dimented24x7

iTrader: (2)

So you've done all the basic mods like open air/CAI, LT1 cam, heads, exaust, posi, and maybe some minor tuning. Your car is now running mid to low 14's. Not bad...

Question is, where to go from here? What more can I do with my TBI?

The answer would be its now time to tackle some of the more complex issues of the TBI system. It sort of seems like alot of members do the basics but stop there and either just stays where they are or abandon their vehicle/induction system for something else.

We're hoping to get everyone (CFI guys included!) who has or have gotten good performance out of their efi to really chime in and hopefully we can get some good collection of info her to really help get more tbi vehicles into the 13's or 12's. Its out there, lets gel it all together...

***Rules***

Id like to have one new topic come up each week or when the present one has run its coarse. One of us (shifty, 90RS, or myself) will post the next topic to be covered in the thread. While the present topic is up, only discuss that topic!. It would be nice to maintain some order as not to just have a bunch of stuff jumbled together.

Also, play nice! Dont get carried away by giving your opinions on what can and cant be done. Just the facts... Try not to stray off topic. Anyone posting off topic posts is liable to have the posts deleted at a mods discretion. As always all the usual board rules apply.

90RS, or whomever, has a good point by adding the above clause... I guess I need a lawyer next time I do a thread like this

ShiftyCapone

iTrader: (7)

If anyone has a topic that they would like to be discussed so that they can either learn about it, or pioneer it with TBI let us know. The point of this thread will be to show the limits of the TBI ecm capabilites along with what can be done to them to go beyond those limits. This should put a lot of "turbo TBI" and "Super charged TBI" disscussions to rest.

dimented24x7

iTrader: (2)

For starters lets try this...

All good setups start with good planning...

Let us start off doing some planning for our future setup. Things that must be considered before a single dime is ever spent...

dimented24x7

iTrader: (2)

As tbis are available at flow capacities up to, or rumered to be up to, around 800+ something CFM, fuel will probably be your primary consideration...

There is some stuff you can do rather then jsut go out, buy this, that, and the other and hope you can keep it fueled.

An engines airflow capacity can be estimated. First, we know the motors displacement and its powerband. We'll use this motor for example: http://www.goautocenter.com/gen_ii_lt1.htm the one with the hot cam...

Furthermore, we'll say we have 90 pph injectors for a total of 180 pph of fuel... Can we feed it?

Lets find out...

At 6000 rpm, the motor will have filled all its cylinders 3000 times a minute, or 50 times a second. Remember that its a four cycle and it only fills four cylinders per revolutin. With a volume of 350 ci, it will have moved about 10 cu. ft. For you metric fans (including myself ), thatll be .285 cu. meters of air. This is the ideal case, though.

Volume = displacement x # of rotations/2

In reality, the motor cant entirly fill itself with air, instead it can only take in so much air. The ammount it can take in with respect to its overall volume is volumetric efficiency. This LT1 has quite a flat torque curve, so well assume, on the side of caution, that it has a VE of 95% Taking .95 x .285 will give ~.271 cu. meters of air. The engine is jsut like an air pump so we can treat it as such and use this formula:

Volume taken in per revolution = displacement of pump x volumetric efficiency

Ok, weve got a volume of air. Since our 90 pound per hour injectors are done in weight, lets find the mass of air for starters.

Air has a density of about 1.16 kg/meter^3 at cool temps so lets use that...

Mass of air taken in is .314 kg.

mass = volume x density

Turning to our injectors, we have a total of 180 lbs of fuel per hour, let us convert that to kg/second... 180 lbs per hour x 1 hour/3600 secs =.05 lbs a second

www.onlineconversion.com

...is alot easier then any stupid formula

the injectors can put out .0227 kg/sec.

Turning back to our air, we have .314 kg. of air. Lets say we dont have emmisions or have to run a cat so we can shoot for afrs of 12.5:1 this means for every unit mass of air we need .08 unit masses of gas. Mass of fuel needed will be .314 kg/sec of air x .08 = .251 kg/sec of fuel. We have .0227 kg/sec of fuel available. Uh, oh! Well be short on fuel at the engines peak power output! We'll need .055 lbs per second of fuel or 200 lbs per hour of fuel. No problem, thats about 100 pph of fuel per injector. This can be managed with pressure increases... Although one should try to maintain about 90% max duty cycle so about 220 pph of total fuel flow would be what one would want...

There are more considerations and catches that one would encounter in real life but lets leave those alone for now... My fingers are gettitng tired, anyhow...

edit: if I made any mistakes feel free to correct me.

Dewey316

Since i have a lot of experiance in planning

Some things to consider

RPM Range. Lets face it, we all want to run big lopey cams. Problem, big cams = big RPMs. not a great combination on a stock bottom end with over 100k miles on it.

Uses. I'm going to assume not everyone here has the luxury of a second car, so well it may not be an issue in a thread like this with high power dreams, and going all out. For most this needs to be considered, things like power-brakes, idle quality, etc. Not to mention the associated down time/tuning time of a very radical combination. Big high reving, high power motors, also need to get spinning. for the Auto guys this means a stall. take into consideration driving a car wtih a 3000+ stall in it.

Now, for planning things out. Do not try to do this on your own, there are tons of guys at every parts company, who's job it is, to help you pick the parts that will work together right. Don't be afraid to ask, The opinions on TGO are not the finaly answer, the guys working, for Comp, Lunati, Holley, Etc, know their products.

Now that i went off on a tanget (sorry guys, but i think it is importan information for people who will be reading this.)

Some plans that i would include in this build up.

Displacement, I would be leary of going to larger here, we need to work within our limits. I don't think a 383/406/434 is the right route. i think 350/355 is where it is at. I myself would not be opposed to going the 327 route. Get the 4" bore, less displacement = less air demand. That coupled with one of the best bore/stroke combo's available. And less friction due to the shorter stroke, might just be the ticket.

Single Plane Intake. We will get the biggest, bades intake possible with TBI going this route.

Cam, we will need something big. I'm going off the assumtion that our bottom end will handle some RPM. Idealy we will not be on a 305 anymore. Hot cam or larger here. Were going to need to open this combo up. I would shoot for something in the 230* + intake range. with as much lift as we can get.

Valve-train, often overlooked, but needed. We need to maximize where we can. Light weight components, and well matched springs are the ticket here. We need a spring that will support our RPM needs, but we don't want to much spring, that will drain power. Thing like good roller-rockers, lightweight retainers, and good pushrods will go along with this. Again, we need efficiant.

Heads. Again, we need something that can flow, but we don't need to go crazy, we are going to be limited in what our TBI unit will be able to do. I would think something in the AFR 195cc range is a good size to go with our build up.

Exaust. long tube headers, True duals, and an X pipe.

those cover some of the basics of the engine. So great, we made some horse power. Now we need to figure out how to get this car down the track in a hurry. (I skipped over turning, I WILL COVER THIS LATER IN ANOTHER POST, there is just going to be too much to type.)

My friends and I often talk about the 'Platform'. They remind me that i have the platform, i just need the power. This is KEY. We need to lighten, streghten, and miximize our ability to put the power to the ground, and make it stick. I'm going to touch on points here, but not go to in depth.

Tranny, Typical stuff here, 3000 stall minimum, we need to get this thing in the power, right out of the hole. Of course shift kits, etc are going to be needed.

Suspeions, normal stuff, sticky tires, SFCs, and maximize the springs/shock/geometry combo, to get us traction.

Weight. we need to trim the fat, fiberglass hood, shed the extra's we don't need. I would include, AC delete, etc in here.

Those are some basics, there is plenty there to kick a discusion off. I will post again when i have more time to type on on the actualy TBI related stuff. This is just starting planning the parts list of this combo.

dimented24x7

iTrader: (2)

If you have a big, heavy fully loaded thirdgen then big cubes might be an option to be considered. A 383 or some varient of a 400 will have more displacement, be more streetable, and easier to tune then a smaller displacement motor making similar power levels. Not only that but the higher torque output at lower rpms is just what a fully loaded street car needs. There is a catch, however...

Since a larger motor will demand more air then one of smaller displacement at a similar rpm (assuming they both have good volumetric efficiency) it will need more fuel to go along with that and with a two barrel tbi with just two injectors that fuel may not be available. Due to this, the larger the displacement, the lower the ceiling is going to have to be. While a 350 may be good out to around 6000 rpm with tbi, a 383 or 400 might only be able to be fueled out to 5000 or 5500 rpm and you should select your parts with this in mind. You definatly dont want to choose super hot cam and large runner heads designed to make power out to 6500 or 7000 rpm with big cubes. The fuel just wont be there.

cali92RS

Dont you think that a cam with 230* duration is a little much for this application? Thats gotta be a bitch to tune. Plus if your gonna be spinning it at high rpms (which u will need to do to reach its max HP), your running the risk of collapsing a lifter and valve float, especially with a high lift cam with fast ramp rates. At that point u almost need a solid roller cam, then u have to adjust your rockers once a month and they wear quicker.

I think in this case, less is more.

dimented24x7

iTrader: (2)

There are lots of things you can do to tune with a high duration cam with some overlap. Also, the lifter pump up wont be a problem if the motion of the valvetrain is kept in check and the valves arnt alowed to float. But, those are seperate topics. This is more planning what can be acceptably run with a tbi, not what the mechanical issues of the motor will be. The tuning aspect will be brought up in time. Just not now...

DM91RS

Just a thought...........but having a thread where people could list their combos (ie: all the parts, tuning done, gearing, etc) might be a good referance page to have. Could also have comments on how it runs, dyno and or et's if available and how hard it was to tune it..

Think this might help to prevent some headaches trying to get to the "next level"?

Dewey316

i really don't think it is too big. The more combos i work with with bigger cams, and EFI, the more and more willing i am to accept the idea of running bigger cams. Yes they take tuning, is it imposible? no. Its the overlap that kills you. keep a wider LSA, and keep the overlap from being too much, it should perform. Really we are talking power here. you just aren't going to make the power levels we are looking for with a small cam. Assuming we can fuel, and have a 2" bore TB, i really don't see why 400hp, or more is not doable. but you will need a cam capable of it. granted we are talking about 200+ pph of fuel to pull this off.

cali92RS

I know were talking about making big power here...but i thought we were gonna keep it realistic. I understand the only way your gonna make big power is with a big cam. But there are mechanical issues with that, mainly valve train issues, which i guess we wont address in this thread.

What is the biggest cam u guys have heard a TBI car run?

ShiftyCapone

iTrader: (7)

There was one or two guys with the ZZ4 and a few others with the Hot Cam. That is the biggest I can think of. Others have gone bigger but these guys actually tuned their cars and used the cam how it was supposed to.

Dewey316

which valvetrain issues do you wnat to address. There are ways to run a hydrolic roller up in the RPMs, AFR makes the hydrarev kit, there are many others, that with good studs, a stud girtle, etc. I'm taking this as a what could we do. the goal was to talk about potential sub 13 seconds cars. Frankly, that isn't going to happen without trying to push the known limits of what people run. Its going to require not thinking about what people HAVE done, but what we COULD do. I realise there are downsides to a large cam. That is also the reason i suggested a smaller displacement motor. So we can run a cam that will make better high RPM power. Torque is great, but what good does it do to spin the tires, we are trying to to come up with a combination that will get a car to the finish line first.

(please DO NOT take this argumentivly, that is not my attitude at all, I am really enjoying actualy having a discussion on this. And talking about things like how big of a cam is too big. We rarely get a chance to do this, and have it remane a good discusion.)

John

cali92RS

I wasnt at all taking this argumentively. I know about what could be done to make a hydraulic roller work, but in the kind of engine that we are talking about (ie not very streetable), it would be better to run a solid roller. You can run much faster ramp rates (higher lift with lower duration), which allows tuning to become easier.

In fact, there is a custom cam that i was looking at that i think would be a beast in this situation. Its like the xtreme energy 276 cam with 224*/230*, but instead of .503/.510 lift, it has .567/.584 WITH 1.5 ROCKERS . Now thats some really fast ramp rates, which allows you to get the power and torque you want without having to rev it pass 6000. Its a proven mid 12 sec cam in a TPI with the lower lift, and its gotta be a low 12 sec/high 11 sec cam with the higher lift lobes. My question is how would a proven 12 sec cam with a super ram translate to a TBI application.

As far as The ZZ4 cam or hot cam, those are alright mid range cams, but thats not what were talking about.

ShiftyCapone

iTrader: (7)

They are largest (and tuned) cams that I know of in a 305 TBI to date.

cali92RS

So are we limiting this to a 305?

ShiftyCapone

iTrader: (7)

No not at all. You were asking about large cams in certain TBI applications. I was just naming the 305 TBI ones that I knew of off hand. As for the largest in any TBI application I think has yet to be found. I think r90camarors may have one of the largest tuned cammed combos in his 383 at this point in time.

cali92RS

I think this is a good jumping off point...what do you guys think is the biggest cam u can run with a properly tuned TBI, for HP, not low end torque. Also, how can we apply proven combos from other inductions and apply them to TBI.

Dewey316

I don't think a solid roller is out of the question. I would agree it is the way to go. My good friend has a 355 with ProTops, HSR and a Big Solid roller (240 something intake duration) .565 lift.

He is running a MAP computer system. It runs great, drivable, etc. It idles a hair rough, but that is to be expected. he is also running a 48mm TB.

Here comes the problem

He runs 30pph SVO injectors with 42psi (about 32pph) and going static at 6k. That would equate to using over 120pph injectors in a TBI unit. It is all going to come down to fueling. I think 120pph should be doable, if the big holley injectors can handle say 20psi of fuel pressure, then the fuel flow is there. The airflow should be there, then it is all a matter of getting the rest of your ducks in a row.

dimented24x7

iTrader: (2)

To me this is a good combo for those who still want around 375-400 HP and want to be able to drive the car regularly. https://www.thirdgen.org/techbb2/sho...hreadid=230966

One of the things I really dig about it is that because the cam is relatively mild, the powerband is right there at lower rpms. There really isnt need for steep gears or a way high stall as the motor is ready to go as soon as you hit the gas. Can still have a mild gear like 3.23's so it can be comfortably driven down the highway at moderatly high speeds like 80-85 mph without having to wind the motor. This would be something I would be open to using, but with maybe a hair more duration at the intake. Definatly would be nice to have my cake and eat it too. A stock trim car that is not only friendly and mild on the street but is still good for at least very low 13's. Maybe even low 12's or less if its set up right.

dimented24x7

iTrader: (2)

Of coarse, there is alot to say for planning on running a hot setup... There are alot of challanges that one has to overcome to really get it to run great and not just good and doing so can be quite rewarding. But, milder setups can definatly be put on the menu for those who dont wish to get deep into the ***** of tuning and tweaking an efi system from the tbi to the ecm. Althogh I kind of like trying new things. Tickles the brain a bit...

cali92RS

What about the holley 4bbl system (holley 900?)

dimented24x7

iTrader: (2)

I posted some links to that in the new to tbi sticky. There are some issues with that, too. Also, last I heard they where selling new for nearly 800 bucks a pop.

dimented24x7

iTrader: (2)

Quick note on the holley units. They presently use oem replacement FWDer injectors. I did some research and found out the info and posted it in this thread https://www.thirdgen.org/techbb2/sho...hreadid=239966

I would highly recommend not spending any of your nickles and dimes on a holley unit. In addition to a chinsy tbi base, they also use small injectors that have the same old nozzle design as all the regular injectors used in our cars. Nothing special about them. On top of that, there are internal o-ring seals in at least standard TBI injectors so even if the injectors can still function at high pressures (obviously youd need way more then 20 psi), they may blow out internally and spew fuel everywhere. I have no idea what they can truely be safely taken to so I guess one would have to try and tell...

cali92RS

Do TBI's like more or less duration cams than TPI's? I would think they would like more because of the leeser amount of air and fuel.

EDIT by dimented24x7: Id like to keep the discussion centered on tbi

dimented24x7

iTrader: (2)

Well, the duration that can be run is really only dependant on how high one can properly keep the motor fueled, and to what ones tuning abilities are and to what level one is willing to make changes to accomodate it. Obviously the more overlap the more the vacuum level and stability will be affected so keep LSA in mind as well.

cali92RS

LOL...not one for sarcasm ey

Anyway, I know about cam tuning, overlap, LSA etc. Im just trying to draw some parallels from TBI to other inductions... Would a proven 12 sec cam for a TPI, stealth ram, super ram, mini ram etc, also be a 12 sec cam for TBI? Thats the main question i am asking.
The problem is that there arent a lot of high performance TBI's out there to pattern after. So i was thinking if we can take proven cams from other inductions, and work off those (ie increasing LSA, decreasing overlap, increasing lift etc), it might be helpful.

dimented24x7

iTrader: (2)

Resonance issues aside with some of the induction systems above, what works with one type of system should work equally well with another. My line of thought is that fuel is fuel and air is air. So long as you have the right ammount of fuel, air, and spark itll make power.

Oh, I sent you PMs about that. Check your inbox.

dimented24x7

iTrader: (2)

That is why this thread is here. To get some good info in one place so people have more of what they need to help them make informed decisions as to what to run.

seanof30306

iTrader: (4)

Great thread. Want to bring up a few "first step" planning issues.

First, I think a 383 or 400 with parts selected to make max power at under 5500 rpm would be the best choice. less rpm = less required airflow. I ran a bunch of simulations on this a year or so ago, and am pretty sure i remember finding a 400 needed less air at 5300 rpm than a 350 needed at 6000 rpm. Building a lower-revving combination has the additional benefit of being easier on the bottom end. When you can pick up a 383 shortblock from wheeler motorsports for under 1400 with hypereutectic pistons, arp rod bolts, cross-drilled and chamfered crank, etc., it's hard to pass up.

The question that needs to be cleared up before anything is done, however, is how much air the various throttle bodies available to us flow at 1.5" hg. Every formula for calculating airflow needs is based upon airflow at 1.5" hg, and, until you have that, I think it's crazy to start buying other parts. I can't believe someone on here doesn't have access to a flowbench. I think we all need to make getting access to one a priority, then lending the various throttle bodies available to the person with that access. That's a sticky we need!

Beyond air, fuel is an issue. I'd always thought airflow would be the limiting factor, but I was talking to Scott at CFM Technologoes not long ago and he raised a very good point. With only two injectors feeding the engine as opposed to the eight injectors in an mpfi setup, TBI injectors are forced to cycle much more quickly. You can easily reach the mechanical limit of the injectors to open and close quickly enough to keep up with the engine. In addition, when you raise fuel pressure, you actually have a negative effect on the injector's ability to do that, as more pressure = greater line resistance for the injector to work against. Also, the bigger the injector, the slower the cycle rate. He also mentioned the computer's ability to provide the firong pulses. I was riding in the car at the time and wasn't able to take notes. I need to follow up with him on this.

Those fueling issues would also seem to dictate a bigger cub/lower rpm combination.

cali92RS

I agree with sean on this on, i think a 383 would be a good block to start of with. I also think it would be a good idea to keep the cams powerband between 2000-6000. Lunati makes a nice cam 230/238 , .565/.565 w/ 1.6 rockers on 110* LSA. You can get that ground on 112* or bigger for ease of chip tuning. And that would give u power all the way up to 6000 rpm in a 383 (or 6200 in a 350). If you couple that with AFR 195 heads, 3000 stall, plenty of suspension/chassis work, and a 454 TBI w/ the right injectors, and you should be deep into the 12's N/A.

dimented24x7

iTrader: (2)

One thing to keep in mind about 383s is that they will have higher airflow demands then motors with smaller displacement. The added stroke (and the overbore) means that with each intake stroke a piston can sweep out a volume of ~48 cu inches where as a 350 can sweep out a lesser 44 some odd cubic inches.

The real thing that makes more displacement attractive is the increased power potential, but the fuel capacity has to be up to the challange. Another added benifit is that the same performance parts on a larger motor will be more streetable then those on a smaller one. The cam I have in my 350 is actually a decent cam in a 283. Although its arguable as to whether the 283 would be able to do a better job in a large car.

Always bear in mind that the larger the motor, the narrower the powerband will be when the fuel flow is fixed. Itll still make good power, its just that the range that youll set it up to make the power will be at lower rpms then a smaller displacement engine would be.

As for teh airflow, holley says they flow their tbis @ 1.5 inHg. Someone also flowed various CFI throttle bodies and they seemed to varify that the holley actually flows around 670 CFM. This is believable as there isnt anything blocking the airs path in the bores like there is with some carbs.

seanof30306

iTrader: (4)

wow, that seems like a pretty big cam for an engine that tops out under 5500 rpm. also, the afr 190 heads have 195cc intake runners. i think that's a little extreme for the application we're discussing. if you look at the edelbrock e-tec 170s, they flow as well as the afr 195s up until .550 lift. on a street engine, it's the mid-flow numbers (.300-.400) that make all the difference. additionally, the etecs' 170cc runners should offer better low end torque and crisper throttle response than the afr 190s. vortecs, for example, have 170cc runners, and are good for up to 450hp.

and on the holley tbi airflow supposedly being at 1.5" hg? that all started about a year ago with one guy posting he'd spoken to holley and had been told that their 670 number was at 1.5" hg, and another guy following up with a link to airflow tests on crossfire (1bbl) throttle bodies, saying each of those throttle bodies is essentially a tbi throttle body cut in half.

i'd spoken to holley before that post, i emailed holley after that post and had a long conversation with one of their engineers after this came up again several months ago. each time, holley gave me the same information: all 4bbl carbs and throttle bodies are flowed at 1.5" hg, all 2 bbl carbs and throttle bodies are flowed at 3" hg. each time, holley stated this was not only their practice, but an industry standard applied by all oem and aftermarket manufacturers.

since that conversation, i've also asked barry grant carbs, cfm technologies, turbo city and edelbrock. all replied with the same message: 4bbl = 1.5" hg; 2 bbl = 3" hg.

the holley engineer gave me a conversion formula which he said was "pretty accurate." it's:

CFM @ 3”HG X 70.7% = CFM @ 1.5"HG

EXAMPLE:

670 CFM @3”HG X .707 = 474 CFM @1.5”HG

if you decided to go with a 670 holley and used that formula, you'd find the holley will not support a 350 @ 6000rpm. The formula for calculating that is:

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

EXAMPLE:
350 CID X 6000 RPM = 2,100,000 / 3456 = 608 X 85% Volumetric Efficiency = 516 CFM

here's a link to a calculator for that: http://www.csgnetwork.com/cfmcalc.html

using that calculator, a 383 torque monster topping out at 5000 rpm would only need 470 cfm. if the power maxes out at 5500 on that 383, it would need 518 cfm.

Regardless, the challenge is still to learn how much air the other throttle bodies flow. no one knows the exact cfm ratings for the small block and 454 tbis, mush less the ratings for them after they've been bored out, ultimate tbi mods, etc. i'd bet the sleeved-out 2.2" big throat throttle body flows more air than the holley, 670 .... but HOW much more it flows is critical.

Then there's fuel. The formula for calculating fuel needs is: Injector Size = (HP @Flywheel X BSFC*) / (# Of Injectors X Duty Cycle**)

EXAMPLE:

(400 HP X .45 BSFC = 180)

(2 Injectors X .9 Duty Cycle = 2.222)

180 / 2.222 = 81.081

* BSFC = Brake Specific Fuel Consumption, how many lbs of fuel an engine will consume per hour. It shows how efficient an engine is at converting fuel to horsepower.

BSFC of .50 for low to medium performance street engines

BSFC of .45 - .40 for performance engines with good heads

(richer air/fuel ratios raise the BSFC)

** Duty Cycle = The maximum amount of time you want an injector to be open. Under most circumstances, you don’t want an injector to be open more than 90% of the time.

according to that formula, a 400 hp tbi engine would need two 80 lb. per hour injectors. however, this doesn't take into effect the injectors' mechanical ability to feed an engine at higher rpms. the number of times an injector must open and close is in direct correlation to rpms. since tbi injection systems use only 2 injectors vs. an mpfi system's 8, the individual injectors in tbi must not only flow more fuel than mpfi injectors, they must also open and close more frequently at any given rpm than mpfi injectors. i don't know how to calculate that yet, but, according to scott at cfm technologies, it's a big issue. he said when you rev the engine past the injector's ability to perform, it simply skips the operations it can't mechanically perform, putting NO fuel into the engine during that cycle. That causes over-lean conditions at the worst possible time.

by the way, if you're wondering what effect raising fuel pressure will have on injector flow, here's a link to a calculator for that:

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

dimented24x7

iTrader: (2)

For some reason people always seem to get hooked on air. Although the tbis only have two bores, they can be two very large bores. The bores of larger overbored 2.2" tbis have nearly 80% of the cross sectional area of four of the 1.75" bores of the 4 barrel holley EFI throttle bodies. Incedentally, they are rated at 1000CFM. Assuming one could scale the flowrate it would equate to around 800 CFM. Since its supposed to be rated at 1.5 inHg one could assume that the 2 barrel unit would have a similar flow rate. This would be a reasonably safe assumption as the two barrel tbi has a lower ratio of bore circumferenc to cross sectional area, meaning that boundry layer effects will be less with the larger diameter bores.

The thread you reffered to is here https://www.thirdgen.org/techbb2/sho...hreadid=194984 The flowrates where done @ 1 inHg

Assuming they did the tests correctly, I think it would be safe to use this data as a reasonable substitute. The internal design of the bores is nearly identical to those of the standard two barrel units and I cant see loosing HUGE ammounts of flow because the bores are next to eachother.

Im also feeling the next topic coming on...

dimented24x7

iTrader: (2)

Eventually what happens is the injectors jsut stay wide open when the DC gets too high. The restoring force of the springs that seat the pintle cant seat it in time and it jsut goes right back to where it was before when current flows through the soleniod coil or it jsut plain stays on the whole time if the DC is nearly equal to 100%. There was an interesting thread over on one of the GN boards as to what happens to an injector as the DC increases. A memeber benched an injector and recoreded the flow rate as the DC went up. Some speculated that the injectors would get crazy when they approached max DC but really all there was was a small rise in flowrate before the injector settled at its static rated flow. Although no reason was given for why this was Id speculate to it being caused by the pressure front that forms beind the pintle as it touches down on its seat. The next injector firing occures before this can dissipate so in effect its like increasing the fuel pressure.

BTW, there is an injector firing for each reference pulse recieved by the ecm. The injectors alternate firings in normal operation so each tbi injector fires twice per revolution. This isnt quite as much of an issue at WOT as it is at idle. The PWs can ger real short with a big set of injectors.

dimented24x7

iTrader: (2)

Ahhh, found it... Here are some flow tests ive looked at previously. They where done @ 2 inHg. http://dtcc.cz28.com/flow/ I cant vouch for their accuracy so we'll have to take them at face value. The data for the holley 4 bbl efi tbi looks about right, though. Oh, and they also have conclusive proof that an airfoil really does work (a little bit...).

dimented24x7

iTrader: (2)

Another thing to consider is the intake used. I have an edel. performer thats probably not much better then a stock q-jet intake. GM evidently thought that upwards of 780 CFM on some of their q-jets was needed on a dual plane with a small plenum volume. I noticed with my stock tbi that I was pulling some serious vacuum (nearly 3 inHg according to the MAP at high rpms) since there wasnt much plenum volume below to buffer out the effects of the cylinders taking in air. Of coarse my larger 670 works much better, although I now have the problem of too much air. Most of the time with it pegged wide open, there will be straight atmospheric pressure up to around 2k.

seanof30306

iTrader: (4)

dimented,

you are clearly much more knowledgable than i on the mechanical engineering aspects of the issue, but i think you're missing the point.

it doesn't make sense to design an engine to make power significantly past the point your induction system can support.

the only reason the mercury levels the flow rates are done at is relevant is because the formula for calculating the airflow necessary at any given cubic inch/rpm point requires airflow at 1.5" hg. knowing what the airflow requirements are is, i believe, critical in every project, but especially so in this one, where you said:

"For starters lets try this...

All good setups start with good planning...

Let us start off doing some planning for our future setup. Things that must be considered before a single dime is ever spent..."

i couldn't agree more! i've been doing that research and planning since i bought my car and joined this board more than a year and a half ago.

now, obviously, there is another method of calculating airflow needs, as automakers have been building engines with 1bbl and 2bbl induction setups for decades, and their engineers are quite thorough and would have carefully calculated the airflow requirements of each combination, but since the only formula for calculating airflow that i'm aware of requires airflow at 1.5"hg, then airflow at 1.5"hg is the only airflow figure that is relevant. if the crossfire injectors were flowed at 1"hg, then their flow numbers have no relevance, either.

again, it's not an issue of whether it flows more or less air, it's an issue of how much. my ideal combination woud be a 406 (or larger). i have a lot of experience with big cube small blocks in carbed applications, and am an absolute believer in the "there's no replacement for displacement" theory. in a tbi application, however, induction is going to be the limiting factor, and i'm not going to make the decision between 350/383/406 till i'm absolutely sure i can put enough air and fuel into the engine to make it work. now, i could build a 383 and bolt on progressively bigger throttle bodies till i find that limit. if i don't find it with the 383, i could tear it out, bolt in a 406 and go through the whole process again, but that might be a bit expensive. it makes a lot more sense to me to use the tried and true engineering methods in place for decades to calculate my needs/limits BEFORE i start throwing money at it. I've used the airflow and fuel flow formulas from holley in a number of carbed applications in the past and have always been quite satisfied with the results, usually running less carb than my friends with similar setups and running faster. i'll trust them here, too.

how many people on here have bought a 670 holley tbi for their 383 or 406 because their calculations showed them they needed 650 (carbed) cfm to support their combination, only to find out it fell on it's face at 4800 rpm? when i first signed on here, i went back and read all the tbi archived posts to familiarize myself with a new, unfamiliar induction setup. i saw numerous posts from people who'd made that mistake, and resolved to not make it myself.

in order to properly calculate the airflow needs of any given combination, we're either going to have to find out what the various throttle bodies available to us flow at 1.5" mercury, or come up with another reliable formula for calculating airflow needs at 3"hg. that's all there really is to it.

dimented24x7

iTrader: (2)

Really there not irrelevent alltogether as the flow at the pressure drop gives an indicator of the flow capacity of the system. Just because one system may have been done at a pressure drop of 28 inches of water, which is ~2 inches of mercury doesnt mean all the data is meaningless. Its not, there it gives one a fairly good idea of what the flow capacity of the tb being used. At the lower pressure drop of 1.5 inHg the flow would be less but not so much so that all the data is completly useless. All the pressure means to me is that if I was using an item that, I could expect to see a loss of 2 inHg of pressure going across the tbi into the manifold at an average flow rate of XYZ CFM.

All it is is a measure of how much flow will be realized when a certain pressure drop (potential to induce flow) is applied. We could have the convention be 10 inches of mercury, although the pressure drop would be so large to realize the rated flow that it would seriously hamper performance. I wouldnt get too hung up in the details. The 1.5 inHg to me is just a yard stick by which to measure by. The farther away from 1.5 inHg, or whatever it is in water, PSI, pascals, fathoms, or whatever they choose to test at at, the less I can trust their data as I dont have an iron clad way to see what the flow would actually be in terms of 1.5 inHg like everything else is measured in. But, I think that values in the neiborhood are acceptable. I see that they realized a flow rate of 575 CFM @ 2 inHg pressure drop from a stock tbi. That would tell me that at around 1.5 inHg pressure drop I could expect around 460-480 some odd CFM in carbeurator terms, which is overly small for anything other then a stock V8. As for them testing at lower pressure drops then 1.5 inHg. Ill definatly take that data if the tests where performed correctly . That means that if I was thinking in terms of 1.5 inHg and selected the same rating at 1 inHg I could rest assured that it would be equal or greater in flow to what I designed for as it realized that flow at a lower potential then what I had chosen.

Also, one really cant make assumptions about how the holley tbi stacks up to a similar setup with a carb by offhand acounts as things like the motor being properly fueled, the intake used, heads, intake, etc. all come into play. The holleys have very small injectors so if I was spinning something way up I wouldnt be at all surprised if it fell flat on its face from being lean.

So far what the data tells me is that Ill probably have enough airflow if I choose the largest tbi available. Only having 200 pounds per hour of fuel is going to be my controlling resistance as to how much power I can make.

dimented24x7

iTrader: (2)

Actually, I have done some tests with airflow in a lab. Some of the ideal formulas are actually quite close to what the actual values will be so long as teh airflow is sufficiently far away from the speed of sound. Although the mean airspeed through a holley 670 flowing at its rated capacity will be at a blustery 170 mph, its sufficiently slow that formulas that make idealized assumptions could be used when exploring things.

dimented24x7

iTrader: (2)

The formula for estimating what the flow capacities will be between different pressures is given in the linked thread.

new_flow = old_flow*sqrt(newdp/olddp)

For stating what the flow rate would be in 1.5 inHg for something rated at 2 inHg, we could expect to have only ~86.6% of the flow

Doing the same for something rated at 3 inHg, we could expect to ahve only ~70.7% the flow, sound familiar?

seanof30306

iTrader: (4)

i believe your assumption that airflow being "close is good enough" is dead wrong. again, i'm not nearly as knowledgable as you on the theory, but i have significant experience.

on the last 406 i built, we calculated the cfm required as 689. we put a 650 holley double-pumper on it, but it'd fall flat on it's nose at around 5600 rpm. the next size up from holley at that time was 750. tried that, worked with an excellent tuner, but still couldn't get either carb to work right. 650 launched great, but no big end. 750 ran like a monster on the big end, but had poor short times and crappy throttle response in everyday driving. neither combination would run faster than a 12.70. if i remember correctly, the 750 ran a best of 12.71, while the 650 ran a best of 12.78.

at the time, barry grant was selling modified holley carbs. he hadn't begun manufacturing his own yet. i heard about a 700cfm holley he was selling and bought one. it was almost dead on, right out of the box. after one jet change, we got the car running consistent 12.40s, and it had better short times and throttle response than with the 650!

now, if the formula for converting airflow at 3"hg to airflow at 1.5"hg the holley engineer gave me is correct, 670 cfm at 3" = 474 cfm at 1.5". that's a difference of 200 cfm! in my experience, a much smaller difference in airflow can make a big difference in the way a car runs. in the case of my 406 chevelle, 50 cfm meant almost 3/10s. that's huge. I've seen differences of 20 or 30 cfm be worth lots of horsepower and torque on an engine dyno.

at their most basic level, our engines are simply air pumps (motivated by explosions). at some point in the process of moving air through that air pump, there is going to be a "bottleneck", where the combination's airflow limitations will be reached. while that bottleneck can be different in virtually every situation, in the case of an "extreme" tbi, it will surely be the throttle body. having as precise an indication as possible of exactly what that limitation is is critical.

as an example, i go back to your suggestion of afr 195 heads earlier. the more i think about it, the more i think it would be a mistake. those 195cc intake runners are designed to make power to 7000 rpm. even on a 355, it's doubtful any tbi throttle body could flow enough air to support that, so buying those heads when there are less expensive choices with 170 cc runners and comparable .300", .400" and .500" flow numbers would, i believe, be a mistake. it's the reason i walked away from a GREAT deal on a set of fast burns last week. if 195cc runners are too much, what would 210 cc runners be?

on the fuel issue, i'm not sure about the injectors staying open when the rpms outpace their ability to cycle. again, i'm nowhere near being in your league on the engineering, and scott at cfm technologies could be wrong, but i remember him saying when the pulses were coming faster than the injectors could open and close and they caught the injector on the "close" cycle (but before it actually closed), the injector completed the closing cycle and stayed closed until it recieved another pulse. I'm almost positive i remember him also saying something about the ecm's inability to provide accurate pulses at high rpms. regardless, if the injectors are cycling twice per revolution, that means they're having to open and close 12,000 times per minute at 6,000 rpm. that's a lot, especially when you consider an mpfi injector fires once every-other revolution. that's 3,000 times per minute at 6,000 rpm.

i'm thinking this mechanical limit may be what ultimately sets the upper performance limit for tbi. maybe this is why all gm tbi applications are DESIGNED to fall on their face below 5,000 rpm, and they continued to use tbi in low-rev/high torque applications for so long while using other injection methods for performance applications.

you mentioned 200lbs per hour of fuel being a hard limit, but my buddy's 351 mustang makes 344 rwhp with 26lb svo injectors, running at their recommended fuel pressure. that calculates to well over 400 flywheel hp with only 208 lb/hr fuel.

seanof30306

iTrader: (4)

yes, it does, giving further credence, in my mind, to everything that holley engineer told me.

it also makes my point about being in the dark with so many of our choices. we KNOW a 670 holley tbi is rated at 670 cfm @3" mercury. with that formula, we KNOW that works out to 516 cfm @ 1.5".

we have NO definitive data on how much air the stock small block and 454 throttle bodies flow, however, much less how much air ones which have had the ultimate tbi mods flow, even less how much air the bored out units available flow. in order to properly put together induction systems for our engines, this is data we absolutely need.

i again stress the need to get access to a flowbench, gather examples of the various throttle bodies available to us and test them. once done, it can be published on here and all will have the information.

Dewey316

I'd bet money, that the only TB that flows more than the 670, the 2.2" modified 454. I bet even an ultimate TBI 454, is either just equal to, or slightly less flow than the holley.

seanof30306

iTrader: (4)

i agree, although the 51mm tbi the extreme-efi guy on ebay sells might, too.

i still believe we need to know, though. could you imagine considering a carb or tpi throttle body without knowing the airflow? you only see that with tbi.

Dewey316

well, i don't see the point in knowing the actualy flow of anything less than the 670, we know it is not up to the task of anything even descently extreme.

seanof30306

iTrader: (4)

actually, dewey, you're absolutely right. i sorta painted myself into that corner when i "proved" that a holley 670 was too small for the application we're discussing, didn't i?

Dewey316

Whats interesting about those numbers though.

Is that guys like prevost are running good times, with a 350, and the 670. and producing more HP than they should with 516 CFM of airflow.

Now, get ready to start rethinking our airflow theory's

My 305, pulls NO VACUME at 6500 RPM. with the stock TB.

According the above equation, at 6500, my 305 'should' require 487CFM, that is almost what we are saying the 670's limit is.

BronYrAur

iTrader: (1)

I'm thinking along those same lines Dewey. I can't see how the Holley 670 can possibly flow only 516cfm if so many guys are using them on big motors.

Offhand, Prevost is running good power out of the 350HO with a 670 on it, and r90 had his beefed up 383 trapping around 107 and it wasn't even near fully tuned. I know he spun that motor up to 6000 too. If a 670 was enough to feed that 383 up to 6000 I would think it flows more than we're giving it credit. He was also running lean on top IIRC that tells me that the air was there to use at 6000 but the fuel was being delivered.

I also remember Grumpy pointing out a post about injector duty cycle (I think it was actually the post that dimented posted a link to). It seemed to show that once your injectors go static (open all the time) the fueling accuracy doesn't go all that far off from the rating. I really think that a high pressure 90pph set of injectors can support tons of power. Many have shown that they will take the pressure and still operate.

I believe VA454ss posted a while back that he had a friend that worked at GM and they tested the TBI injectors at pressures up to 70psi and they still didn't blow out or malfunction!

I'm torn between what's being said about head selection, I would like to say just go with a proven great flowing head like the AFR's but I see where sean is coming from with the 170cc heads. I think he may have a point there and they might actually make more power. I'd like a set of those Edelbrock E-tec 170's, those look real nice.

cali92RS

I've heard good results from E-Tecs. Of course they require a vortec manifold. I would have absoultely no problem selecting E-tecs over AFRs (except im in cali so i need to be smog legal). However, there is the issue of the size of the intake ports, 170cc vs. 200cc. Personally, I think with a 383, you gotta go with the 200cc heads, they have way more potential up top, and you are only losing a small amout of low end torque. And I think a small loss in low/mid range torque is alright because youre gonna have enough to fry the tires as it is.