what kind of gains can i expect from a 62mm throttle body

[skeeterone2]

Ok. i have a 92' 3.1MPFI lumina it has custom dual exaust (dual glasspacks) great sound. i have a k&n airfilter and thats it and i am lookinging to get a 62mm throttle body for my car. i was wondering what it would take to port out my manifold... if i can do that myself. i would also like to know what kind of gains i can expect from this. also i would like to know what kind of side effects i could encounter. thanks... and if there are any other worth while upgrades for this engine at this point i should think about, that would be nice to know also. I figured that with the free flowing exaust and intake i should feel some difference... i just need some relative numbers.
on another note i am also changing my dash... and the plug is totaly different from the dash that i got and the dash that i have right now... right now i just have the granny 85mph dash with the fuel gauge. i have in my possesion a 92 z-34 dash... all the wires are there i just need to move them all around... i dont know if this is going to work at all or not, so if anyone has any expirence with this it would be much appriciated. my car has 56k on it and i have time to work on it so i would like to fix it up nice. thanks.

[geoffinbc]

People who run the 62 TB say they lose power due to intake velocities slowing down...

Sometime too big is bad.

[skeeterone2]

i dont know why the intake velocity would slow down though?

[robby1870]

Yeah, especially on a motor with no internal work

[SappySE107]

Ive only heard positive things, and better track results.

[skeeterone2]

okay i dont quite get the velocities slowing down... the engine is still demanding as much air so if anything the velocity would go up with the bigger throttle body because of the increaced air flow.

[bszopi]

Air moves faster through smaller openings, and the engine can only suck in so much air, especially in stock form.

[SappySE107]

TB size has an impact on engine performance beyond what the engine can suck. There is a correlation between plenum volume and TB size, so a smaller plenum area (like the gen 2) would have better use from a larger TB. I haven't read much on it lately so I have forgotten the formulas.

Velocity may be hurt at the TB, at low RPM, but the plenum is a buffer area, and the velocity in the runners is going to be much higher than the at the TB anyway.

[highoctane]

hey where do you plan on getting one of thee throttle bodys, i was also thinking of going larger?

[geoffinbc]

I remember Raven switching from his large TB to a small one at the track and running a better time.

Maybe ask him and he will give you the low down.

[1QUICKHATCH]

I remember Raven switching from his large TB to a small one at the track and running a better time.

Maybe ask him and he will give you the low down.

thats because he is running a turbo

[skeeterone2]

RSM racing has a direct replacement for your stock throttle body... although you would need to port your manifold for the air to flow correctly... but that isnt a big deal. does anyone know where to find information on this... this velocity thing is really blowing my mind. ok here is how i see it. you engine demands the air... so if you have a bigger opening for the air to pass though the engine can get more air more efficiantly... i need to find out what my intake valves can handle i guess... because that is where it all stops if those are already working at 100% flow with the current TB then there is no point to a bigger one but if they are not i guess a bigger TB would be better... im just trying to piece this together. and yes i agree that air moves faster though smaller openings... but if the engine isnt getting all the air it can through that hole than the bigger TB would be better because it would enable the engine to suck what it needs... and i dont think that it woud affect the low end at all... because the TB is only part way open at that point anyhow and the CFM would be the same as the old TB only it wont be open as far because its bigger? is this right... i am not sure but this is what is going though my mind when i think about it all.

[gpse3400]

Take into consideration the power production bias of the STOCK GEN 1 and 2...

There is HP to be gained but torque needs a relatively faster flow of air. In an attempt of drawing in the same amount of air at a bigger bore will slow velocity down, yet the quantity would be there for HP. I figure that if the engine doesn't really need the bigger size, then there would be a drop in torque and a slight raise in Upper HP at WOT. It would respond more at the part throttle opening compared to a smaller size due to the bigger bore but at WOT it could easly mess up everything below a certain rpm, effective enough the 1/4 mile run would be lost, worst case scenario, kinda like too big of a carb. I guess you wont know till you try though. I really haven't heard anything bad about the Bigger TB, though on the GEN1 and 2 I'm kinda skeptical. I know that removing/altering the airbox on a GEN2 stock to a point engine in a W car for example nets much worse results.... To the loss of .7 seconds difference in my tests. All I can say is that there is a good chance you'd feel better response at part throttle. But at WOT it might bog. Try it, and see if you like it.

[RidgeRunner]

I've been driving around for the past 45k miles with a 62mm TB on an otherwise stock Gen2 3.1 MPFI, and my butt-dyno sez it makes more peak power, and is more "dynamic" in that it's not JUST a "grunt motor", it feels like the power band has been broadened on the high side.

[SappySE107]

https://www.fdpperformance.com

Its a billet piece, not a bore out stock version. I think there is a 65mm version coming out, but I havent talked to kimmo in a while so I dunno what is going on exactly. Franz wont be back on the forums for a couple months as well.