i'm trying to figure out what the upper limits of tbi are for bigger c.i./higher hp applications. i'm eventually going to replace my 305 with a bigger engine, but want to learn just how much airflow i can get out of a tbi before i start serious planning, as that appears to be the limiting factor.

which flows more air in stock configuration, the holley 670 or the 454 tbi?

in past posts, guys were talking about how the injectors on the 670 sucked and they were swapping the stock tbi injector pod onto the holley unit. has holley addressed the injector issue yet?

if you want to flow the absolute maximum amount of air with a tbi, what would you do? someone posted a link to a truck board post where a guy had bored and sleeved a 454 tbi to the size of a howitzer or something, but i can't find the link.

 

Stock = 400cfm
454 = 600cfm
Holley = 670cfm

for the ULTIMATE TB, look into the holley 900cfm 4bbl TBI.

 

holley switched over to a better injector made by delphi(?). Theyre alot better then the older ones that they used to use. Keep in mind that all those flow rates are at 3 inHg and not at 1.5inHg like the 4bbl carbs are rated at. The ratings at 1.5 inHg will be less.

 

Dewey, not trying to put you down or anything but I'm curious where you got your data on the 454 unit. The castings I've compared were almost identical between the holley and 454 and they both use the same 2" bore... there were even some rumors a while back about some sort of relationship between GM and holley with the TBI units. The only real difference I can think of between the two is the injector pod and I cant see why that would cause airflow problems as they are about the same size.

Why do you think the 454 unit would flow so much less? I've always assumed they both flow the same.

 

What are your upper HP limits? Just wondering, it'll probably help answer your questions if you want 300 hp, 400 hp or 500+ hp N/A.

 

turbo city claims their modified stock tbi flows 590 cfm.

 

[QUOTE]Originally posted by dimented24x7
[B]holley switched over to a better injector made by delphi(?).


Delphi has been making parts for Delco for years......... Good quality stuff....

I just thought I would through that in the mix

Peace

 

i want to stick with a 2 bbl tbi .... seems pretty complicated to modify a stock computer to control a 4bbl tbi, and if i was going to go with a 4bbl, i'd go to an accel dfi or something like it.

 

i know this sounds dumb, but i don't know what the term "inHg" means. i guess "in" means inches, but what does "hg" mean?

also, what would the cfm of a tbi, 454 tbi and holley 670 be if the flow rates were calculated at 1.5 inHg?

there's a formula for calculating how many cfm an engine of a specific displacement needs at specific rpms, but i'm betting that cfm requirement is calculated at 1.5 inHG. with that formula and the actual hg of the various tbi units, it's not difficult to calculate how many cubic inches it can support.

 

beast,

as i understand the theory, at the most basic level, cfm limits cubic inches/rpm and max hp is determined largely by fuel flow. the question with airflow has almost nothing to do with horsepower and almost everything to do with cubic inches/rpm.

i've wanted to build a budget street engine for a daily driver for years. my plan is to start with a remanufactured 400 sbc short block with 8.5:1 dish pistons, ported vortec heads milled 0.30 to bring actual compression up to 9:1 or so, cam somewhere in the neighborhood of .500 lift, 220 (@0.5) duration (maybe a little more lift and a little less duration), and a single plane carb intake (to cut off-idle torque a bit) with a traco tbi adapter. obviously, there'll be some chip tuning involved, too.

i think this combination should make well over 400 hp and, more importantly, between 450 and 500 lbs ft. torque, provided i can get enough air and fuel to it.

if money weren't an object, i'd go with a complete accell dfi setup .... but you're talking at least 3500.00 just for the parts, and that doesn't include the harness to run the smog equipment.

before i give up on tbi, though, i want to see just what it can do. i've gone back to the beginning of the tbi posts on here and read many of them, but it doesn't look like there's a clear consensus on just how how may cubic inches tbi can flow enough air to support and how much fuel it can flow. i mentioned that hogged out, sleeved 454 tbi the guy on the truck board was making earlier. if memory serves me correctly, he was using 58mm throttle blades on it. that is huge!

there have been periodic discussions on the board about a project hot rod did back in 1989 called "f notes". they took a new 305 tbi 5 speed rs camaro and got into the very low 14s with the stock tbi unit (with 350 injectors). they changed the heads and cam, but didn't even have headers and didn't do anything with fuel pressure changes. a lot of people on here were unimpressed, but, for what they did, i think it's pretty amazing. applying the much better heads available today and 14 years of advances in cam technology, as well as a more free-flowing exhaust and fine tuning tricks like vafpr, etc. should lead to significantly more than they got.

they left a lot of information out of the article (cam specs, chip specs, secret tbi adapter, etc., as traco engineering, the company that did the work, was going to sell them and didn't want to give away the secrets. they've since gone out of business, and it's been tough getting info.

i was intrigued by a few things they did that seemed to make big differences. the first was the intake. they put the engine on a dyno and tested the performer tbi and the performer carb intake. they found the carb intake with an adapter made much more power. their best results were achieved with a custom tbi adapter they manufactured themselves. i was especially interested in it as their adapter is only 1/2" thick. i have an early trans am cowl induction system on my firebird and hood clearance is an issue.

the other thing was the cam. it made a huge difference and the duration and overlap were critical. actually, looking at their results, i'd run a little more duration. they made so much off-idle torque that it wouldn't hook up. need to cut that a bit.

i located the former owner of traco the other day and called him. he's a great guy! he said he has an adapter at his vacation home in north carolina and is going to sell it to me. he also gave me the name of the guy at engle cams who helped him develop the cam, so i'm hot on the trail of it.

one thing he said that interested me was that chevy gave them the car to see if the project would generate interest in performance tbi systems. he said they only had 4 calls in the two years following the article's being published!

when you think about it, it made sense at the time. if i could afford a new camaro or firebird and was really interested in performance, i'd find a thousand or two more to get a hotter setup, especially when you could build that into the loan and only raise your car payment 20 bucks a month or so. who wants to buy a new car and void the warranty by swapping heads, cam, etc.?

i don't think that lack of interest would be the same today. there are a lot of tbi camaros and firebirds out there used today and this board proves there are quite a few people interested in making them go faster.

anyway, to make a very long story short, as i focus on phase 1 of my project (squeezing as much as i can out of the 305), i want to begin planning pahse 2 (low buck/high power 400) and need to have a clear idea of just how much i can get out of a 2 bbl tbi.

 

Well, I won't start an arguement on the air flow for the street 400, but IMO the big bore 2 barrel, should do the job if money is a serious issue with the cam you describe and somewhat stock heads or cheap aftermarket.

On the 305 I can all but gaurantee that you can run low 14s or high 13s on the stock TBI with stock inj and stock fuel pressure (check my sig.). I've been running those times with little chip tuning and the stock air cleaner housing and the early (82-84) style cowl induction. It ran similar times with an open element. I haven't changed the upper fuel load vs rpm tables much (if any) at all. Just some timing and low rpm fuel.

I agree there is not clear answer on how much HP can be made with TBI (I wish someone would break new ground into this), but I'm going say I make ~230+ hp with stock inj (40pph?) with my 96.28 mph and 3500-3550+ race weight. So doubling that to 85-90 pph inj should flow fuel to 450+ hp IMO. Maybe I'm wrong with those figures and someone will help you out.

 

i have the 92-84 style cowl induction also. the previous owner did away with the solenoid and hooked it up to a switch ... how boring.

i have a friend with an 81 z-28 with functional cowl induction. it's so cool to ride in the car and watch the flaps open and close with the throttle ... one of those things that just adds tons of character. i'm curious to see what the differences are at the track with the cowl open and closed.

i'm in the process of switching to a new computer and can't currently access my files and links, so i can't get to the cubic inch / rpm / cfm formula. the problem with applying that formula to tbi is not knowing how much air a tbi flows at 1.5 inHg. surely someone on the board has put their tbi unit on a flow bench!

i just hate to jump into this without a clear idea. it's so easy to calculate the size of a carb and the jetting necessary for any combination i might come up with, but nearly impossible to do so for tbi because no one seems to know the airflow at 1.5 inHg and the actual fuel flow of different sized injectors at higher fuel pressures.

on a side note .... at some point, you'll hit the wall with tbi and want to switch to something else. dfi is incredibly expensive. a tpi system capable of handling that much horsepower is just as expensive. the stealth ram looks awesome and is inexpensive, but with no egr provision, there's no way to make it street legal. it's starting to look like a tpis mini ram would be the best way to go.

 

if you are really looking at hitting the "wall" with a 2bbl TBI, you should really look into the holley TBI system, it is about $1400 (alot less than a DFI system) and comes with a command 950 computer (the same one they put on the $2500 Stealthram) holley says it is good to 550 HP.

 

Yeah, I think the pph/hp formula is a little off. If I remember right, Jon made his 102 mph run on his 330 hp 350 H.O. with 65pph injectors a t 12 psi. You are making awesome traps with the stock injectors. So I really don't think fuel delivery is the issue. I think air flow is where the 2bbl tbi is restricted. But who knows....the 502 ram jet makes 500hp with the 48mm tb, so there may be some hope.
As far as breaking ground, I plan on doing so. My 383 should be worth 400+hp. I'm going to start off with my holley 670 and 85pph injectors, tune, tune, and tune, and see where it gets me. Hopefully I have her running within the next couple of weeks. My darn machine shop keeps pushing back the eta of the engine

 

i feel that one of the main keys to making power with teh tbi will be to get as much plenum volume as possible. Since there a re only two barrels you cant really go too much further with the cfm so optimizing the plenum volume and resonance will be the way to go. One fo the problems with having the stock tbi with the small intake is the fact that there is very little plenum volume to buffer out the pulses from each of the cyls. filling with air. IMHO, if you can get a large plenum under the tbi, youll see that teh ammount of power you can make will increase substantially.

 

how do you get that additional plenum volume? especially when you have hood clearance problems and can't go to a high-rise intake?

single plane intake?

 

thats the main problem with that is you have to modify/replace teh stock hood if you want to go to a high rise intake or a good single plane. Using the standard sized single plane may help but not as much as a high rise intake or a good single plane.

 

yeah, i know. i really don't like the looks of the aftermarket hoods available for my firebird. besides, i have the factory cold air setup from 82-84 trans ams on the car. don't want to lose that.

wish i could find the bandit 2 trans am shaker hood scoop. it actually looked pretty good on a third gen and it would have to be the most effective cold air intake you could come up with.

i'm leaning towards a single plane intake, anyway. the old traco engineering buildup i'm using as a template for my car had one problem: too much torque. it fried the hell out of the tires.

i plan on using 1 3/4" headers and a single pane intake to cut the off-idle torque a bit. will probably go with a little more duration on the camshaft to help with that, too (once i find out what their camspecs were). ha ha ha

i found the former owner of traco, who is selling me one of their adapters. he said they designed it because they didn't like the way any of the adapters available at the time flowed. also, it's only 3/4" thick, which should help with hood clearance.

 

rumor i heard was. gm contracted holley to design the tb unit, gm screwed em and went with rochester to build it. it was gm's property because gm contracted holley to design, not build. holley got screwed, eventually was able to build it without gm getting mad or filing suit.

as far as i know.
Dephi used to be Delco. Declo used to be gm. they are all now spunoff into their own companies so that they could increase their markets. what ford guy wants to admit hes got gm parts under the hood. its ok to have delphi stuff though.

delphi makes the new xm satalite radio tuner. its ausome, they gave one to my parents since they own the gm dealership... it really is too cool. you just grab the thing and take it from your car to your house and its got port station things for both. but anyway.

ive still got the 2.25 inch throttle body design if anybody has 500 to have the first one built. wouldnt do it unless i knew somebody NEEDED it. not sure they do anymore.

 

Hmmm....I wonder who told you that
Going to the track this weekend. Looking for at least a 104 trap speed if not more. Still having troubles with traction. Instead of wheel hop the car just spins through 2nd gear....ugh. I need bigger tires. I've done nothing to the motor, it's still the same thing as before. Only difference is now I've got fuel pressure and LCA relocation brackets. I doubt the brackets will improve my mph but I have a feeling the fuel might.

 

was it.....you?

i couldnt remeber..

good luck. let us know times. i should have my 355 in within the next couple months.

should i , a. put in a smaller cam, or b. have the heads milled for the bigger springs etc.. so i can use the one i have. (over .500 lift).

i might drop some cash and build one of my tbi's. im takin out a student loan for my last 24 hours of school so ill just get a bit more and build a tbi

 

You have to ask?....b of course. or c, which would be definatly not a . Don't get so much cam that the motor is a gas guzling wreck. Do it with style, smallest cam possible is always the easiest to work with. I'm considering doing an Lt1 cam swap in my 350 if I get a couple turbo's for free from a secret resource. Figure I might as well start small and rebuild the motor in a year or two and install a bigger cam.
If you're going to build your TB you might want to just consider going with Holley's newer 4 barrel TBI with the newer injectors. The 2 barrel has that issue with air and fuel distribution where as the 4 barrel doesn't. I'm considering doing the swap just for fine tuning purposes. Having 2 2" butterfly's directing air the way they do just doesn't jive well with me.

 

it probably doesn't jive well with the front cylinders either.

 

I haven't heard from the front cylinders but the rears called me up the other day and said they were pretty ticked off .
In a perfect world I'd have a teliporter and do the 1/4 mile in no time, oh well.

 

The Cross-Fire is a TBI, low profile, large plenum single plane intake with tuned runners. If only the runners would flow a bit better ...

 

JPrevost: What's your email buddy? I've tried contacting you but i think maybe your profile email isn't up to date? Thanks man.

TRP

 

About the limit of the throttle body and cfm, I read in a carcraft new parts review that holley has the 2,000 CFM throttle body for heavily modified TBI injected motors. Ive known about the commander MPI systems with 1,000 and 2,000 CFM throttle bodies but I never knew that these throttle bodies could be used on TBI systems. On the other hand, the commander 950 ,4 injector pod, 4 bbl 900 CFM throttle body looks very much the same to the 1,000 and 2,000 CFM throttle bodies. Can it be possible to use the commander 950 ECM and harness for the 4 injector pod inconjunction with the 1,000 or 2,000 CFM throttle bodies?

 

hibernis,

are you talking about a 2000cfm 2bbl unit? the only ones i know of holley making are all 4 bbl unit and won't work with the factory ecm without serious modifications.

 

Iam trying to find that carcraft issue but cant seem to find it. All I can remember about the part review is the line where it distinctively says 2,000 CFM throttle body for TBI applications. Maybe Im seeing things, but thats what I read.


browsing the holley website ,I stumbled across this:

Twin PRO-JECTIONTM 4-equipped 1989 Pro Street
Chevy Beretta (454 CID). Throttle body fuel injection
units (TBIs) color powder coated neon green with
chrome-plated linkage and hardware

 

yeah, those are 4 bbl units.

 

anyone have a handle on that 4bbl Holley 670? I have searched the web but cant seem to find anything on it........part number perhaps? could my super duper LO3 handle it? its an otherwise stock motor.

-blain

 

dont bother putting a 454 tbi on a stock tbi motor without chip changes.

 

The Holley 670 is a 2bbl unit. The 4bbl units come in a 750cfm and 900cfm form. From personal experiance, a larger tbi is not needed for a stock L03. Once you swap intakes and do either a cam swap or 1.6 rockers, then a larger TBI may be considered, given you have exhaust as well.
I just got my 383 running, and I'm using the holley 670. She is making some mad power! I'm really quite impressed, and didn't expect these kind of results, and I haven't even been able to get on her at WOT yet. If I can fix the traction problems, I honestly feel low 12's is where I'll be at. Having said that, I think there is plenty of potential out of the stock tbi, and there is almost no way you would ever need a 4bbl tbi unit on an L03. If the 670 unit is supporting my engine, I would like to think the stock unit is still more than enough to support a near stock L03

 

anyone have a link to where i can buy a holley 670?

 

seanof30306, I just found the parts review for the 2,000 CFM throttle body, Its in the March 2000 Issue of carcraft Page 65, It pretty much says its 2,000 CFM Throttle body for TBI systems that need to feed applications exceeding 600 hp. Its a four barrel, Its machined from billet aluminum, has a dominator style mounting flange, and has provisions for the TPS and IAC. To use this TB, would you have to use the 4Di ECM and harness or the projection system with the harness for the 4 injector pod? And Tuning for the much added air thats being introduced.Can anyone shed some light on this TB?Of course for my stock L03 this is overkill but its allways good to know, for future build ups.

 

i've got a used one!! $250

about 4000 miles, give me a pm if your interested!!!

 

Your car talks to you too??? I thought I was the only one.

 

the problem with running a 4bbl tbi is the ecm. the one in the car now is only designed for 2bbl tbi units. that means you'd have to switch to an aftermarket ecm or modifying your stock ecm. there are a number of people on here who've gotten their factory ecms to work with a 4bbl, but it's complicated and appears to take a lot of computer skills.

imo, if you're going to put the money into another computer, you'd be crazy to stick with tbi. don't get me wrong, i'm not a tbi hater, but a direct-port injection system is much more efficient. if you have the money to put another computer into the car, you can better spend it on other mods and get more out of it.

go back and read the postings in the tbi section for the past 6 months or so. there's a ton of great information on how to get more performance out of your tbi.

there's no way your 305 will ever need a 4bbl tbi. you'd have to get really extreme with your mods before you'd need more air and fuel than you can squeeze out of a 2bbl tbi.

for your 305, i'd suggest a first stage of basic hot rod mods: headers, free-flowing exhaust, better air intake, new intake manifold, ultimate tbi mods, adjustable fuel pressure regulator, maybe 350 injectors, etc. this would be the time to add a posi if you don't have one and (imo) 3:42 gears. some guys like 373s, but 305's have a pretty good torque-horsepower ratio and don't like to rev. to me, that calls for a shorter gear. just read, you can find it all on the board.

two things:

1) be prepared to be initially disappointed in the gains you get. the heads and cam on your motor are terribly restrictive and hinder performance greatly. save that for stage 2.

2) tuning is absolutely critical with tbi, and really good tuning can resolve a lot of the disappointment i spoke of earlier. there are several really good tuners on here who have gotten their cars into the low 14s, even high 13s with stock cams and heads (i believe jprevost is one, njspeeder is another).

i'd suggest getting everything roughed in, then book a session on a dyno with a wideband o2 sensor to fine-tune timing, injector size and fuel pressure adjustments.

once you've maxed stage 1, you can look at swapping heads and cam and chip burning. again, reading past posts will help you make good choices. im there's no reason you can't get into the mid 13s with your 305 with reasonable street mods.

if that's not enough, you can go to a 350, maybe even a 383. while there's a lot of debate on the subject, a holley 670 or a hogged out 454 tbi should be more than capable of supporting 350 hp ..... maybe more.

imo, if you can't get into the high 12s with 350 hp, you're doing something wrong.

 

I know a 900 cfm 4bbl holley , let alone a 2000 cfm, is out of the question with the stock L03.

 

I wanted to buy the 4barrel TBI setup but I am almost positive that there is no way to make it street legal in Cali. I plan to put a ZZ383 that has the fast burn heads in my car but I am still figuring out the whole game plan. I know I wont get the full potential hp if I use my stock one. My dad says I should leave it on there because the stock TBI is a flawless setup. My dad is a heavyline mechanic and has been one for the past 25 years. He said the most reliable and promblem free fuel setup was the TBI. That was one of the reasons I stayed away from tunned port even though I wanted that at the time.

 

if you're going to put the money into an aftermarket induction system, it doesn't make sense to go with tbi. direct port injection is so much more efficient and makes so much more power.

it looks to me like tbi is fine for under 350/375 hp applications. it's reliable and less expensive than tpi, for example. just compare the cost of swapping a tbi intake to the cost of swapping a tpi intake.

imo, you tune your stock tbi till you run out of headroom, then switch to a direct port system like stealth, miniram or ramjet (although none of them are currently smog legal as they have no egr provision).

 

Dammmm Smog!

 

I've wondered what that unit looked like... Do you mind taking some pictures of it when you get it?

I did a search for the owner a while ago and actually found him but he didn't recall any of the specifics on that car when I talked to him...