I am the original owner of a 1989 GTA with a 5 liter TPI engine with a 5 speed manual transmission. A year ago I installed a new 5 liter long block from GM and had a Comp Cam and Heddman Hedders installed. The catalytic converters are gone with a 3" exhaust pipe emptying into a Walker super turbo muffler. A Bosch mass airfow sensor and K&N airfilter have been installed. The stock twin 48 mm throttle body is still in place and the plenem has not been ported and the two humps have not been ground down. My questions are: 1) with such a set up would I benefit from a twin 52 mm or 58 mm throttle body and which one both BBK and Holley make these; and 2) would I necessarily need to upgrade my stock 19lb/hr fuel injectors with a bigger throttle body. Once I make this throttle body decision I will complete the engine with a modified chip. I have received mixed opinions on whether a larger throttle body is required for my engine set up. I would appreciate some opinions and people's experience on this subject. Thanks.

 

In your case I would stick with the 48mm throttle body. With your 5.0 liter engine the 48 mm will flow enough for all your needs.

 

I have a stock 48mmTB.


383 motor, check sig

 

this has been discussed many times
try using "search"
and no you dont need a bigger TB

 

Hello BC GTA your factory 48 Tb is plenty fine but what you need to do is get a sharp long object or screw driver and scribe the inside of your plenum on the outer inside edges of the throttle body blades.
Buy a upper intake gasket set.
remove your plenum
and port the front of your plenum to match the stock intake side.
When you get to the rest of the holes open them all as wide as you can making the edges smooth is probably more important than making them wide . "Wider is better"
You can also remove the screens from bothe side of your MAF sensor and possible hack saw off the aluminum fins inside if you have the patience.
you can also get 4 inch flexible intake tubing from the auto parts and some black electrical tape and run you a cold air tube from your air filter housing to the under side of your fender.

 

Thanks everyone for your input. I have decided not to increase the size of my throttle body.

 

Wow, someone who punctuates, and spells correctly!!!!

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