At what point does the stock throttle body (52mm?) become a bottleneck? At what point does the 58mm? Any bigger sizes and their limits? I'm getting the setup in my sig. and wondered if the stock throttle body would be the bottle neck in the intake and if so, what size should I get?

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89 IROC 350 TPI, 700R4, 2.77 9-bolt w/ full exhaust, some bolt-ons, and free mods-G-Tech timed 14.8 @ 96 w/ terrible tires...Parts currently being shipped: AFR 190's, SuperRam, LPE 219/219 cam, Vigilante TQ converter, a "beefed up" 3.23 10-bolt, and some Spohn suspension parts

 

I thought stock was 48mm, i maybe wrong though

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88' GTA 350 MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass

 

Stock is 48.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

TPIS used a stock 48mm and made 375hp. I 52mm might ahve helped a little. The 48mm flows 670cfm, and is a dry flow which is comparable to a 750cfm carb, which is wet flow. A 58mm is probably only useful over 450hp.

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89 Transam GTA, 350TPI, auto, 3.27 rear, dual cats, gray.
Magnaflow cat-back,
K&N open element,
Best E.T. 14.63@95mph

 

Not to mention that a 52 or 58 TB will kill bottom end tourque if you bolt it on without the engine (not the driver )needing it!

 

I'd say stick on the 52mm once you have replaced your intake, runners, and port the plenum.

The 58mm is only for high-revvin' or big inch engines like a minirammed 355, a 383 or a 406.

 

I gained 2 mph in the quarter with no low end torque loss when I went from stock TB to just a 58mm TB. But I also have a SR, AFRs, ZZ3 cam, etc.

BuckeyeROC,
Here's what I've always said in the past based on personal experiences...

LTR setup with ported plenum...52 mm.
SR or MR intake...58 mm.

I think with your planned combo you should go with a 58mm. The throttle openings in the SR are 58mm anyway so I'd get a matching TB.

And I'm sure someone is gonna chime in and mention how the Ram Jet 502 is using a 48mm TB ...fact is, it's still a big block and makes it's power from big heads and big cam made for a big block. IMO GM used a 48 mm TB because it's a readily available production piece.(less $$)

Just my 2 cents.


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1989 IROC-Z, ZZ3 shortblock with some bolt-ons.
13.20 @ 108.69, 2.2 60'

[This message has been edited by IROCZZ3 (edited July 06, 2001).]

 

i saw in a hotrod mag article that the only downside to a large tb was the larger you go the more sensitive the trodle will be and they recomended using the bigger one

 

Look I added a 58mm TB to a 355 Using an SLP cam, 305 heads(dont ask dont feel like explaining future plans) Ported INtake and Full exhaust headers back, and other things all over the place. I went from the stock 48mm to an Eldelbrock 58mm unti an got nothing but gains everywhere. You guys act like we are dealing with a wet flow system. The Tb will do nothing but affedct the vacum in the Plenum. Unless you are using a speed density system thiw will only affect your brakes, so what press harder. On a maf car there is nothing that it will bother performance in the intake because you will still flow as much air as you heads and the rest of your intake allow. Your just removing another resriction in your intake track. If allowing more airflow by increasing you TB causes performances losses at low RPS then why doesnt Cutting your airbox open, modifying the MAF, POrting everything, and what ever else doesn't do the same thing. It all increases airflow.

Will someone please explain this to me?

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89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555

Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!

 

In Lingenfelters book he states the"58mm TB starts showing a significant power improvement on engines making over 350 horsepower".

At the same time he is trying to sale you one though. Im using a 58mm on my 406.


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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

Buckeye wanna sell me your 9bolt?

 

just like a carb, buy one that flows too much, and its worthless, the 52mm should be used with stock or modded engines, at least thats wut it says in my summit racing mag.

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88' GTA 350 MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass