Hey Guys I've been watching this board for a while and have a couple of questions. You've convinced me to keep my tbi. I always thought that tbi was the problem with GM 8V performance. Maybe its just me but every tbi car or truck I ever drove(no mods) felt realy strong at 1/4 to 1/2 throttle but when opened up all the way didn't pull nearly as hard as I thought it would. I learned through this board that the heads and cam are the major problems, NOT THE TBI. Living in NY, me and my wifes Fbodys are pretty much put away for the winter(97 30th Z28 6sp, 87 WS6 T/A 5sp tpi) My question is about my truck(hope that dosen't get me thrown out!) It has most the good factory stuff, 95 4x4 Z71 350tbi 5sp 3.73s. How can I get more top end with out killing my bottom end power? It feels strong at 1/4 1/2 throttle but full throttle third gear passing is kind of scary! I know, its a truck, but 96 & up vortec trucks run hard so why can't mine!!! It has all the normal stuff, full tune up with new O2 and cts. Normal mods K&N, Flowmaster cat back. What is my best bet to wake this thing up? I know a cam and heads but which ones? Can I get away with just a cam swap? Thanks, this is the only place that won't just tell me, put a carb or tpi on it. Sorry about the book Andy

 

The L31 Vortec heads are what makes the 96-up trucks run. The older heads are junk compared to what is now availible.

The L31 cam durataion is 190/195 @ .050 and lift is .412/.423. You don't want to get wild with the cam due to the weight of your truck. You need the low end torque to get moving.

Anyhow, get some good heads.

 

Yeah, Vortec heads and Performer 2102 camshaft (.420"/.442" 204/214deg) with Vortec intake an adapter plate will work well for you for less than $1000 and should increase hp substantially without killing low-end/mileage at all.

 

Thanks, I like the vortec heads, but for the money the local junkyard is charging $1100 for a 96 350 vortec long block with 15,000 miles on it. My truck has 50,000mi. Should I just buy a complete motor and swap it in? I've heard that 350 tpi heads are good also, is that true? Would they help for cheap?(could reuse my old intake, might find good set used) I don't mind spending the money on vortec heads but would rather put it into the wifes 87 T/A!!

 

If you can verify the miles (ie 15k not 115k) on the motor and it comes with whatcha need, it's worth a grand... Might have some swap problems, though, that you'll need to check out. Yank the oil pan, too, and look around and at the oil pump pickup and for sludge/grit in the bottom of the oil pan itself. That's tell you a LOT about that motor!!!

 

hey ur from elmira? thats right by me! im in orchard park. u familiar with the area? acctually orchard park w seneca but same difference really

------------------
1989 pontiac firebird
bright red exterior(just repainted)
grey interior
5 spd
305 TBI (stock)
WS.6 formula wheels
3.73 posi rear end
http://members.aol.com/j007golden/Mikey89.html
-------------------------
1985 trans am
factory bright yellow
4 wheel disks
16 inch wheels
305 TPI
power antenna and mirrors
t tops

 

Don't forget the tbi. Go to a larger tbi, say a 454tb or the 670holley and a new dual or single plane manifold. A set of hedders would help complete a bolt on package.

 

You don't need a larger TBI unless you get over 350hp and 6000rpm with a 350 or larger motor, from my DYNO and real-life experience...

Two 1-11/16" holes can flow a lot of air, and that's a fact...

 

I guess he could at least do the ultimate tbi mods with a good aftermarket manifold and headers maybe huh?

 

welcome to the tbi bunch.
my family is from teh elmira area(big flats and horse heads) when i come up this summer we'll hafta hook up.
i don't really believe the need for the bigger tb, i use prepped stockers on my ride and they are working out great. if you do a cam it becomes a toss up. just don't go past .460 lift and you'll be kewl.
lata
tim

------------------
91 Camaro RS-LO3,Auto.
14.215@94.30 w/ 1.917 60'

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

 

Edelbrock flowed the 1-11/16" TBI on a flowbench when they ere designing their MPFI conversion (no injectors anf with injectors) and you'd be surprised at the numbers they got. No I cannot tell you what they are...

You do not need any TBI mods for a moderate performance 350, especially not for a 305, IMO. I am soon to try larger cam(s) with my setup and will let you know when I run out of air. I think HOT cam will be next but I will probably use the stock LT4 cam first so I move in a baby step up from the 3702 Edelbrock cam. Or I'll be PROMing forever and be scan-tool blind. Thank God for scantools that record so you can watch the BLM's on the side of the road or in a garage with a beer, pad and pencil.

 

i need to post once more, 666 posts is a bad number

 

Since this is a truck motor it probably won't see over 4 to 4500Rs. Will better heads help at lower RPMs?(4500 vs 6000) Anyone have any ideas if L98 heads would help? I think their 58cc chambers would bump compression about one point, but is the design better? I'm kind of hoping to use a used set of L98s and a new cam because being a low speed motor I don't think headers and a better intake will help that much. Am I wrong?!? Like I said I think the vortec heads are the steal of the year I just wish they were bolt on and go,(no special intake,rockers,gaskets,ect...) My wife is ready for a stronger small block under her TPI thats where I want to spend my cash! And yes Mr Moderators I'll put any questions in the TPI board! I'm from ELmira and if anyone is from around the area Sat night during the summer we are usualy in the Walmart parking lot in Big Flats. The turn out is pretty good, but since it is kind of a busy area there are no burn outs Maybe we can get together this spring/summer! Well time to brave the wind and snow to find parts for the father inlaws 460 Lincoln! Thanks for all the replys!

 

gm has come out with intake designed for t.b.i. Its supposed to complement the heads. I dont know if compression problems are still an issue. Someone had said the intake costs 320 dollars from g.m. I went down to my local dealer 3 months ago to get a price on vortech heads($220 a piece cheap!) It was then he told me about the developement of intake for 305 t.b.i.er's. I know when i make the purchase i will port and polish everything. I hope this helps!

 

ahusted, vortec heads have the same size combustion chambers as the iron L98 heads, their both 64cc's. FastBroker has a good combo with the standard performer intake (not the rpm) with adapter plate, mild cam. Another option would be to use 305HO or TPI heads with 58cc cc. or the Corvette aluminum L98 heads also with 58cc cc. (these would be the preferred heads, IMO). The Vette heads with the above intake and cam combo would be a good package as well. I also don't think that headers will hurt your low end tq only help your midrange and gas mpg.

Steve

[This message has been edited by steve8586iroc (edited February 17, 2001).]

 

You GOTTA be able to get 300 hp out of a 9.0:1 350 with OOBox Vortec heads, a cheapo 204/214deg .420"/.442" cam with Vortec performer intake, adapter plate and 1-11/16" TBI. With PROM work and adjustable FPR, I suspect. Maybe 325 if you push it/port it.

You don't need special rockers... Go to SDPC2000.com and search on Vortec. They have a KIT that has 2 complete heads, Performer Vortec intake, head/intake gaskets, stainless intake bolts and stamped steel (ZZ4?) rockers/*****/nuts for about $670 bucks. That's not bad, man. You can live just fine with the Vortec springs with the cam I mentioned.

[This message has been edited by FastBroker (edited February 17, 2001).]

 

My dad has a 95 burb same engine as you. Thing is a dog compared to the older 87 burb we had. First I'd get headers. Also an open air element, cam could come but I wouldn't do that unless you swap on the vortec heads. The kit mentioned with the head swaps is great. Do that with a cam to be very happy, don't do one or the other, it won't make a seat in the pants difference and you'll still be wanting more. I'm telling me dad to save up for vortec heads and we'll do a swap later when I give him my intake while I get the air gap version . Does that help? TPI heads aren't great, won't make much of a difference either unless you do a cam swap.

------------------
, Jon (91 RS too many mods to list), getting new engine in summer

 

One of the posts above states that the stock TBI unit is good for 6000 rpm on a 305. I beleive that the TBI unit flows about 400 cfm. If that is correct, it may start becoming a restriction at as little as 4500 rpm with a 305... depending on the motors VE.

------------------
1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter
350 .060 over with forged 1 pc rms crank, and forged TRW pistons, 9.5:1 cr
Factory GM heads Pocket ported, 2.02/1.60 valves, back cut
Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI
Edelbrock Performer EGR intake, Edelbrock TES and 3" cat

 

I bet it does become a restriction at 4500 on a 305. Why else would the RPM limit be set there? its such an oddball RPM limit for an engine that can easily spin to 6500 with the right cam.

------------------
-Tas
'89 Formula WS-6
[soon to be Torch Red with black hood and headlights =) ]

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

Super GRK_Taz World
EFI & Intake Options
AOL IM: superGRtaz | ICQ 82881207

 

I got a 350 with a 1-11/16" TBI runnng to 6000rpm with no vac signal on the ECU (ie MAP of 100) or on a vacuum gage in the dash.

Don't need the 670 cfm for a 305, IMO, or for a less-than 350 hp 350, either, and I will rve it. And it flows more than 400 cfm, too, for sure...

[This message has been edited by FastBroker (edited February 19, 2001).]

 

FastBroker, how much boost are you running?

 

DOUGH! Seriously... Call Edelbrock yourselves and ask around... You'll get the numbers of the OEM TBI. More than 400cfm... MUCH more! Go to an engineering book and eee what the cfm of plain flow of air through a hole 1-11/16" is an multiply it by two. you'll be surprised. Yeah, yeah, the throttle plates/shafts in the way... big deal. They got you all fooled to make money.

 

Let me start by saying that my intention is not to flame of insult... for educational purposes.

If you just want to consider port area and accept that the 2" bore unit flows 670 cfm, the % area difference would imply that the 1 11/16 bore unit would flow 478 cfm. A little more realistic model would also account for valve size as a % of bore and % of airflow against the walls of the port... both % numbers will go in favor of the unit of the larger bore. Also consider that the injector is in the airflow path and poses less of a restriction to the larger bore. I'd see this as the largest restriction. Add all this up and the 400 cfm approximation I keep hearing seems reasonable. Of course all this is based on the 670 cfm rating of the 2" unit being accurate.

Now, a 350 ci at 100% VE at 6000 rpm flows 608 cfm. If we assume that the 1 11/16 TBI unit flows somewhere between 400cfm and 475 cfm and that it is not a restriction on your motor... that would make your VE 66-78% at 6000 rpm.

Maybe I should take one for the team and take my stock TBI unit to the local speed shop and have it run on the flow bench.

EDIT: also keep in mind that there is more to air meter selection than just max airflow. Motors with dual planes like 10-20% more airflow than single planes. More airflow capability (with the correct fuel) can also aid throttle response and acceleration.

[This message has been edited by Dan W (edited February 20, 2001).]

 

my 305 was pulling about 2" of vacuum at 5800 rpm with the 1 11/16 bore throttle body on a single plane

and it wasnt even near tuned right

I dont see any vacuum with the bigger throttle body and its now tuned right

 

not to say that you cant make big power with the little throttle body, heck, hotrod ran 13.8 with one in an RS

 

Have one flowed... That will put this to rest!!!

I'll bet it (1-11/16") flows about 600-625cfm and the 2" about 775-825cfm, both with pods...

A 4bbl Holley 1-11/16" venturi bore flows more than 1025cfm, and that's with all 4 BIG BIG BIG boosters in the way and necked venturies around the boosters. I think you'll all agree that this could EASILY flow 1200cfm with the boosters removed and probably MUCh more, right? Cut the conservative 1200cfm in half and what do ya' have? 600cfm. IMO. Oh, and that doesn't even include the removal of the turbulent effects of the venturi neck-down restriction in the carb (for booster operation), which doesn't exist in our TBI's...(ie, 1-11/16 venturi and booster combination going to 1-13/16" throttle bore will flow less than straight "tube" of 1-11/16" with no venturi/booster interference)

Let us know if you have one flowed.

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

 

I have a carter 625 cfm carb, i measured the area of the most necked down spot in the venturi
added all the area up and its a hell of alot more than little TBI.. i cant remember the numbers
granted im not taking into account the boost venturi but by the same token i wasnt taking into account the injector pod on the little tbi unit either
I worked it out as a % difference and it was consistent with all the 400 cfm figures ive seen... i think i came up with 429 cfm for the little tbi
not exactly scientific, but something for you folks to consider

and i wasnt seeing things when my vacuum gauge climbed to 2" by 5800

i should say there is much to be said about the turbulent effects of the boost venturi but by the same token theres much to be said of the injector pod too

[This message has been edited by Pablo (edited February 20, 2001).]

 

hey pablo what do you think about what I said before?:

 

i think the cam has more to do with it than the throttle body

 

Remember, guys, 4 x 1" holes will not flow nearly as much as 2 x 2" holes... There is TWICE as much flow area in the 2 x 2" hole scenario... So, SIMPLY adding up the hole sizes of a crab, if that's what you did, Pablo, will not give you real life numbers.


Also, 4 holes that equal the same flow area of two holes will still underperform the 2 holes because of physics. Ie, the 4 x 1" holes above would underflow 2 x 1.414" holes even theough their flow area is the same.

 

No thats not what I did, I added up the area of each hole

it was substantially greater than the little tbi
granted the boost venturi take up same space and disrupt airflow, and, obviously 4 holes with the same area as two holes will flow less just because of frictional losses
that said, it was still a hell of alot more area and i dont think the other factors could flip it in the small throttle bodys favor

 

But hey if it does flow 600 cfm then great that means you guys can save money on a TB unit

 

BTW, a member on the GMECM list has actually flowbenched the 454 TBI.. i forgot his name i think its walt? forgot his last name.. i know he has a 454 SS truck

he said he flowbenched it himself to 670 cfm at 3"hg

 

I just found a reference that states the 11/16's holley units flow 400 cfm. This is out of a 1998 holley catalog.

PN 502-3, emissions legal Street performance 1985 1/2 - 1989 GM truck 2.8L V6 engine.

Stock for this vehicle is the 1.38" 2bbl that flows 275 cfm. The holley 1.68" unit flows 400 cfm. They advertise that on a 1986 s-truck, the stock unit makes 100 hp @ 5000 rpm, the holley 123 hp @ 6000 rpm.

 

Holley/Weiand also has two 4bbl TB units used for MPFI (nice) that flow 1000 and 2000cfm... Their bores are .75" and 1.25" repectively. These are more like the flow our TBI's will see, ie no venturi effect req'd. Go figure those flow numbers out... WOW!

I am starting to think that the flow numbers for holley/others were had from different parameters on the flow bench. Any comments? even I find it hard to believe that their 1.25" 4bbl can flow 2000cfm. It is pretty sweet, though, and the 1000cfm looks better, actually.

I'll do some more research and get back tomorrow.

EDIT: Just saw Pablo's post.. That 3"Hg flow number doesn't sound right to me, ie cfm numbers were done under different flowbench parameters, not 3"Hg. I believe we have some inconsistancy here. We'll get it figured out. Either way, I've been in a 390cfm 4bbl car that made 500+hp that ran with a little vacuum pull on it at max throttle. Still ran pretty friggin' good. We'll get it fig'd out. Just stop this market from lowering my net worth, PLEASE!


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

 

Just wanted to correct that I meant 1 11/16 not 11/16 as I said above.

 

ive always seen the tbi units rated at 3"hg as opposed to 1.5"hg like carbs which would actually mean they flow less than they seem ( I dont buy that either.. it seems real fishy)

i think all two barrel carbs are rated at 3"hg too thats probably why they tested the tbi's that way

 

E-mail From Turbo City... he didnt send the pressure they are flowed at though.

_____________________________________________
Hi Dan,

Stock 350 TB = 520 CFM

Hi Flow = 590 CFM


At 12:55 AM 2/20/01 -0700, you wrote:

I'm doing some research for a modified TBI motor. You advertise a high flow
TBI unit but I didnt see any actual airflow numbers. How many CFM does your
high flow unit flow and at what pressure? Are these high flow units bored - Yes, Vic


out and do they utilize a larger throttle blade? For the sake of curiosity
do you have flow numbers for the stock TBI units?

Thanks
Dan Workman.

 

Here is the next e-mail.


------------------------------
Hi there,

Sorry to say, but that information wasn't provided to us.

Please keep in touch,


Vic


At 06:23 AM 2/23/01 -0700, you wrote:

Thank you for the information. It would be very helpful if you could tell me the pressure these measurements were taken at. IE 28" of water or 3" of water etc.

 

500 - 600cfm sounds right. I just beat the heck out of my motor this weekend for some scan tool PROM tuning and no appreciable MAP signal (ie, MAP below 100) up to my 5800-6000rpm rev limiter. 350 with pretty mellow cam, though, 194/214 with .396"/.442", but still, 350 cid at 6 grand...

 

Do the 350 truck TBI's have 1 11/16 bores?

 

Dan, Fast, Pablo, If the stock unit is 520 CFM, what will that Limit HP to in a 350?
Is that an over simplification?........bob

 

Not sure it will limit HP at all as there are 350cid race engines with 390cfm four barrel carbs and/or 500cfm 2 barrel carbs making over 500hp. Yeah, that is carb-to-TBI comparison but c'mon, guys.

I agree that no vacuum signal at high rpm's will get you more hp and get it quicker but I'll bet that the same engine with either TBI unit will perform similarly well, with PROM tuning the deciding factor in which is the faster, the better daily driver and the better mileage getter.

If you guys didn't see the other post, my 350 with 194/214 deg and .395"/.442" cam is not pulling any vac signal at 6000rpm and dynoed at 245hp. Yeah, it is a MELLOW cam but this engine can PULL like a dickins from idle to a little below 4k. Just got HOT cam and am either gonna try it or 214/224 SIS cam like Pablo's with 1.6's and see what I get. Looking for 300hp dyno and I should get more. I will probably try the 214/224 first because I am new to GM ECU PROM tuning and need/want to take baby steps in the cam/config changes.

Any hints on cam choise? Anyone use HOT cam w/TBI, yet? Anyone want a HELLA spark curve for 350's???

 

yes everybody but the 454's had 1 11/16 bores.

 

Depends on how efficant the motor is and how high you plan to rev it. A stock motor will not be hurt because of the low VE's they run at and the low RPM's. A highly modified motor will be hurt by it. You are probably somewhere in between and most likely, be loosing some power in the upper rpms. Its not as if you are going to hit a wall... more likely you will just loose a little on top... it might not even be noticeable.

You might go check out a post The ODB made on the TPI board about TPI and HP limits as he talks about this in length.

Fastbroker, Come on, you know as well as I do that the whole reason those cars run restrictor plates is to limit power. With a
larger carb those cars would pick up huge power.

 

Never argued that point. Just saying that they are "restricted" from huge hp levels down to still huge HP levels and we are comparing our engines to that when we have less than 1/2 of their output.

Again, IMO, a 1-11/16" TBI unit can handle a 350hp 350cid motor with ease up to 6000rpm. There is no need to go over 6-grand with a 350hp-400hp 350cid motor. Honestly, you all should know that 350hp is a relatively mild 350cid, and 400hp is not too much of a stretch beyond that... I plan to prove this, too, instead of just talking and theorizing about it. I'm at 245hp now with a mellow cam and next cam coming in a month or so. anyone else out there have dyno DATA??? I'll take chassis OR water brake, whatever you got.

Anyone think I can get 300hp with a 204/214 .420"/.442" SIS generic cam and 1-11/16"? I have carbed several above 300hp with that cam and 9.0:1 CR/heads/headers but never a GM TBI... Anyone else done the combo before?

 

FB, the Nascar engines that make high hp wiht a small carb is largly due to the 14-17/1 CR that they run. They also run lean and if not careful they burn a lot of pistons. You'd be amased at what you can do if you run a high compression ratio. I just wish we could buy 100+ oct gas again.

just my .02

 

My point is not CR, it is the volume of air that the engine needs. Nascar motors need lots of air, don't they?

 

FB, my point is to make the HP they need to run superspeedways speeds they must run ultra high compression engines with the small hole restrictor plates. If the restrictor plate was removed then the CR could come down and still make more HP. And yes they do flow alot of air but not as much as you think. To make the HP you want and still keep the small tbi you would have to increase the CR to levels to high to run safely on pump gas. One more thing to take into consideration is the cam specs witch would also be a major factor to running a small carb or tbi.

[This message has been edited by steve8586iroc (edited February 28, 2001).]

 

steve 8685, I gotta ask, given a small carb or TBI in general what type of cam specs do you need to look for to maximize HP/torque and still be streetable. Thanks........bob
I hear ya on the compression