Hey im almost ready to drop my L31 vortec roller motor w/TPI in my 86 T/A. I have a question though, should i get a 52mm throttle body or dont even bother. I know i should match the throttle body with the horsepower but im not sure if it is definitely worth it. Ive read that the stock 48mm throttle body is good up to 300hp, and the 52mm is good up to 400hp. If I do get the 52mm does that mean i should go with aftermarket runners as well? I am getting an aftermarket prom chip as well. Ive read with the cam i have i should modify the TPI w/ an aftermarket chip. Maybe i should just go from results and go with the stock throttle body first and then upgrade to a 52mm and see if theres a difference. I dont want to hinder any performance thats already in the engine, I just want to be sure when too much is too much. Any insight would be appreciated Thanks,

 

Found this and it talks about your question. As in everything else, everyone has an opinion. after I read this, I figured it can't hurt, BTW, my 305 TPI has a BBK 52mm TB, Ported Plentum, SLP runners, siamesed Edelbrock intake, Compucam, S/R torquer heads, headers and 3" exhaust. With all the intake/exhaust increases, my SVO 19lbs injectors can still keep up, per my AutoMeter fuel ratio gauge. You will not get a huge increase in power, but you will gain some. Not the cheapest 10hp increase you can do, but if your going to tweak the motor, more air can't hurt. Below is the tech note:


A stock throttle body inlet is 48 mm in diameter. The matching inlet on the intake manifold which it's attached to is about 52 mm. Therefore, you can safely buy a 52 mm one (like that from TPIS) and bolt it on in place of the stock one without any other modifications. Anything larger (like the 58 mm job from Lingenfelter) would require the intake manifold to be bored out to handle in the increased volume of air. The larger throttle bodies are not physically larger, they've just been bored out making the openings larger.
The additional amount of HP from the 52mm throttle body is questionable. Some reports show little or no increase, yet others claim up to 10 more HP. And some air foils (to smooth the flow through the throttle body) claim to get another 5 HP. But even that is questionable. A 58mm throttle body (in conjunction with the bored intake manifold) might provide a larger increase in HP, but once again, results usually vary.


There you go!! You decide. BTW, they say that bypassing the tb coolant from running thru TB is worth 5HP or so. If you drive in the winter you might not want to do this, if it is a summer car, I would for sure. Why heat intake air with heated fuild from the cooling system.

 

the stock one is fine