70mm tb, or 75mm?

[98COBRA281]

i have been looking at tb's because im still running my stock 65mm tb and plenium, and i dont know if i should buy a 70 or 75mm, when i finish my motor, it will have ported npi's, pi intake, stage 1 cams, and longtubes. and full bolt ons, should i get a 70mm, or 75mm tb & plenuim?

 

[deftsound]

Id say if your not going f/i then stick with a 70mm, there was a thread a while back where we talked about this.

75mm while having a bigger opening thus theoretically allowing more air in at a slower velocity if your not forced induction. While a 70mm if your n/a, depending on the motor and what you have done, has a smaller opening therefore theoretically allowing less air in but at a greater velocity.

It all depends on various factors really, but if your planning on going f/i in the future go ahead and get a 75mm, but if your sticking to n/a with our motors your probably going to see better gains with a 70mm because your just not going to be pushing as much air. There was a calculation we used i remember...

But imagine sucking through a small straw as hard as you can and then sucking through a bigger straw. While you can suck more air through the bigger straw its at a slower velocity than the air from the small straw...

anyway i hope this makes sense, maybe you can find the original thread

 

[98COBRA281]

maybe you can find the original thread

yeah i think it even had the same title, but i had no luck finding it, and no, i am not going FI, because my comp ratio will be about 10.2:1

 

[CobraRed_96_GT]

yeah i think it even had the same title, but i had no luck finding it, and no, i am not going FI, because my comp ratio will be about 10.2:1

10.2 because the pistons you're using?

 

[98COBRA281]

10.2 because the pistons you're using?

yes, -2.66cc dish piston, and a 52cc head= 10.2:1, +/- .2, from head gasket thickness, head resufacing, ect.

 

[BurningRubber]

Unless you are going for bling, stick with something like the Pro Products setup, they can be had between $200-250 IIRC.

Summit Racing also sells a Trickflow setup w/ TB and plenum for $250.

 

[deftsound]

theres nothing wrong with professional products tb/plenums, the way i see it is your not going to be seeing gains past about 5-8rwhp anyway, so why spend twice the money on the accufab setup for maybe a 1rwhp difference

 

[98COBRA281]

yeah i would never think about buying an accufab because of their crazy prices.... so 70mm is the way to go?

 

[CobraRed_96_GT]

yes, -2.66cc dish piston, and a 52cc head= 10.2:1, +/- .2, from head gasket thickness, head resufacing, ect.

Sweet I believe I'm right @ 10.2 as well.

 

[scupking]

I have 75mm, I"m N/A and love it. Let your engine take as much air in as it wants.

 

[BurningRubber]

I have a 75mm and no complaints.

I don't like the idea of the "what ifs" as far as the cars future, so I would be aggrivated to have bought a 70mm instead of a 75mm if it would benefit from a larger TB down the line.

 

[98COBRA281]

yeah if it were a stock heads/cams car id prolly get the 70mm, but with all the work done i think a little bigger wont hurt

 

[BurningRubber]

Bigger wont hurt a stock car either.

The difference between a 70/75mm tb on a stock car is almost nil. Once you start moving alot more air, the difference is obvious.

 

[Winters98GT]

I would leave the stock one on.

 

[98COBRA281]

I would leave the stock one on.

why?

 

[02nightmaregt]

Yea i'd at LEAST move to the 70

 

[Mikie]

Sorry to hijack the thread, but at least it bumps it to the top for ya.
I have a blown application moving alot of air with a factory throttle body. I have just ordered an Accufab 75 for mine that will be here later next week. My question is...

Do you guys think I will need a re tune once I have added the TB?
Damn I hope not as its $250 a whack for updates on my tune.

Any info would be appreciated.

 

[scupking]

Sorry to hijack the thread, but at least it bumps it to the top for ya.
I have a blown application moving alot of air with a factory throttle body. I have just ordered an Accufab 75 for mine that will be here later next week. My question is...

Do you guys think I will need a re tune once I have added the TB?
Damn I hope not as its $250 a whack for updates on my tune.

Any info would be appreciated.

I would assume you would have to. You will be letting your engine take in more air, in turn that would change your air fuel ratio. I may be wrong but that's what I think.

 

[BurningRubber]

At the very least, put it on the dyno to check the air/fuel ratio.

Chances are you will want to tweak a few things, as it will likely lean out a bit.

 

[Winters98GT]

why?

I didnt gain anything with a frp70mm tb on my ported headswap 98. I believe it was .4hp gain. Both runs were done at CXI here in Houston