Somewhere I "heard" or read that the stock TPI throttle body can't handle more than 350 HP! Is there any truth behind this?? I have a desktop dyno program, and with the mods I plan to do to my 383 project I'm showing approx. 387HP at 5000 and 383HP at 5500 which is approx. 1 HP per cubic inch! The ideal engine! I don't plan to upgrade the throttle body, just port the intake and probably port the plenum as well!

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1986 Trans AM
305 TPI
4 Wheel Discs
9 bolt Borg Warner Rear
Completely Stock
Soon to upgrade to a 383 stroker w/TPI, Hedman Shorty Headers, 64cc Pocket Ported Worlds Product Sportsman-II heads, ported intake, comp cam, TPIS air foil, Adjustable Fuel Pressure Regulator, and 24 lb/hr SVO injectors!
Current project: Keeping my car running until I get the money for the above mentioned project! :-)

 

I've heard that the stock throttle body is the least restrictive part of the TPI intake system, but don't quote me on that. See what some other folks say first.

 

it wouldnt hurt to go alittle bigger

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www.irocluke.freeservers.com

 

Actually the most restrictive part on your car is the MAF sensor. It flows a whopping 529 cfm in stock form. Taking out the screens nets 711 cfm! Taking a hacksaw to the aluminum fins inside brings it up to 750 cfm. I got these numbers from two sources so I'm not blowin steam.

Throttle bodies:

Stock 48mm - flows 680 cfm stock and supports 325 hp
52mm - flows 750 cfm and is good to 400 hp
58mm - flows 1000 cfm and is good to 470 hp
Mono-blade- flows 1300 cfm and should only be used for big-blocks

 

The answer is no. A stock 48mm TB can flow even more than 400HP. A 48mm TB flows around 668 CFM.

The GMPP RJ502ci. engine makes 510HP and 550Torque with a 48mm TB.

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Looking For:

87 IROC-Z 350 TPI
84 TRANS AM 305 H.O.

 

joel... take notice of the word least before the word restrictive in jethroiroc's post.


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My `91 Z28 Convertible

 

There's no doubt a stock TB will work with your project 383, but I think there will be power to be gained if you switch to a 52 or 58mm TB, especially with a ported intake. On a totally stock TPI, there's no reason to switch TBs. With extensive mods or larger cubes, a larger TB will help. I went to a 58mm TB and gained 2 mph in the quarter with no loss in low end but much better top end. 2 mph is roughly a 20 horse gain. All these flow numbers are great in theory, but until you have real track times to back them up they are still just theories.

As for the statement that the 502 Ramjet makes 510 hp with a 48mm TB...I think that is misleading (no flames intended IROCZTWENTYGR8 because you are not the only one who has said this). I bet they will gain more if they swithced to 52 or 58mm TB. Of course it'll make over 500 horses...it's a BIG BLOCK!! Cam, intake, and head design have more to do with it's power production. A radical cam in a small block will be mild in a big block. Remember the ZL1 4th gen Camaro with the big block? That thing had DUAL Accel 58mm TBs!!

Just my 2 cents

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

 

IROCZZ3, u got mail!!

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Looking For:

87 IROC-Z 350 TPI
84 TRANS AM 305 H.O.

 

Don't you think GM would put a bigger TB on if it made more hp??? What sells that 502 is hp. What did the LT1 have??? I think the 330 hp Lt4 also had 48mm. Damn you really don't need a bigger TB!!!!!!!!!!!!!