furthest from the throttle body tend to run richer in TPI cars; I haven't seen it.).

There is a difference in power, as well. Even though you tend to shrug it off, injecting the fuel directly into the cylinder eliminates all of the puddling, pooling and reliquidification inherent in a wet flow system. I frankly don't understand your point about spraying fuel on a closed valve. The whole point of MPFI is to spray fuel into the cylinder only on the intake stroke, rather than continuously, as in a wet flow system. While some small amount of fuel may hit the valve as it opens and closes, it is a miniscule amount when compared to the puddle of fuel which builds up on the closed valve in a wet flow setup.

And that "slightly better BSFC? That is huge! An average street engine has a BSFC of around .5, while a finely tuned race engine will have a BSFC of around .45. That's not much of a difference. Even a slight improvement in BSFC makes a big difference in power.

You're comparing apples to oranges. You want to take the best TBI setup available and compare it to a stock TPI. Take that TPI, but a Big Mouth base, AS&M runners, a bigger throttle body and injectors on it and see what it does. I believe if you swapped a stock TBI onto a TPI engine, or if you swapped a stock TPI onto a TBI engine, and properly tuned each setup, the TPI would make more power. I'm not saying TBI sucks, I'm saying TBI wasn't designed to make power, it was designed to be cheaper to manufacture and sell than TPI. It is what it is. Neither good nor bad.

Sorry, but there ARE airflow restrictions:

Engine Size (CID) * Maximum RPM / 3456 * % Volumetric Efficiency = CFM needed

Since we're talking about a 383 here:

383 * 6000 / 3456 *.85
565.19 cfm

Bottom line? A 383 at only 6000 rpm need 565 cfm. A Holley 670 flows 474 cfm. I've used this formula for years to calculate carb size. While it is a little conservative, you ususlly need more air thatn it indicates, it clearly shows the airflow limitations of a TBI. Let's see what it needs at 5500:

383 * 5500 / 3456 * .85
518.092 cfm

How about 5000?

383 * 5000 / 3456 * .85
459.94 cfm

Ok, the 670 flows enough air at 5000, but, at 5100:

383 * 5100 / 3456 * .85
480.41 cfm

There's the limit. A 383 with a Holley 670 should nose over between 5000 and 5100 rpm. Here's a calculator for it:

http://www.csgnetwork.com/cfmcalc.html

By the way, a 350 wouldn't nose over till 5500. The more cubic inches, the more air you need at any given rpm. That's why I recommended a 350 over a 383. 383s cost more to build and you just can't flow enough air with one to take advantage of the extra cubic inches.

All this means, by the way, is that you need to build a TBI to make best power below 5500 rpm. Not bad, just different.

Airflow concerns displacement and rpm, it has nothing to do with restricting horsepower. Horsepower is determined by fuel flow. Airflow affects this only by limiting what rpms an engine can continue to make power at. If your 383 can make max horsepower below 5000 rpm, the only thing stopping it from making any specific HP number is fuel (and efficiency).

Once again, you're comparing apples to oranges. In a dry-flow MPFI, all the throttle body flows is air. In a wet flow TBI, the throttle body flows both air and fuel. The fuel displaces a significant amount of air, so a 50mm TPI throttle body flows significantly more air than does a TBI throttle body of the same size. Additionally, A TPI has a huge plenum; a TBI does not.

And I wasn't comparing my 2bbl carb to TBI. I was making the point that I spent a lot of time, energy and money trying to make that 2bbl do something it wasn't designed to do, when all along there was something designed to do what i wanted all along; a 4bbl.

First, TBI fires the injector four times as often as TPI, not twice. Each injector in an MPFI fires once every other rotation, on the intake stroke for that cylinder. In TBI, each injector fires twice per revolution.

The injector limit is not the amount of fuel the injector can flow, it is the mechanical limit of the injector to cycle. At approximately 98% duty cycle, an injector goes into asynchronous mode, where it is recieving firing pulses so quickly that it remains open all the time, never having a chance to close. At that point, it is merely a jet, flowing as much fuel as it can. It's not that simple, though.

A fuel injector is not designed to operate at over 90% duty cycle; for a number of reasons. First, at a point somewhere between 90% duty cycle and when it goes into asynch mode, the injector begins operating erratically. It will be in the process of closing, get a firing pulse and attempt to reopen, either reopening completely, reopening partially, as it must now overcome both spring pressure and the inertia of it's closing movement, or miss the pulse entirely and continue to close. This causes erratic fuel flow, lean and rich cylinders, etc.

Operating in asynch mode for extended periods of time also overstresses the injectors' springs and can cause failure or weakening of the springs.

Raising fuel pressure to flow more fuel only adds to the problem. Higher fuel pressure places more resistence against the spring as it attempts to close the injector, making the process take longer. At 90+% duty cycle the higher fuel pressure can cause even more erratic operation before the injector goes into asynch mode.

Going to bigger injectors can be problematic as well. The mechanical limit of bigger injectors is lower than that of smaller ones. At what point that mechanical limit offsets increased fuel flow, I don't know.

And, when you increase the amount of time an injector stays open, you lower it's mechanical limit. if it's open longer, it takes longer for it to complete the opening/closing cycle. You'll reach 90% duty cycle at a lower rpm. Again, where the benefit of having the injector stay open longer is offset by the decreased duty cycle, I don't know.

The bottom line is that there is a "sweet spot" for any potential combination, where the injector is flowing as much fuel as possible at 90% duty cycle that is the limiting factor in fuel flow. I don't have all the data, but I'm figuring the GM engineers did. I don't think it's an accident that TBI runs out of air at between 5000 and 5500 rpm when the mechanical limit of the injectors is somewhere in the neighborhood of 11,000 cycles per minute (5500 rpm).

Now, factory can always be improved upon, but there are limits to what you can do. Given the amounts of air and fuel we can flow, I still say the best we can do is 350-375 hp at under 6000 rpm. And that's not a bad thing. If you want an LS1 killer, though, you're going to have to go another way.

First, it's not free. You have to buy equipment to burn your own chips. I also place a value on my time. Now, if someone likes to tune, great. if you have a setup that you plan on making a lot of changes to over time, you'd better learn to like to tune, as the tune will change with every parts change you make, and you'll go broke trying to keep it tuned right. If, however, you don't have any interest in learning to tune, and you plan on setting your combination from the start, there's nothing wrong with using a tuner. I just don't understand the naked hostility shown by you and others towards it. It's your way or the highway, and you feel a need to insult and denigrate any other way suggested. I don't buy it. You can tune all your life, but you'll never get WOT as well as you will in two or three runs on a dynojet with a wideband.

As far as daily driving, it takes more time, but what is the difference between your driving around and datalogging, then going in and making changes, my driving around and datalogging, then going back to Ed Wright and letting him make the changes, or Mike Crews' (Mr. TPI to you) driving around and doing the datalogging and emailing the datalogs back to his tuner, who makes the changes? It clearly worked for Mike. How can you find fault with a 383 that makes 400 rwhp, runs low, low 12s in street trim, drives great around town and gets 25+ mpg on the highway? I'd say that was a pretty good chip tune, wouldn't you? Just because he didn't do it your way doesn't mean he did it wrong.

I watched Ed Wright tune a TBI pickup for a guy I know. It took two runs on the dynojet to get the WOT right. Then Ed ran the truck through several dyno runs he said were designed to simulate daily driving conditions. Ed took the datalogs from those runs and burned another chip (#2). Then he took the truck for about a 30 minute drive around a course he said he uses on every tune, with both in town and highway driving. He burned another chip (#3). He then took another short drive, pronounced the truck "roughed in" and my buddy drove off. Over the next week, he drove the truck daily, gave his impressions to Ed over the phone, and did some datalogging as per Ed's instructions. He went back, Ed took the datalogs and burned chip #4 and it's done. My friend loves the way the truck runs and says he's getting better gas mileage than he did stock, with a lot more power.

And, as far as tuning cams with over .220 duration? Look back on this board at all of the discussions on cam selection and see what the experienced TBI tuners are saying. It's almost unanimous; cams with over .220 duration are incredibly difficult to tune. That's not Ed Wright talking, that's the consensus of this board.

Umm, I could swear that my point, which you disagreed with, was that TBI couldn't make over 400 hp. Also, I believe, if we took the same long block, put a stock TBI on it and a stock TPI on it and tuned both properly, the TPI would make more power. Now, the best base, runners and throttle body available for the TPI are definitely more expensive than the best intake and throttle body available for a TBI, and you only have to buy two injectors for the TBI while you have to buy 8 for the TPI, but, by your own admission, you'll max the TBI out at less than 400 hp, and you can make more than 400 hp with the TPI. The TPI will also make sick torque; much more than the TBI. So, once again, it's apples and oranges. If you want a nice, peppy, efficient street car that makes under 400 hp, there's no need to rip out your TBI and switch to TPI, you can achieve it with what you have. If you must have more, it's time for a carb, TPI, Stealth Ram, Accel DFI, F.A.S.T., etc.

TBI is different than MPFI; it's not as efficient, but it's also less expensive. HP per dollar invested? Clearly you can do better with TBI (up to a point) if that's what you already have. If HP per dollar invested is the only consideration, however, nothing compares to a carb.

 

Unless that's .28"hg, not 28"hg.

If it is .28"hg, the 454 throttle body flows somewhere in the neighborhood of 490 cfm @ 1.5" and the SBC throttle body is somewhere in the neighborhood of 355 cfm, using the 3"hg to 1.5"hg formula. Not completely accurate, but I'm guessing not too far off, either.

In going over my notes, I've come across a couple of things. The guy who sells bored out throttle bodies on ebay told me once he'd compared a Holley 670 to a stock 454 throttle body on a flowbench and the Holley flowed more, but his bored out 2.2" 454 TBs outflowed the Holley. I believe him, I've bought one of his throttle bodies and was very happy with it, as was gunnyhighway and several others from here who've done business with him.

His methodology, however, leaves something to be desired. For examle, he says his bored out 454 throttle bodies flow 750 cfm. When you ask him about it, though, you find out he calibrated the flowbench by putting a 650 Holley 4bbl on it, adjusted the bench till that carb showed 650 cfm, then tested the throttle bodies. This makes me a little dubious about the numbers, but I do believe he's being straight about the results he got and what outflows what.

I also believe it was the guy from Jet Performance who told me they'd flowed a stock SBC throttle body at 390cfm with the injector pod on.

 

I want to know who told you Asynch will hurt the springs. Some STOCK calibrations run entirely in Asynch mode. My 1987 2.8 TBI did anyway, it had over 200,000 miles on the originol injectors, WOT shift points were 5,500 rpm as well.

A little TBI airflow info for you.

https://www.thirdgen.org/techbb2/sho...ow+measurement

BSFC is in no way related to the HP output of an engine. It is simply the amount of fuel that it takes to make a given HP number. The reason "HOT" engines have lower BSFCs in the upper RPM range is due to the nature of friction. Less restriction, less reciprocating mass, less windage, less parasitic drag, all increase power without substantially increasing the fuel demand. That gives a better BSFC.

Then you talk of MPFI not puddling fuel. Guess what, TPI is BATCH fire not sequential. It is not a precisely timed event. If you really think TBI is that bad, put EGT sensors iin each header tube. I have! With a stock GM intake or Edelbrock 3704 the temps were within 20* of each other at all times.

I have swapped a stock TBI setup on-top of a stock Q-Jet carbed 305. I picked up HP and low-midrange torque over the perfectly tuned Q-Jet. TBI would make basically the same HP as TPI on a TPI longblock.

A 454 TBI was not a restriction to the least degree at 6,500 RPM on a 312 making 370 RWHP. The MAP was reading 98 KPA, through the air cleaner and stock Van intake tract, including the 90* intake duct immediately above the condensor.

BTW, I have access to a Mustang Dyno, it is alot better for tuning than a Dynojet is. I can run in a variety of constant, part throttle runs, simulate WOT acceleration runs (drag racing), measure HP & TQ, etc. When I am tuning I usually run a wideband in the stock 02 sensor location and use the narrowband output on the wideband controller for the ECM. Prior to the EBL, I ran my TPS, MAP, and RPM signals into my wideband, and inputed it into my Laptop. Helps narrow down on a tune 10x faster than the old 160 baud.

Its funny how there are guys with 454 TBIs making more than 400 HP @ 5,500 rpm, using TBIs!!!! No nitrous and no superchargers!

I would love to see a stock LTR TPI make 400 FWHP. I made around 340 FWHP with a STOCK TBI and STOCK TBI intake.

Why is it that I doubt the 400RWHP TPI 383 was a Speed Density setup! If not the 8192 baud rate helps alot in the tuning world. TBI will soon have the EBL which will kick the 8192s baud rate out the door.

There is a big difference between one of us tuning a car and sending datalogs out to have changed. For one, datalogs are only 1/2 the story. Plug cuts, engine sound, vehicle performance, 1/4 and 1/8 mile runs, as well as dyno time and wideband readings are all used. I have serious doubts that Ed Wright would spend the same effort to dial in my Tune than I did. It really doesn't take all that long either. You can get it close in about 20 chips, perfect in about 200. With the EBLs faster baud rate, you can get it close in about 2 chips and near perfect in 20!

230/230 in a 305 really was not that difficult to tune, even with the old 7747 ECM!!

 

It was 28 in/hg not .28. I have flowed several TBI throttle bodies and the midget stock 2.8 unit flowed more than 355 cfm when converted to 1.5 in/hg.

 

I forgot to mention that my tune has to pass DFWs tough dyno smog tests.

BSFC

 

Holy &$(*&(@ I don't even know where to start with that response.

Fast covered your biggest misunderstandings, I'll be out of town for the next few days, so don't think I'm walking away from this argument.

 

That's according to Scott at CFM Technologies. Additionally, the tech I spoke to at Holley last year said the formula posted on their website for calculating injector size indicated 90% duty cycle because the injectors in their EFI systems weren't designed to operate at over 90% duty cycle for extended periods of time.


I'm confused. Nowhere in that very technical thread do I see airflow at 1.5"hg. All I see is airflow at 28", then a conversion to 2"hg. Again, apples and oranges when the formula for calculating airflow requirements has a prerequisite of airflow at 1.5"hg. Did I miss something?



Honestly, I don't know enough about this to have a further opinion. Everything I know about BSFC comes from one conversation with a Holley tech almost two years ago. I could easily be wrong.



You're right, TPI is batch fire. I hadn't considered that. Still I believe there will be less puddling and pooling with the injector directly in the port than on top of the intake.


When you say perfectly-tuned Q-jet, are you saying it was tuned using the same dyno-tuning methods you use on the TBI, and swapping metering rods, etc? Also, there's a HUGE difference in the computer-controlled Q-Jet that came on third gens and non-computer models. remember all the grief Tim Moore had with his in that project Camaro he did for CHP? They never could figure out why it wouldn't make any power.



312 * 6500 / 3456 * .85
498.78 cfm

Clearly within the real of possibility. Smaller displacement engines need less airflow. A 312 needs less air at 6500 rpm than a 383 does at 5200 rpm. Being able to figure out which combinations it will work with and which it won't still hinges on how much air that 454 TB actually flows at 1.5"hg.



Who? I never seen anyone on here posting those kind of numbers.



Not accusing you of lying, but I find that hard to believe. What was the rwhp number? Were you running stock heads? You're talking about nearly doubling the horsepower of the engine with the stock intake and throttle body. Actually, you ARE talking about doubling it, the stock figure was 170 fwhp.


https://www.thirdgen.org/techbb2/sho...threadid=84340

There's the thread. It's a long one, but, if you take the time to go through it and see the progressions he made, it's a blueprint for someone who isn't a master engineer to be able to get amazing results just by being thorough and patient in their research. I personally saw the car run 12.10 at Atlanta dragway in street trim. He drove up for a Year One event (over 150 miles), cooled the car off, stuck it in "D" and pulled up to the line.



Then, I guess Mike should be unhappy with his great running car, and my pal with the pickup should send Ed Wright hate mail, even though he's perfectly happy with it? The process you described using on the Mustang dyno doesn't sound much different than what I described Ed's doing on my buddy's truck; why is it bad and yours good?

You clearly know A LOT about this subject. Couldn't we assume, then, that your knowledge and experience would allow you to reach a near-optimal tuning solution much more quickly than someone with less knowledge and experience? And, if that is true, isn't it possible that someone who makes a living tuning efi applications and has done a lot of TBI cars and trucks might be able to reach a near-optimal tune even faster? Sure, there may be an even better tune hiding in the ecm of my pal's truck, but he's totally happy with the power, driveability and mileage he's getting now. Why is that a bad thing?

Also, what is the EBL?



I'm not arguing that point, I'm merely passing along the information I've been given in this forum over and over since getting my TBI car. Time and again, knowledgable people like RBob and Dewey316 told me it would be nearly impossible to get the LT4 hotcam I have to run in my 305. Nothing would make me happier than to stick it in and drive my car down to have you tune it for me; I'm only 4 hours away. Just tell me when, how much, and what I need to get done beforehand.

 

Regarding BSFC, I responded to BMonte's shrugging off a slight improvement in BSFC by saying: " And that "slightly better BSFC? That is huge! An average street engine has a BSFC of around .5, while a finely tuned race engine will have a BSFC of around .45. That's not much of a difference. Even a slight improvement in BSFC makes a big difference in power."

I was willing to concede the point to you, as I was only parroting what I was told by a Holley tech, but, after reading the link you sent, it's clear I was right!

Here's what you said: "BSFC is in no way related to the HP output of an engine. It is simply the amount of fuel that it takes to make a given HP number. The reason "HOT" engines have lower BSFCs in the upper RPM range is due to the nature of friction. Less restriction, less reciprocating mass, less windage, less parasitic drag, all increase power without substantially increasing the fuel demand. That gives a better BSFC."


What Holley told me, and what your Wikepedia link conformed, is that BSFC is a measure of an engine's efficiency. Improving BSFC means you're making the engine more efficient; you will make more power with the same amount of fuel. So, BSFC is absolutely related to the horsepower output of an engine, as it relates to a fixed amount of fuel, which is exactly what I was saying.

Wikepedia says an average car has a BSFC of .53, with the best possible number being .44. That looks pretty close to what the Holley engineer told me, and what I posted..

Here's their example:

400 HP * .45 BSFC = 180

2 Injectors * .9 Duty Cycle = 2.222

180 / 2.222 = 81.081


To make that same hp with a less efficient engine with a BSFC of .5, you'd need 90 lb/hr injectors. That's a pretty big difference.

400hp * .5 BSFC = 200

2 Injectors * .9 Duty Cycle = 2.222

200 / 2.222 = 90.009


If you take those 81.081 lb/hr injectors on an engine with a BSFC of .5, however, you only make 360 hp. Same amount of fuel, 40hp difference. I'd say efficiency (BSFC) make a pretty big difference. I was right.


360hp * .5 = 180

2 Injectors * .9 Duty Cycle = 2.222

180 / 2.222 = 81.081

 

This is making me want to just pull off my Holley and go get it flowed when I get home from school. hmm maybe I'll look into that.

Fast, that's pretty cool that the EBL has it set to open, I could see that letting in quite a lot more air through the IAC!

I don't see where any of this wearing of springs in the injectors is warranted in the least. In all my time of dealing with TBI cars and helping people out around here and talking to everyone, I don't think i have EVER seen a case in which an injector failed, they just DO NOT fail, ever. As far as my experience goes, they are seemingly indestructible, things break around them but they do not fail. I couldn't see how running Asynch would have any detrimental effects on them either.


Also, sean you mentioned the xtremefi guy flowing his TBI that is bored slightly larger than 2" I believe, and he said it flowed 700cfm and calibrated it with a 650 4bbl carb, wouldn't that support the claim that TBI's are flowed at 1.5"?? If that 650 is 650 at 1.5" and a slightly larger bore 454 TBI flowed 700cfm, I'd think them to be comparable to 4bbl carbs flow ratings.

Personally, I like doing some mathematical solutions to figure out a range for some of this stuff, but don't let formulas run your life per se. If someone is, in reality, making X amount of horsepower without pulling vacuum through the TBI and your formula says it isn't possible, that basically shoots to hell the credibility of that formula in my eyes. If an engine is making the power, its making the power, period.

Oh, and EBL is RBob's new Embedded Lockers Board setup, check out the DIY-Prom board, it will be a huge post right near the top.

As for posted numbers, look up Ben73, I believe he's running a low 12's 383 with big block injectors, not running static and I'm pretty sure he revs it decently high. He's making big horsepower and is an experienced tuner as well and would know if he was restricted and that isn't the case. It can support more than you think, believe me. my $.02

 

Please don't take this the wrong way, I am not attacking you personally, just some misconceptions that you have. Apparently I have some as well.

Asynch does not mean that the injectors is running at over 85% duty cycle. It simply means that it is firing at a (I believe fixed 80 HZ).

The highly technical thread gives the dry flow in 28 in/h20 (the same constant that heads are flowed at) as 574 cfm on a stock 4.3/5.0/5.7 TBI with the injectors installed. I actually was actually thinking it was around 490-500 @ 28 in/h20. Run that through DD2000 airflow calculator and it is about 490 CFM @ 1.5 in/hg (probably the number I was thinking of).

I can see one place where a race prepared engine could make more power on a given injector size. 90 lb/hr injectors will make more HP @ .450 BSFC than at say .560 BSFC.

As far as puddling and pooling, that is much more of a problem at idle and low-engine speeds, not at 3,000+ as turbulence and velocity will help keep the fuel in suspension. The reason for MPFI and then SFI was totally emissions.

The Q-Jet was from my 1983 G20 van and was non-electronic. The only electric plugs on it were for the A/C idle kicker and the choke. It was heavily tweaked to hold a wideband a/f ratio of 12.6-13.00 throughout the whole RPM band. The timing curve was very aggressive as well for pump gas (weird ESC equiped engine)


I know that a 312 @ 6,500 will draw less air than a 383. It was still making around 370 FWHP (typo earlier and hit R instead of F and said 370 RWHP and then could not edit).

Take a look at 454SS.com. VA454SS is making a good amount of HP based on his track times. Search for him.

340 FWHP was on my old 355 as detailed here. It eventually went 279 RWHP.

355

I am not really faulting Ed Wright, just saying that it is hard to get it fine tweaked in the little time that he will spend with it. Time is Money. You can either buy the burner, dataloging equipement and do it yourself from then on for nearly free or you can get it done once by a tuner and get charged the same amount. To me it is unreasonable to toss out $200-300+ for someone to tune my ECM for one time, when less money will get me near infiinite burns.

Your friend might be amazed at the power, driveability, and MPG he is getting now, but what if there is more left in it? I was able to get 17.4 MPG, towing a 26 ft pontoon boat with 5 people and alot of fishing gear in the boat, through city traffic and onto the highway. A dozen stoplights, 10 miles of stop and go, then 40 of open road doing up to 60-65 mph. It was about 80-85 outside as well, so the A/C was on the whole trip.

EBL

This is the WhatsUP display for the EBL just before arriving to the lake on Saturday, boat in tow. Notice the clock is slightly confused. The run time was 1:38 in that screenshot.





As far as what I see as the perfect TBI engine (for a car), I would go with the Car Craft Humble Pie 350 build that they did a year or so ago. Basically a Hot Cam in a 330 HP 350 Crate engine and it was able to make about 400 FWHP/428 ft/lbs and still pull 15.5 in/hg of vacuum at idle (about 3 in/hg more than my 305 was making). Go with an edelbrock carb vortec intake, TBI adapter, 454 TBI, go with some 70ish lb/hr injectors at around 32 psi, then run the EBL to control it. GP Sorenson 68 lb/hr injectors have no issues running around 35 PSI fuel pressure for about 111 lbs/hr each. Even if that build was using .500 lbs/hr/hp you would still have plenty of fuel at 85% duty cycle and should be able to obtain a decent idle, IF not the EBL supports a VAFPR.

.Humble Pie

116x2/.500x.85=394HP which is close enough as the BSFC will surely be lower at peak HP. Not to mention you can push the injector up to about 90% DC

 

What I was trying to say by it, was that it is a measurement and not relating to the actual potential of the engine itself. True that it greatly effects injectors sizing, but as far as HP, with the right amount of fuel, the engine will make the same. This is one of the reasons that I like the fast burn style heads, such as the Vortec or Swirl Port and don't recomeend using old style heads on TBI engines. Take note of how much extra fuel Dewey used at all RPM points with his 416 swap vs. his 187s.

 

Dude, by the time the manufacturer of the Holley 670 tells me for the 4th time over the course of two years that not only are their 2bbl throttle bodies flowed at 3"hg, but all 2bbl throttle bodies are flowed at 3"hg; by the time the two companies marketing bored out TBI throttle bodies, CFM and Jet, tell me all 2bbl throttle bodies are flowed at 3"hg; by the time the chief of engineering at Barry Grant tells me 2bbl throttle bodies are flowed at 3"hg; by the time Kevin McClelland, the tech editor at CHP tells me 2bbl throttle bodies are flowed at 3"hg, I'm going to believe them. I'm convinced. 2bbl throttle bodies are flowed at 3"hg.

Another thing I'm going to do is realize that logic and reason just cannot reach some people. I posted my documentation; a copy of the email is right there. I posted the Holley engineer's email address. Anyone can email him, or any other engineer at Holley and get the answer. I even offered to forward copies of the email in case anyone thought I was bluffing. I simply cannot believe that after all that, someone still wants to debate the issue. I won't anymore. If you want to keep your head in the sand, go ahead.

I do have one question, though. This stupid debate has been going on since before I joined this board three years ago. In the more than 2 1/2 years that I've been involved in the debate, am I the only person motivated or open-minded enough to go to an authority on the matter or two to cut through the BS and get to the truth? It took less than 5 minutes to write an email to Holley, and less than 12 hours to get an answer. I've called Holley twice. Never sat on hold for more than 5 minutes; got an answer right away. Called CFM Technologies; no wait, instant answers. I emaile Jet performance. Answer within 48 hours. Went by the Barry Grant booth at a Year One event; instant answer. Emailed kevin McClelland, took three weeks, but got an answer. How is it that I can get answers so easily, yet the debate still rages, kept going by people who have no direct knowledge, and are too lazy or, more likely, too stubborn and unwilling to admit they may be wrong to do something as simple as ask someone who knows? It's ridiculous.

It's not the only thing, either:

"1 3/4" primaries will kill torque on an L03; gotta use small-tube headers" BRACKKKK!!!! Not so. Did it. Picked up hp AND torque through the entire rpm range.

"Ultimate TBI mods improve power" BRACKKKKK!!!! Not so. Did 'em. 0 increase in hp. 0 decrease in e.t. Sounds cool, though

"3.42 gear is too small, gotta do a 3.73" BRACKKKK!!!!! Not so. Did 'em. Picked up 1/2 second over 3.08s. Wheelspin problems and 2.2 60' times make it clear 3.73s would be too much gear.

"G-Tech is a great tuning tool; don't need to go to the track or dyno if you have one". BRACKKK!!!!! have one, was set up by a factory rep, set it up with exact car weight, ran it at the track and compared the results; no correlation whatsoever, not only in specifics, but in direction. Faster et on clocks and slower on G-tech and vice-versa. The dyno mode is just as innaccurate. It's essentially worthless beyond 60'.

I could go on and on. The thing that has frustrated me most is that I've tested all of these before stating the facts, putting the car on the dyno and the track before and after each mod, and making only one change at a time. I've backed my suppositions with fact, data and proper testing procedure, only to be jumped all over by people who often don't own the equipment or parts or haven't done the mod, who haven't dyno'd or trach tested the results if they have, or ar just simply not going to admit they are wrong.

I don't mind debate, as long as it leads to something positive. This is a freakin' joke.

 

I think I am using the wrong term; "asynch" when i should be using "static". What I'm talking about is when an injector is recieving firing pulses faster than it ability to open and close. My understand is that it eventually defaults into a wide-open position when that occurs. "Duty Cycle" is the term which describes the injector's opening and closing, does it not?



Agreed. That makes sense.



I agree, but, from reading the threads about your 355 and the EBL, it's also clear that you are extremely knowledgable about the subject, are quite skilled at tuning, and have access to some pretty serious equipment. For someone with less knowledge, skills and equipment, it can be a different process altogether, with different rewards and levels of satisfaction.


You're right, there may be more left in his tune. Now, if he had your knowledge and skills, it wouldn't be that much of a challenge to get that extra performance and efficiency, but he doesn't (I don't, either). Let's assume his car is tuned to 90% of it's full potential. What he has to decide is if it's worth it to him to buy the necessary equipment and learn something he knows little or nothing about and has no real interest in learning. Yes, it would be nice to have that extra 10%, but the real question is whether the expense and effort of getting it is worthwhile to him. For some people, the answer is an easy "yes". For others, it's an easy "no". There is no right or wrong answer, everyone's will be different.


I think that's a pretty good engine. I'd spend the couple of hundred extra dollars to get Etec 170 heads over the vortecs, I think the improved flow (especially the mid-flow), and I already have an LT4 hotcam. I wonder if it might be better to install it advanced a degree or two to move peak power down a bit in the rpm range.

I also wonder about using hi-quench, lower compression pistons to take advantage of the heads' high velocity while limiting detonation.

I have a question about the injectors. Assuming the 70 lb/hr injectors are rated based upon a factory fuel pressure of 13 psi, you'd end up with 110 lb/hr at 32psi. You could get the same result with 90lb/hr injectors at 20psi (111lbs/hr), and have some headroom if you needed more fuel later, couldn't you? Is there a benefit to running the smaller injectors at a higher fuel pressure?

 

You are thinking of static, which is simply a term for fully open. Asynch is a mode of in some instances desired operation.


Agreed

Sounds like a good idea, you should end up with about the same power, at a lower RPM, with more Idle vacuum.

GM TBI injectors are rated at 12 psi. I said 32, but meant 35 as I double check my math. I like the higher fuel pressure for two reasons, it keeps the system from vapor locking in high ambient temperatures (I have had the stock 12 PSI system do it numberous times in 105* temps especially due to the nature of a van engine compartment, it may or may not be a problem in a F-body that is not towing). Second, the higher pressure seems to give a better pattern and better atomization, which has the potential to decrease BSFC and cleanup the emissions. As far as power, there is really no difference either way. I just had a pair of 68 lb/hrs at 35 psi and know that they will operate there. The 454 injectors cost less based on the Autozone site I was just on, and should work just as well at somewhat elevated pressures.

 

I feel the same way alot of times.

Cams over 212* are IMPOSSIBLE to tune, shattered that myth.

Swirl Port heads are JUNK, they are clearly better than ported 416s under about 4,500 rpm, even in a hotter than stock setup. Ported they should equal the ported 416s.

People used to think that 320 FWHP was the limit of a TBI fuel system. 301 RWHP puts that number to shame and I was using 68 lb/hr injectors.

I have heard great things on the FSC truck board about going to long tube headers on a truck application. On the TBI trucks with 2 1/4" outlet manifolds, they were worth practically nothing on my 275 RWHP 305. Open headers made 301 RWHP, through the mufflers 275, through single exhaust, high flow cat, and single in/dual out flowmaster with 2 1/2" exhaust I made 272 RWHP with more torque down low. I got rid of the cut-out and therefore have no clue what would have happend with a cutout on that system.

Ultimate TBI mods have the potential to increase power, if you need the added CFM and supply the additional fuel, you will make more HP. I have datalogs on the old 355 to show this (90 KPA before, 98 kpa after, @ 5,500).

Gears depend alot on the modifications, tire size, etc. It is IMPOSSIBLE to suggest that one gear size is better than another for every possible combination. I had great track times in my 5,300 lbs beast with a 3.73 gear, P295/50/R17s, and a 2,800 stall. Traction plays a large part of it, as does power band. The stock TBI powerband is not high enough in the RPM band to effectively utilize the 3.73s. Dewey's very modified 5spd car on the otherhand might go quicker and faster with 4.10s.

 

So why do you drag me into this? Care to give the thread I made that statement in?

RBob.

 

Street engines frequently have BSFC of closer to 0.40.

Race engines frequently have BSFC of 0.5 or more, depending on how delibreately rich they run to avoid breakage of hard parts. Race engines also lack accessory parasitic losses (power steering, AC compressor etc) so they get slightly more power at the flywheel than the std passenger car does, and that reduces the BSFC because they have fewer parasitic losses.

BSFC is a measure of combustion efficiency and of losses.



HP is determined by both, not just by fuel flow as you have erroneously said.



At 12.5 to 1 air to fuel ratio, as defined by mass, the percentage volume displaced by the liquid fuel is 1.5%, as compared to the 98.5% volume of air. So your statement of the fuel displacing the air being significant, is false. I showed the math to prove the point in a post on TGO over a year ago.

Finally any carb or TB of MAF can be flowed at any pressure differential. The column height h of either water or mercury is related to the pressure measured (p=row*g*h) across the test article (pressure above the carb/TB subtracting the pressure measured below it).

Pressure*area = force

So if you have a 4v carb that has double the sectional flow area as compared to a 2v carb, then it's sensible (and an industry practice based on engineering) to half the pressure to maintain a similar force on the air passing through it.

A better practice would be to change the depression (column height) based on comparing the actual section flow area rather than just using a factor of 2 (because the area might not change as a factor of 2).

As for equating measured or rated flow to power output, a 48mm dual TB is good enough to flow enough air to support over 400 fwhp on an LT1 (a real engine). The flow section on that TB can be calculated and then the shaft and blade area subtracted from it (WOT condition, minimum profile). That can be used as the basis for estimating the power output from a smaller area 2 bore TBI knowing that 1.5% of the air volume is taken up by fuel. So getting hung-up on flow measurements isn't fruitful ---- 2 bore carbs and TB/TBI can flow enough air to make well over 300 fwhp, and 4bore versions can flow more air and make more power.

Running stock injector pressure, fuel flow will be the weakest link on a factory GM TBI -- it will limit power before the airflow will. Raising the fuel pressure (as GM did on the last of the 454 SS trucks) overcomes much of the fuel flow limit. When that happens, the small Rochester 220 TBI will be airflow limited somewhere over 320 fwhp. The power can increase beyond 320, but at diminishing gains due to the excessive flow loss (increased vacuum) around the TB.

The 454 TBI unit has 50mm bores so it overcomes the airflow limit by a good measure and no one yet has explored those limits here on TGO, AFAIK.

 

This is basically my argument as well. There's always all this talk about TBI limiting engines to certain power levels and that is why it sucks. There are guys making pretty big power on these boards with 454 TBIs and they aren't to the limit yet. But my head's in the sand, right? To be honest, I don't care enough to call Holley and ask them how they flowed it. If I have an engine that is going to push the limits of the 454TBI unit I'll try it out and see if it pulls vacuum up top in the RPM range. If it does I'll do something about it, if it doesn't, great. Simple as that. I just see no point at all to that being an ongoing argument on these boards and why people get so passionate about it when not a single person here has pushed the envelope of its flow capabilities.

Also, I remember posts from you back a while ago about using a Hot cam in your 305. You're saying now that you were told by the good tuners here that it coudln't be done, and citing their names as stating that, which I'd guarantee it was not said. These guys don't talk in "can't"s RBob and Dewey would not be guys to tell you that it cannot be tuned. I believe the argument then was that it should not be done. I think some were saying it may be too much cam, now I don't know what heads you were planning on running with it so it may or may not be too much cam. The concern would be whether or not YOU could tune it, not whether or not it coudl be tuned. People here try to help others with builds that they'll be happy with in the end and if they have no chip tuning capabilities then they're going to be advised not to run a HOT cam. Personally, if I had the head flow to back it up I wouldn't mind running one or any cam in that range, it wouldn't scare me to do it. But, you have to know how to tune it.

 

You guys do know holley didn't design their 2" tb right? It's just a slightly modified rochester, probably even made by rochester. The FACT is that no one has documented a case where a 2" TB will restrict a motor running TBI. You'll always run out of fuel first.

 

I think that people need to reread Ben73's past post about his 383 with essentially a 2" throttle body. No one here in my memory has since had such a buildup but this is being debated again. The info is there as to how far this has been taken before.

(Quote) Ben73

Pushing the limits of TBI

I think I am getting close to finding the true limits of the TBI system.
My 383's previous best was a 12.81 @ 107 mph with a few lame excuses like hot air and 3000ft altitude... It was running 2 x 90lb injectors at 15psi and seeing 90% duty cycle at the top end with the WBo2 showing a safe/fat 12.3-12.6 (commanded at 12.6)

I have just completed a cam swap and started tuning again. New cam is a comp 12-430-8 (280/280, 224/224, 560 lift w/1.6's and 110 LSA) I have got the VE's right again and am now working on the top end. With no changes to the fuel pressure, the WOT AFR's went to 13.0-13.3 and the injector were static, 100% + DC ! (commanded at 12.2). I was pretty happy with that as it means its breathing deeper ;-) I am putting in more fuel that before and it is STILL LEANER! Cool! ;-)

I have upped the fuel pressure from 15 to 16psi and its now showing 12.8-12.9 on the WB, still commanded at 12.2.

I will now go to 17psi and see if i can get the WOT AFR down a bit closer to the commanded AFR.

And the big question is, "is the idle suffering??"..
Not yet.. The PW's are getting short, but I think it will be ok.. The car is definately faster than when it ran the 12.8's and i will be going to the track asap.

I thought this maybe of some interest to the other guys who play with TBI.

I now have the 90lb injectors at 18psi, and they are still at 96% duty cycle to give me 12.6:1 at ~5800rpm! It likes the fuel! Idle is still ok with PW around 1.0-1.1msec..

BTW, I am only using 2" TB's.. This is a crossfire/x-ram setup, but its essentially the same as normal TBI.

As far as weight-shifted horsepower calcs go, it was pushing 320rwhp, now it looks like 360 according to the few online hp calculators i play with. (3400lb '84 vette)
They also guess at ~430 flywheel, up from the previous cam's 390... assuming 18% losses...

** don't flame me on the use of these calculators, i know that attempting to calc flywheel hp is a wild guess ;-)

(Quote)

 

I don't see how calling someone "knowledgable" and repeating what they said is "dragging them into this". Sorry if it offended you.

My CP doesn't have subscribed threads and PMs from two years ago anymore, and I'm not going to waste my time trying to sift through every post from 2002 to find it, but yes, you were absolutely one of the people who told me the LT4 Hotcam was too much cam for my 305. I'm pretty sure that was also one of the numerous times you've told me I should "put a carb on it" as well.

 

At the most basic level, an engine is simply an air pump. An engine willl move a specific amount of air through itself at any given rpm based solely upon CID and whatever restrictions there are in the intake and exhaust tracts. Regardless of the horsepower the engine makes, that amount of air remains the same. You can apply external power to rotate the engine, so it is making zero horsepower, and it will still move the same amount of air at the same rpms.

How much horsepower that air pump makes depends on the amount of fuel available and the efficiency with which it is combusted. Air affects horsepower as it is necessary for combustion, but the amount of horsepower made at any point in an engine's rpm range can vary wildly, depending on the amount of fuel available and combustion efficiency, even though the airflow remains the same.

 

First, I didn't say they told me it "couldn't" be done. I said they told me it would be "nearly impossible". Take the time to read what I said before you put words in my mouth and accuse me of lying.

Two years ago, the consensus from people in the know on this board was absolutely that cams over 218 duration were too much for a 305 unless the tuner was VERY experienced. I believe the LT4 Hotcam in my combination was described as a "nightmare" to tune by one of the numerous people cautioning against it (and it wasn't the heads). It came up over and over and over, not just in the thread I participated in. Dewey was decent enough to spend some time with me explaining WHY it would be so hard to tune, which is why I chose to go in a different direction.

Looking at recent posts, it would seem that duration number has gone up some. Whether that is because the good tuners got better, the average tuners got better, the software used to do the tuning got better, or some combination of the above, I don't know, but there are more people on here talking about tuning cars with cams of over .220 duration, and less people cautioning against it when the subject comes up today than there were two years ago when I was looking at doing it.

 

Then my suggestion to you is that unless you can provide the cite to my alleged statements you leave my name out of your posts.

RBob.

 

If IIRC, Rbob was running or perhaps still is, an Isky 280 Mega cam in a bored over 327. That is wilder than the Hotcam 305 combination that you would have been suggesting. I believe this was about 4-5 years ago or more. The duration on that cam is 232/232* @ .050. I have my doubts that he made the Hot Cam claim.

It might have been stated that for an otherwise stock L03 the hotcam was too much and that is IMO true.

Two years ago, I was running 214/224 @ .050 in a carbed 305 van engine, ported 601 heads, with a 454TBI, factory GM 454 TBI-carb adapter, and the stock aluminum GM Q-Jet intake. I ran it on a stock 305 caprice ECM with 350 injectors for a while with nothing more than a VAFPR. I would not recomend it, now that I have been prom tuning, but it ran well, had good power, ran cleaner, and got better mileage than the 200,000+ mile Q-Jet it replaced. The idle when stopped was somewhat unstable, but I didn't really care as most of my driving was on the highway at that time.

 

Double Post