have some money and want to do headers and intake. can the stock fuelpump and tbi unit feed the extra power plus the mods i allready have? if it won't, how much power can the Turbo City TBI manage. I would go with the holley 760 but I am afraid that is to much and better suited for a 350 (am i wrong on this one?) I want these mods soon but not if I can't the beast. How far will it go...pump and unit?

------------------
1990 RS 305 TBI T-5
.5" turbocity spacer
Summit 14X3 OpenElement W/k&N
Hooker 3" Areochamber
MSD - Wires, Cap, Rotor, Coil
Bosch Platinum +4 plugs
Metallic Red w/28,000 Pampered miles
(Still have the original wiper blades)

 

Holley tech support once told me that the stock TBI can support around 260 HP. They never mentioned what became the restriction after that. I've heard it flows about 500 CFM, but i'm not real sure about the CFM/HP equation so i don't know if thats the bottleneck. Maybe past that the fuel injectors are maxed out, that would be my guess anyway. 350 injectors are always an option i guess, but that probably requires some chip tuning. I wouldn't call myself an expert, but theres a few around here thats for sure! Nobody else posted yet so i figured i'd at least give it a shot.

So i gues the answer would be yes, BTW i plan on doing the headers and intake after my gears, i'm interested to see what kinda luck you have with it.

------------------
88 Camaro (not an RS, or an IROC, justa camaro.)
305TBI/700R4/2.73
14" Open Element and Flowmaster 80 seires

Next up: headers and gears

[This message has been edited by HrdRockA4305 (edited July 17, 2001).]

 

I would say 350 tops, with bigger injectors and a lots of chip tuning. however, i bet youll have some vacuum left at wot. so it would be a restriction, and you might as well use something larger if you want more than that.

 

i will stick with the turbo city one. once i get heads and cam i want to make sure I can feed it. does nyone have any coments on the turbo city unit? good? bad?

------------------
1990 RS 305 TBI T-5
.5" turbocity spacer
Summit 14X3 OpenElement W/k&N
Hooker 3" Areochamber
MSD - Wires, Cap, Rotor, Coil
Bosch Platinum +4 plugs
Metallic Red w/28,000 Pampered miles
(Still have the original wiper blades)

 

FYI, I got 310+hp pretty easily out of a 350cid with the small OEM GM TBI unit, fuel pressure change+, mellow Comp XE250 cam (110deg lobe sep, 206/212 deg), OOB Vortec heads w/good springs and a lot of PROM tuning AFTER I ran the engine on a dyno with a HEI/carb to get best spark/fuel/EGT data... 400lb-ft of torque, too. Enough for my Wrangler, that's for sure. 5300-5500rpm finish, though.

For a race car, will need to get more rpm and high-rpm torque in order to get HP.

[This message has been edited by FastBroker (edited July 18, 2001).]

 

i am putting somewhere in the 225hp to the wheels range(deduced from track time and speed) which means i am making about 270 at the crank, and i can tell you there is a lot left in it. i will find out how much when i do the cam in the next week or two. i think it can get into the 325-350hp at the crank range pretty easily.

lata
tim

------------------
91 Camaro RS-LO3,Auto.
14.209@95.46mph
Best 60' 1.917
Check Out The East Coast F-Body Nationals Home Page
www.geocities.com/njspeeder

My MAFB.ORG Home Page
www.mycar.net/mafb/registry/detail.cfm?id=299

DSI Racing Home Page
www.geocities.com/foff667

 

nj speeder,

are u still using the stock tbi unit, or have you moved on to better things like a 454 tbi, or holley's?


------------------
1990 RS 305 TBI T-5
.5" turbocity spacer
Summit 14X3 OpenElement W/k&N
Hooker 3" Areochamber
MSD - Wires, Cap, Rotor, Coil
Bosch Platinum +4 plugs
Metallic Red w/28,000 Pampered miles
(Still have the original wiper blades)

 

Do NOT buy a Holley 670cfm over a GM 454-type 670cfm. Holley's injectors are inferior to GM's and cannot take FP increases as well, should you need it for more power later.

 

Didn't they fix that problem already?

------------------
Pat Hirsz
www.iit.edu/~hirspat/MyPage2.htm
88 305TBI
Mods:Hooker Aerochamber 3" exhaust, no cat,SLP 1 5/8" headers and y-pipe March pullies, no smog, 180 thermo,
14x4 K&N, 3.42 gears(open), Ultimate TBI Mods,AFPR,MSD(ignition,coil&wires),Edelbrock TBI Manifold, 190ltr/hr fuel pump,
Eibach springs with KYB's all around,
Harwood cowl hood, Z-28 wing, fresh paint(black)
120,000 miles, 5spd, T-tops
0-60mph-7.2s-Gteched

92 RS, 305TBI, auto, 3.08 gears, 180 thermo, glasspack (no muffler)

 

Nope.

 

ive seen a new holley unit, actually somebody here bought one too. dont remember who, or where i saw the pic. but when i talked to hpp, they said they were switching over, but anybody that got a newer style was lucky, because their dealers are supposed to sell all of their old style ones first. But, to my knowledge they have switched over to our injectors.
well, or maybe they just got rid of the stupid round injector caps and went with a differnt style, but are using the same injectors. damn, I CANT REMEMBER.

well, one of those two things.

 

I'm doing the following off-the-cuff, and I think I have it right, but correct me if I don't:

Fuel limit:

hp = (#injectors)*(#fuel/hr)/BSFC

hp = 2*(65lb/hr)/.50 (lb/hr/hp)
= 130/.45 = 260 hp at the flywheel

The above assumes that the TBI is stock GM using 65#/hr injectors from the LO5 9C1. The brake specific fuel consumption (BSFC) is typical for a small block and I used 0.5 as that's a better consumption value for rpms near peak power. Note that the above represents a limit imposed by the fuel delivery (injectors, & fuel pressure).

Now for the limit imposed by airflow. The stock TBI, as I understand, is flow limited to 500 cfm. And I also know that a 270 fwhp LT1 needs 220 g/sec airflow peak to make the 270 fwhp.

220g/sec /(1200 g/m^3) = 0.183 m^3 per sec

1.2 kg/(meter^3) is density for air at, or close to STP.

0.183 m^3/sec * (foot/.3048 m)^3 = 6.474 ft^3/sec

6.474 cubic-feet/sec * 60 sec/min = 388 cfm

So 270 fwhp is to 388 cfm (per LT1 data) as
X fwhp is to 500 cfm; solve for X:

X = (270/388)*500 = 347 fwhp.

So the airflow limit of a 500 cfm TBI could, in theory, reach 347 hp... but in practice you'll never get there because the 500 cfm assumes a no air flow loss. So I'd expect more like 450 cfm as best (massive air cleaner, largest filter you can use, and cold air feeds) so the max power based on airflow is more like 0.90*347 = 313 fwhp.

So the stock TBI isn't really challenged by airflow, but it is by fuel. Larger TBI injectors can help solve that, but you will need to alter the ECM tables. The band-aid shortcut is to keep the stock injectors and stock ECM, and raise the fuel pressure, either manually at the track or using the vacuum-compensated FPR.

Oh btw, I never mentioned the camshaft in the above, because I was only looking at the ceiling imposed by either the airflow in the TBI itself, or the fuel delivery system also by itself. The rest of the engine (cam, intake, exhaust, heads, valves etc) could also impose their own limits on power, but I've assumed everyone here knows that. FYI. - Ken

 

And a 390cfm carbed Nascar motor can't reach 600hp... Just cannot be done.

EDIT: Just realized that your math calculated 313hp max. That's EXACTLY the high hp limit I got on the engine dyno with the small TBI/350cid!!! Like, exactly! Maybe that's the actual limit? I'm gonna shoot for 350 next, then 400 with the Hot Cam. We shall see.

[This message has been edited by FastBroker (edited July 20, 2001).]

 

for whatever it is worth, I am going to see what my quarter times are with my G-tech/stopwatch with the stock TBI + 65# injectors. I have another edelbrock TBI manifold which is bored to 2" and a 454 TB which I am installing in a few weeks. I will check the stopwatch/g-tech after the install just to see and let you guys know. I am sure its not a great comparason cause I am running the 350 cop which is not optimized for either set up but I just wanted to see. After I do the swap, I am gonna have a custom chip burned either with ed wright or dave johnson in denver but i don't have enough time or money to optimize the chip for both induction set ups.
I am also curious to see if the larger TB leans out the engine cause the cop chip is running somewhat rich at almost all rpm levels with the stock TB and I have never been able to optimize mixture with fuel pressure alone. Both ED and Dave felt that the bigger TB would help at 5,000 + rpm but are not sure if it is cost effective. we shall see...........bob

------------------
91 camaro RS convert,GM crate 350 with LT1 cam,edelbrock 6085 heads,9.5:1 comp, edelbrock TBI intake, 65# injectors, GM cop chip,dual fan conversion,
ultimate TBI mods,TBI spacer,SLP 1 5/8 headers,
3"cat back,Flowmaster,
T-5, centerforce 2 clutch, 3.42 torsen posi,alston SFC's,Global West LCA relocation brackets, edelbrock STB

 

yea i am one of the people who bought the new holley tbi with gm injectors atleast thats what i am told and i have some pics of it here http://firbirdgta.tripod.com/cars/id9.html

 

i am still using a stock unit. i have modded the top of it, but is still has the stock bore. i run 350 injectors in it and an adjustable regulator.

lata
tim



------------------
91 Camaro RS-LO3,Auto.
14.209@95.46mph
Best 60' 1.917
Check Out The East Coast F-Body Nationals Home Page
www.geocities.com/njspeeder

My MAFB.ORG Home Page
www.mycar.net/mafb/registry/detail.cfm?id=299

DSI Racing Home Page
www.geocities.com/foff667

 

Way to show off the math skillz KD! Thats impressive, and the numbers make sense.

Something i also just started wondering, could the 500 CFM rating be without the injectors in place? They are so detrimental to airflow sitting where they are, just a thought.

------------------
88 Camaro (not an RS, or an IROC, justa camaro.)
305TBI/700R4/2.73
14" Open Element and Flowmaster 80 seires

Next up: headers and gears

 

I bet it's rated with the injectors IN PLACE... and from what I understand, a number of non-GM people have flow tested the TBIs on their own flow benches, and the only smart way to do that is with the injectors attached.

David Vizard, in his Chevy cylinder head porting book says that at low lift, the greatest thing impeding airflow in a cylinder head is the valves. But at high lift, it's less of the valves and more the valve seat & port impeding the flow. So my guess is that the GM fuel system engineers knew that, and that they placed the injectors high up enough so that they wouldn't impede the flow that much. And really, at part throttle, it's the throttle plate that's the major flow stopper (deliberately ), but at WOT the throttle plates are almost invisible to the flow.

I bet the engineers placed the injectors high enough up so that they wouldn't cause that much reduction in flow at WOT, while still allowing the injectors to spray the fuel into the high velocity venturi for good fuel-air mixing. - Ken

 

I have other points to add to the topic.

The calculations used show the best choice of parts to be used... power over what the calculations show can be made with the given injectors or TBI unit but in theory they will be a restriction beyond that point and more power will be made with a larger injector or air meter. As Fast Broker was illuding to, this is how Nascar makes the big numbers with restrictor plates... but get rid of the plates and they make much more power.

Another point of note is that 2bbl TBI units are flowed at 3", not the 1.5" that 4bbl carbs and 4bbl TBI units are measured at. This means that 450cfm from a 2bbl TBI is in fact much less airflow than a 450 cfm carb.




------------------
1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter, 360ci, 9.8:1 cr,
AFR 195 Heads, Weiand #7525 intake, Lunati roller 219/227, .479/.480, 112 LSA
GM big block 2bbl TBI on truck 7747 computer

 

Dan, based on the calculations above showning the limitation of 260 HP with 65# injectors, are you using 80 # injectors or did you just crank up the fuel pressure? Thanks.........bob

------------------
91 camaro RS convert,GM crate 350 with LT1 cam,edelbrock 6085 heads,9.5:1 comp, edelbrock TBI intake, 65# injectors, GM cop chip,dual fan conversion,
ultimate TBI mods,TBI spacer,SLP 1 5/8 headers,
3"cat back,Flowmaster,
T-5, centerforce 2 clutch, 3.42 torsen posi,alston SFC's,Global West LCA relocation brackets, edelbrock STB

 

I had to run my 55pph injectors (rated at 11psi) at 20psi to get my 313hp, FYI... Around 74pph that way, I guess... (x)4 = 296hp... Close enough.

Ever see/hold a Nascar restrictor plate in person? WOW, talking about small holes. Spent some time with the DEI boys this weekend at Laconia... Fun stuff.

 

wheres a good site to buy the 454 tbi, or 670cfm holly tbi thanx

 

Firbird,

I am VERY sure that the injectors are still the same Holley-made pieces BUT they redesigned the injector cap/connector as the injector pins would not "center" themselves in the older Holley design connectors, thus causing injector misfire/non-operation. A simple disassembly of the injector pod top and injector removal will let you know. VERY different installations of the actual injectors.

EDIT: Ie, after checking your pix more closely, I am ABSOLUTELY POSITIVE that you have the same-old Holley-made injectors with the Holley stud/plate injector hold-down method... Sorry... Holley uses a very different injector pod/injector retention system than that of the GM/Rochester TBI system. Needing a new connector was half of Holley's problem, though... Just don't use too high a pressure on those injectors long-term. They don't like it and wear out/stick fast. And make sure your injector Weatherpak connectors (or solder connections if you did that, no crimps as they WILL fail eventually!) are in REAL GOOD shape!!!



[This message has been edited by FastBroker (edited July 23, 2001).]

 

where to get the 670 cfm tbi??

 

Not that I doubt your math abilities, kdrol, but I am wondering where your equations are coming from. Namely, the equation that relates injector size to hp. Where did this come from, and how do we know that it accurately describes a relationship between fuel delivery and horsepower? If this equation were correct, then the supercharger and NOS companies have got us all severely duped! This would mean that the most a 350 TPI with stock (22 lb) injectors could make would be 391 hp with a BSFC of .5. Correct me if I am wrong, but aren't there cars making more than that on the stock injectors? How can that be explained? Perhaps the fault is in the BSFC number. How is this calculated? I am not doubting your equations, I just need a little more explanation to believe that they are accurately describing the relationship between fuel and hp.

Secondly, your calcualtion of the airflow required to provide 270 fwhp to an LT1 assumes that the hp is not limited in the LT1's case to the amount of fuel being provided. Granted, if the first equation accurately describes the relationship between fuel and hp, then the LT1 should be capable of 391 (?) hp and thus fuel would not be the limiting factor. But even assuming that, what if the cam/heads, exhaust, etc. are the limiting factor in the LT1 and not the airflow? (I don't know if it is or not). This would mean that the LT1 is capable of making more power from 220 g/sec. And if this is the case, then the stock TBI could be capable of more hp than calculated. My point after this convoluted mess is that I think we need a general equation that relates CFM to hp rather than using the example of the LT1 so that we can more accurately approximate the max. hp of our cars. Reason: we aren't sure (or at least I'm not sure) what the limiting factor of the LT1 is.

Does this make any sense? I hope I don't seem like I am splitting hairs or being a smart-aleck. I would just feel more comfortable (1) knowing where the hp to fuel equation comes from (as well as the BSFC number) and (2) having an equation that relates cfm to hp that isn't based on an example in which we do not know the limiting factor.

[This message has been edited by JRoy91RS (edited July 23, 2001).]

 

I though that all throttle bodies were flowed at 1.5in/Hg due to the fact that they don't have venturies. They just have throttle bores. There is no velocity increase through the bores like there is in a venturi of a carburetor. There's really no need for it. The air doesn't have to suck fuel out of a bowl, so there's no need for a venturi to build velocity.

If what you're saying is true, then a 450cfm@3in/Hg throttle body will only flow 318cfm@1.5in/Hg. That's very little. I don't know a 350 made that can flow that little. Even a very mild one with a 85%VE will want 387cfm@1.5in/HG @4500rpm. Even more if the rpm goes up. Even a little 305 needs 337cfm@1.5in/Hg @4500rpm.

I'm not trying to say that your wrong. It's just a new shocking discovery to me. I guess now I know that a 4v carb is the way to go for big power. Hell, even that 670cfm Holley TB would only flow 473.76cfm@1.5in/Hg. That's hardly worth the money. A 750 dbl. pumper is only $300, and you don't gotta **** with the ECM.

Thanks for the info. I learned something new today.
AJ

[This message has been edited by AJ_92RS (edited July 23, 2001).]

 

so, anybody interested in help funding my larger tbi yet. LOL

 

Are you gonna have it flow 950+cfm? That's what it'll take to match 670cfm@1.5in/Hg. Now I see why companies make 1000cfm throttle bodies for TPI.

If you plan on getting that much flow, then I'm game. Just give me about another month. I gotta workman's comp settlement of about $250K coming soon. That should hold me over for 5yrs or so.

TTFN
AJ

 

AJ_92RS:
Yep, The info on the 2bbls being rated at 3" came from a book I have kicking around somewhere. It says that it carried over from 2bbl carbs. I also heard it being kicked around on the board here. A while ago I e-mailed holley and they confirmed it. Here is the reply: "We flow the 4 barrel units at 1 1/2 inches of vacuum. 2 barrels at 3 inches of vacuum. We flow everything with air and fuel. Not just air.
There is a difference."

JRoy91RS
The cars making more power with stock injectors get the extra fuel by raising fuel pressure. Many NOS systems add both NOS and fuel. The equations for fuel requirements are floating all over the net. BSFC is the biggest variable but gasoline engines tend to operate within a given window of fuel consumption. These equations are ok for tossing around theory but are best used for trying to make an edjucated choice prior to buying parts.

Regarding airflow, optimum airflow is just that... it should not be construed as a limiting factor. More power can be made with less than optimum airflow and motors are generally no where near as sensitive to this as they are to too little fuel. Too little airflow will hurt power but its not like you suddenly run into a wall... ie: you change your cam and with the correct TBI unit you would add 20 hp up top but you only get 15 because you are airflow restricted.

In the end these calculations are only good for estimates and generalizations. Specific combos must be tested to see how they respond.

1989camarorsrs
The holley 670 is available from any holley distributor for around $300. Used GM 454 TBI units utilize a superior injector and can be had for that price or cheaper from junk yards or e-bay. Other than the injectors they are a similar design.

Fastbroker:
Never seen a restricor plate in person but have seen them on TV being held in a guys hand... Not a huge Nascar fan.

rsilver:
My TBI unit is from a '87 454 truck. It features 90# injectors from the factory so I should be ok at least at this altitude the afr heads seem to be very efficant BSFC wise so that also helps...(I think it has lots to do with combustion chamber shape) Still havent found time to fix my TBI problems though so it remains untested.

 

I'm not so much a Nascar fan, either... Just a Nascar Engine Fan!!! Plus, they really are fun to drive around a bit... Those are some good words of wisdom. you gotta run the stuff to see if it works!!! Equations are great, but not always right.

EDIT: I've gotten 400hp+ out of several 355 SBC's pretty easily with a Holley 390cfm 4bbl (rules suck!)... Vacuum signal, smackuum shignal. who cares. Still a good motor and better than what we got stock... The small carb helps throttle response A LOT with a big cam, that is for sure. Actually helps to make it quite streetable. Yeah, not a quarter-miler, though.



[This message has been edited by FastBroker (edited July 24, 2001).]

 

If you did, in fact, get 400+ dynoed horses from less than 400 cfm, this would provide a counterexample to kdrolt's equation which he derived based on info from the LT1. This COULD be very good news for those of us wanting to stick with the stock TBI. I say "COULD" because I don't think that CFM is an independent variable when determining horsepower. Neither is fuel delivery. I'm not a physicist, but this would explain why the above equations don't work. They oversimplify the relationship between fuel, air and horsepower.

 

Guys you see on TV get 500-600+ hp all day on the same 390cfm carb. I'm saying that they don't rev up so quickly, but in an oval track car where everyone has the same RULED setup, it doesn't matter. You need the HP/torque to win the race... ie, would NOT make good drag engines in that a 500hp'er with a 1000cfm carb would surely beat a 500hp'er with a 390cfm carb.

I have used 600-650cfm's on 502's with pretty good results,as well, for streeters.

 

Measured data on my car using Diacom. I know what the MAF data is in g/sec and I know how to convert that into cfm. I also know that my car makes approx 10-12 hp more than stock, and the timeslips are consistent with that, as well as with data from other data via Diacom/Autotap from other cars & owners.

[quote]<font face="Verdana, Arial" size="2"> Where did this come from, and how do we know that it accurately describes a relationship between fuel delivery and horsepower?[QUOTE]

I think I answered that in the above, but it would be fun (as an alternate calculation) to take the mass consumption of the fuel (or fuel delivered in #/hr) as a rate from the injectors, and calculate the energy available from the fuel, and then take 25% of that and assume that only the 25% goes into mechanical work, and that the rest is "lost" into heat. That would be a neat sanity check, and I haven't tried that yet. It's more math hoop-jumping, but it's all simple. I just need some data for gasoline.

BTW, the formula for power as a function of fuel flow and BFSC is probably a very accurate one PROVIDED you get the BSFC data right from an engine dyno. There are, however, enough dyno tests on the web (or in car magazines) that show rpm, torque, hp, and BSFC that my assumption of 0.5 is reasonable for a 350 near the rpm for peak power.

The only item that I did forget, in hindsight now that someone above mentioned it, is the VE (volumetric efficiency) at the rpm for max power. The VE is close to 1.0 at the rpm for peak torque, and it usually drops a bit as the rpm climbs. So the math I did could be regarded as optimistic because I implicitly used a VE of 1.0. I did, however, derate the useful cfm from the TBI from 500 to 450, so that assumption could cover things well enough.

[QUOTE] If this equation were correct, then the supercharger and NOS companies have got us all severely duped! This would mean that the most a 350 TPI with stock (22 lb) injectors could make would be 391 hp with a BSFC of .5.[QUOTE]

(8 injectors * 22 lb/hr)/(0.5 lb/(hr hp))

= 8*22/0.5 = 352 hp based on fuel delivery alone.

What I had omitted from the math before, and as someone just reminded me, is the VE (volumetric efficiency). The fuel supplied in a TPI is enough to make 352 hp IF a BSFC is 0.5, and IF there is enough air to go with it. But if the VE is only 85% at the rpm for peak power, then the max hp will be 85% of 352, or 299 hp.

So if you want to see what the fuel limit on power, by itself, use

hp = (#injectors) * (lb_fuel/hr) /BSFC

If you want to see what the actual output of the engine would be, including fuel and including the volumetric efficiency, then use

hp = (#injectors) * (lb_fuel/hr) * VE/BSFC

and you can use VE = 0.85 to be safe. The VE is close to 1.0 at an rpm near the torque peak, but the specific intake and exhaust alter exactly where peak VE occurs.

You would still need to sanity check whether the airflow is enough, and for that I needed the LT1 data that maps cfm airflow into fwhp.
I could have done it with data from another car (TPI, TBI) but I didn't have it handy.

I think someone (Dan? I can't see the post as I write this) answered: if you use a blower, the mass flow rate into the engine is much higher than stock. The way to include that in the math is to let the VE be a number greater than 1.0.

Example: you have a blower on your 350. You run 5 psi boost. Well, atmospheric pressure is 14.7 psi, so running a boost of 5 psi on top of the atmosphere gives you a cylinder filling of (1 + 5/14.7), or 1.34 times normal, than what you would normally get naturally-aspirated. So the VE would be 1.34, in theory. Of course the blower heats the air so the density drops (no intercooler) so the effective VE will be lower than 1.34, and maybe only 1.2 to 1.3 for example.

So the output would be 1.3 times the normal output:

hp = 8*22*1.3/.5 = 457 hp

btw I cheated a little in the above because I let the VE go from 0.85 to 1.3 to account for the blower, but I would have to add the extra fuel to let that power come out. So now I'll work the math backwards to see by how much extra fuel I'd need:

457 hp = 8*[X]/.5

and now solve for the unknown X.

X = 457*0.5/8 = 28.6 lb/hr

So my injectors have to be able to provide 28.6 lb/hr in order to achieve 457 hp. So I either need Buick 30# injectors, or I need to bump the fuel pressure. Actually, I'd need to bump the fuel pressure up anyway to let the injectors overcome the higher intake air pressure from the blower.

And the NO2 setup always includes an extra set of fuel nozzles to add fuel along with the NO2. There's cookbook math for that too.

[quote]<font face="Verdana, Arial" size="2"> Perhaps the fault is in the BSFC number. How is this calculated?[QUOTE]

It's measured on an engine dyno. The torque is measured at each rpm, then hp is calculated from hp=torque*rpm/5252 (assuming the correct units are used), and then the flow rate of fuel (measured with an inline meter on the fuel line) is used together with the hp for that specific rpm. Take the fuel flow rate and divide by the power rate (aka hp) and you get BSFC.

And yes, my choice of 0.5 is an assumption (as I stated) but it's actually conservative for a 350, and very very conservative for a 305.


...

[QUOTE] Secondly, your calcualtion of the airflow required to provide 270 fwhp to an LT1 assumes that the hp is not limited in the LT1's case to the amount of fuel being provided.[QUOTE]

The 24 # injectors are on LT1 are good for approx 400 fwhp when the duty cycle for pulsing the injector is close to 100% of the time -- i.e. full open. So 260-270 hp is certainly not limited in fuel delivery by the stock injectors.

I could have used "calibration" data for airflow (in g/sec, or in cfm) from a TPI engine, and by knowing the timeslips and car weight (to get hp). It would be fun for someone to repeat the entire math exercise for a modded TPI car that has Diacom or Autotap data collection. I don't know if there is a way to get airflow data on a TBI because that system is speed-density and has no MAF..... ahhh but if you added a anemometer and a data logger you could.

[B]

Correct, and agreed.


[quote]<font face="Verdana, Arial" size="2">[B] But even assuming that, what if the cam/heads, exhaust, etc. are the limiting factor in the LT1 and not the airflow? (I don't know if it is or not). This would mean that the LT1 is capable of making more power from 220 g/sec.[QUOTE][B]

That's a valid point, but at 5000 rpm the LT1 head (same as L31 Vortec as far as flow is concerned) is not taxed... and many of the engine buildups using L31 heads in the car magazine bear this out. And there's no question that the LT1 Bcar cam (stock in my car) is very mild so the cam also factors in.

You make a good point. It would be neat to see how this all stacks up on a given car after a sequence of mods. Does the relationship between airflow and output power change, assuming the air-fuel is held close to constant? I believe so, but I don't have the data in hand to prove that.



Perhaps, but really don't think so.

The TBI unit *is* limited in airflow such that you won't see more than around 350 hp in theory, and probably more like 300 hp in practice, on a 350. With NO2 you can get more, but that's only because the extra oxygen comes from the high pressure fogger and not airflow thru the TBI. And the NO2 system supplies fuel from a different source than the TBI injectors.



Good comment.



It does make sense, and you're right -- we don't know (or at least *I* don't absolutely know) what the limiting factor is on a TBI. But I do believe that the cfm to power conversion for the LT1 is a reasonable one to use for any well tuned modern engine, and I do believe the math mess that says a stock TBI is much more fuel limited than it is in airflow. The math may not be perfect, but it's close enough.

Sorry for the length. - Ken

 

350hp+ on a 350...

 

Then why did you (Fastbroker) previously write on 20 July:

"...Just realized that your math calculated 313hp max. That's EXACTLY the high hp limit I got on the engine dyno with the small TBI/350cid!!! Like, exactly! Maybe that's the actual limit? I'm gonna shoot for 350 next, then 400 with the Hot Cam. We shall see."

You say you got 313 hp on an engine dyno w/small TBI on a 350. I believe it.

Were you using the exhaust planned for the vehicle, or the shop low restriction exhaust? Did you test with the same headers (if any)? Was the in-vehicle air cleaner installed on the engine during the dyno run(s)? Was the engine turning it's own water pump, or was the coolant water being pumped externally?

If the engine dyno tests were run without these items (i.e. measuring gross hp, the way they did in the 1960s), then the actual useful in-vehicle hp at the flywheel will be less.

You also said you were going to shoot for 350 hp and then (later) 400 hp with the LT4 Hot cam.... have you already done those tests?

Have you already reached 350+ hp, and did you do that test in a gross or net engine dyno configuration? Or are you wishing that 350+ hp is the limit? And I am talking about a small TBI (for sbc 305 & 350 cid) on a 350 engine.

On the other item you posted, re 390 cfm carbs. 390 cfm from a carb, by my math, is limited to around

390 cfm * 270 fwhp /(388 cfm) = 271 fwhp

... and maybe 290-300 on an engine stand in a gross hp set up (no fan, no aircleaner, shop exhaust, no water pump, no alternator). For a 390 cfm carb to reach 600 hp, it's not going to be through a carb that really pulls 390 cfm. The airflow would have to be almost double. And even if you don't accept that 388 cfm equates to 270 fwhp, or 1.43 cfm per hp, the factor isn't that far off.

390 cfm is, I think, the smallest 4v carb that someone can buy for a street motor. A race car would more likley use a 750 or 850 cfm carb at the bare minimum. IMO.

 

In re the preceding, here's one example from NASCAR:

http://www.mcdonalds.com/countries/u...us/taurus.html

(I know it's a Ford, but it's the first one I looked at)

358 cid v8, 700 hp, (380 hp w/restrictor plate)

carb = 850 cfm Holley

850 cfm /700 hp = 1.21 cfm/hp
(we also don't know if it's exactly 700 hp).

I prev used a conversion of 1.43 cfm/hp. As I said, the ratio of cfm/hp is fairly constant, and at 12:1 air:fuel ratio, cfm is a good number to use to estimate hp. FWIW and FYI. - Ken

Edit - see:

http://members.nbci.com/HWilkinson/EB.htm

He (the author) writes:

"There is a great deal of misunderstanding of engines out there, not to mention considerable misrepresentation of engine power output. All internal combustion engines produce horsepower in direct proportion to the amount of air/fuel mixture they are passing through at any given time. This rule applies to ALL internal combustion engines..... 4 cycle, 2 cycle, naturally aspirated, or supercharged. A standard engineering figure for this ratio is 1.62 CFM (cubic feet per minute) per horsepower (.6 hp per CFM) This applies pretty well to engines in the compression ratio range of 8x1 to 9x1."

Note that the author of the above didn't account for the parasitic power needed to drive the water pump, the cooling fan(s), etc, so his figure of 1.67 cfm/hp is understandably higher than mine. His is a gross estimator for gross hp at the flywheel, or in his case at the propellor shaft (airplane application). Mine is net because my was collected from in-car data. The web site is worth looking at. FYI.



[This message has been edited by kdrolt (edited July 24, 2001).]

[This message has been edited by kdrolt (edited July 24, 2001).]

 

What you don't understand (or aren't sunig "common sense") is that the cfm rating of a carb takes place under certain bench conditions/vacuum levels. Engines can operate at high vac levels carbs can operate at very high "vac" levels, although not ideal situations, ie Nascar restrictor plate racing effect the engine vacuum but not the vac seen by the carb, as the RPlate plate is below it.

I'll try to get to a 390cfm-ruled engine website and post what I can find.

Anyone care to guess what the cfm rating of a Nascar restrictor plate is or even know what the diameter of the holes is???

EDIT: If I said I was goona "shoot" for something, how could I have done it already. Testing pending the stock market...

Also, book smarts, "generic" engineering terms, basic reasoning, rules-of-thumb, etc, don't hold true in real life A LOT OF THE TIME, especially in heavily modded engines.

313hp test done with 1-3/4 headers (too big!), stock air cleaner, entire serpentine belt package hooked-up, (no Alt conn/AC conn) stock OEM pickup rev-rot H2O pump, Flex-a-lite serpentine flex fan (waaaaaaay too much) so I probably was at more like 330hp without all that crap, especially the fan. You should hear that mother at 5grand... Oh, Edelbrock 3" Elite air cleaner, too. Compe has gotten 331hp on the engine dyno with close to my setup, I believe, with no parasites...


[This message has been edited by FastBroker (edited July 24, 2001).]

[This message has been edited by FastBroker (edited July 24, 2001).]

 

http://www.rpmeng.com/rpmpic.htm


Hope the link works... 525hp, 390cfm Holley carb...

EDIT: It works. As I said above, RULES racing sucks, but you can still scoot along pretty well!!!



[This message has been edited by FastBroker (edited July 24, 2001).]

 

Originally posted by FastBroker:
Here's what I do know. If you put a perfect vacuum within the intake, and 1 atm on the outside of the carb/TBI, and then measure the flow rate of the test article (carb or TBI), you will get the maximum flow (max cfm) that the test article can achieve. It can't get any higher than that, because there is no greater pressure difference that can be applied with airflow.

In a race car, or street car for that matter, you NEVER get the perfect pressure difference that I described in the above paragraph. It's always less than perfect, partly due to losses in the air cleaner and filter, and partly due to the finite draw that the engine can make in the intake plenum. So under those conditions, the flow of the carb or TBI will be less that in the perfect test from above.

So the question is, in a street car, what is the pressure differential measured above and below, at WOT? Then repeat the same question for the race car, also at WOT. The repeat the question for a race car ALMOST at WOT. If the pressure differential is much greater than the 1.5" and 3" quoted (per Superflows website), then that would completely explain why a 390 cfm carb can flow more than 390 cfm.

The problem is that I don't know enough of the actual pressure difference data, and readers and posters often toss around inches of water and inches of mercury without knowing what those terms mean. I know enough about them that I always try to be careful in quoting them.


Great. Thx.


I'll guess.

Based on the McDonald's NASCAR Ford info I supplied, they claim 380 hp out with the restrictor. Using 1.43 cfm/hp, that works out to 380*1.43 = 543 cfm. If you use 1.2 cfm/hp (as obtained from the same McD NASCAR web site), you get 380*1.2 = 456 cfm. I figure the people writing the web page aren't giving the whole story... so I'd say that it was a 550 cfm, and maybe as high as 600cfm.

A stock sbc TBI has a 1.68" diam bore, so that's pi*(1.68^2)/4 = 2.217 sq-in... and times two for two bores: 4.43 sq-in. It's supposedly rated at 500 cfm. The NASCAR plate has four bores and is (my guess) rated at 550 cfm, so (550/500)*4.43 = 4.88 sq-in.

Divide by 4 bores: 1.22 sq-in.

Diameter per bore (assumed all equal) = 1.25" diam per bore. I don't know if the carb they use has two small primaries and two small secondaries (like a street car), so if they did use one like that, I would expect the bores to be proportionally sized (two big, and two small).


Fine... but you said "350+ hp" right on the heels of saying "313 hp" which suggests that you had a measured answer; you don't actually know (yet) and that's why I was asking.

I don't agree with that. What you say is only true if one don't completely understand what's going on, from the engineering side especially on a heavily modded engine. All of what happens in any engine can all be explained by engineering, physics, and math. All of it. And the best people doing the most heavily modified engines would be lost if it weren't for the slick engineering and on-board diagnostics that they collect during a race (or a dyno pull).

The fan will flatten and draw little at high rpms, as designed. In a car, the fwd movement would provide enough airflow. So the fan probably wasn't worth that much power, unlike a fixed blade fan. The too-large headers probably helped the peak power, but you took a hit in torque.

Thx and 330 is close enough to 331.

If you had it on an engine dyno then you must also have gotten the fuel consumption rates, and so you can get BSFC vs rpm. If you had a hotwire installed, then you could also get a good approx of the airflow rate. The airflow rate as compared to theory will give you VE vs rpm, and the BFSC and VE are all you need to tighten the math. I bet the correct BSFC and an 85% VE would make the ballpark estimate of 313 come in around 330.

Btw the math ALWAYS works, always. If the math doesn't add up, it's because the assumptions don't fit the problem, or the wrong math is being used, or there is an error somewhere. The challenge is always in finding out why. - Ken

[This message has been edited by kdrolt (edited July 24, 2001).]

[This message has been edited by kdrolt (edited July 24, 2001).]

[This message has been edited by kdrolt (edited July 24, 2001).]

 

wow my head hurts after reading that

 

My head hurts too! WTF? Well, I am gonna just do it...bob

 

my opinion.

with fuel injection. there is no reason to leave a restriction in airflow if you dont have to. which we dont because we can tune the fuel to the engine, and let the engine get however much air it needs.

screw vacuum.

 

That fan uses 15-18hp at 5500rpm. I have verified this in the past and Flex-a-lite has agreed. If you heard it, trust me, you would understand, like a mini-turbine engine. Even the dyno operator commented on how loud it was. He thought it was gonna come off cause I use a 3" spacer to get it to fit with my truck serpentine belt package. It is the BIG bladed one, not the skinny bladed variety. Yeah, you can see it flatten, but not by a ton, and surely not all the way... That fan costs me more than 1mpg at 2400rpm on the highway in my Jeep, too, as measured by more than 10 tanks of gas. 5500rpm is a lot of tip/wind speed... Fan is actually too big for my Jeep now by I have been using is since my old four-wheeling days when low-sped cooling was a must.

I am done now. 390cfm and 500-600hp done every day. I posted a link that shows a mellow 525hp/390cfm purchasable motor for all to see. Good/private/team engine builders get 550-600hp... Book smarts are great, and I have lots, but real world is a little different. We are all entitled to our own opinions and real-world experiences. If you can make the motor, put it into a car/truck and DRIVE it. You can't drive OR DYNO TEST a book. Not yet, anyhow.

I'll stand by my 350 and 400hp goals and eventually will back them up with chassis/engine dyno testing. Talk is good, but dyno is best. I am also putting a 390cfm on a client's Son's brand new 330hp/350cid Vortec-headed crate motor this weekend. It will limit the ramp-up of the motor sum, which the parent expressed concern about to me, along with the benign HEI curve I will put in it for him. Kids first car and only 18, don't want to have him expire too soon, like stock options sometimes. Not that anyone cares but I started with the 390cfm carbs on Chevys in 1990 when I bought one for the original inline 258cid 6-cyl that came in my Jeep. Clifford Intake with 390cfm Holley carb, cam, head work and some headers. Went to Chevy V8 power in less than one year and got into ASA and other 390cfm ruled motors after that. A 390cfm carb takes about $250 to work well on a V8 after the initial $270 purchase, but that's cool.

If you think a 390cfm cannot make 500-600hp ON PAPER but it ACTUALLY CAN/DOES IN REAL LIFE, what are the equations that allow it to do so, and for this to happen if it cannot on paper??? Me, I don't really care but others may and you should satisfy your math equations. I could break-out my College books and probably get a half-**** answer but fortunately for me, I have MUCH better things to do today and will let someone do the work for me.

[This message has been edited by FastBroker (edited July 25, 2001).]

 

Originally posted by FastBroker:
I stand corrected.

I think you missed something important in the preceding discussion.

If the engine is making 500-600 hp, as measured on a dyno, then it's not flowing only 390 cfm. The carb may be advertised as a 390 cfm, especially for use in a street car with a limited pressure differential (or vacuum if you refer), but on the race motor it's NOT 390 cfm.

Those skilled with simple math can back out the actual cfm by knowing the power output measured on the dyno and working backwards through the math. Assuming that the air-fiel ratio is around 12:1, the dyno data will sensibly back out both the airflow and the fuel flow.

I already posted the math, and explained how/why a 390 cfm carb could flow MORE than 390 cfm (it requires a greater pressure differential, 1 atm up top and something closer to a perfect vacuum in the manifold).

The upshot is that if you (or anyone else) buys a 390 cfm carb, will it outflow 390 in street use?

On a 305? Or on a 350?

The answer is, it depends on the engine, the heads, the cam, the intake, the exhaust, and the air cleaner. On a street engine, it is not likely to outflow the mfg rated flow. On a race engine, it probably will.

My closure, in bringing this discussion back to the TBI question of "how much power can be made from the TBI" is that just because someone makes a lot of power on a race motor with a 390 cfm carb, with a race cam, race heads and exhaust, and otherwise set up for WOT high-rpm operation, doesn't mean that you will be able to run a 2 port stock TBI with 1.68" bores beyond the measured flow rating of 500 cfm, or my swag of 450 cfm with losses.

In a street engine, especially a mild one, the airflow will limit the output to around 313 fwhp. Beating 313 fwhp can probably be done using the stock sbc TBI unit, but it's not likely to be a fun engine to drive on the street. IMO. - Ken


[This message has been edited by kdrolt (edited July 25, 2001).]

 

Why don't we agree to disagree. We shall see what I can do...

 

You guys are saying the same thing.

 

i got a good idea as soon as i get my vortec heads and intake ill put my 355 in get it dynoed and c how much power the stock tbi will make adjusted fuel preesure and all

 

Do that but that doesn't mean that's ALL the power the TBI unit can make. Just can make with your combo. Have fun and good luck.

 

put a small block tbi on a 454, see what the drop is. how about that?

that will give you a comparison point to start playing with even more math.

or you could find a beefed engine and throw a tbi on it, knowing what it could make with the same bbl sized carb. and see what happens.

just some ideas to try.

either way. im sorry, math is not objective. nothing is. no matter how hard you try. there is always some play because a person is building the formula, and they are surely subjective. you will subconsiously try to make your formulas proove your original thoughts.

o, and though i think ive figured it out a bit. you guys seem to have fun figuring stuff out.

how about a 58mm tbi unit. what is it going to flow at 1.5 and @ 3?


[This message has been edited by snflupigus (edited July 26, 2001).]

 

Great point. Even horsepower measurements/calculations are based on one man's thoughts as to how much work 1 horse can do. He guestimated. Plus he rounded to whole numbers, and sometimes rounded to the nearest hundred. But it has become the "standard" that the world now uses. It does not account for any variables, which we know (at least in my world) always take place.