kmcray85

I dont know too much about the performance parts, but I want to get a TB and plenum combo. What is the difference with the 75mm and 70mm? What would you recommend for an 03 GT auto. I am getting 3.73 gears installed this weekend to go with my k&N, flows and 93 brenspeed tune. I DO NOT plan on any forced induction.

Thanks

black35th

Most will say to go with the 70MM, IMO though, if they cost the same then get the 75MM.

I went with the 78MM BBK unit, but I plan on some FI later...

marcuslee842

Did u notice a power decrease? I have a 75mm (don't plan on 78 anytime soon) but I installed that the tb, cai, and predator tuner and I felt a difference but it was probably the firmer shifts from the tuner.

black35th

No not a decrease, not really an increase though. Great throttle response more than anything, I also have a CAI.

marcuslee842

OIC, alot of people say that bigger than 70mm hurts our performance. I don't think it has a negative effect that is noticable, or one at all for that matter. I always thought the heads would always move a certain cfm of air no matter what, unless u are F/I of course. It just seems like the heads would make the same cfm of air in from a 70, 75, or 78. It seems like it should not improve or decrease performance unless F/I is introduced. I'm pretty sure someone who knows there their will stuff correct me. Atleast I hope so, I try to learn as much as possible about my car.

SilverGT03

I will be ordering my 75mm come monday

marcuslee842

Sounds good! What brand are u getting?

black35th

I'm sure CliffyK will chime in soon. They say that the bigger the TB the less intake charge it will have and it will lessen the ability for it to "suck" air in, obviously that isn't the scientific reasoning but more or less the basic. Personally, I can't see it making that much of a difference. The difference between a 70MM and 75MM is just over 3/16's of an inch. The difference between a 70MM and 78MM is 5/16's of an inch. We're talking some pretty small differences here IMO.

Once you go FI, that all goes out the window of course. A blower forces air through the intake, that's how you get "Forced Induction". Like I said, I know I'm going with FI somewhere down the road and it seems senseless to buy something twice.

SilverGT03

Most likely Professional Products. They're inexpensive and a bunch of people on here use them and have no complaints.
Latemodel has the t/b and plenum for $219 so I'm doing that

black35th

Yup the only complaint I've ever heard was about the TB, a couple people had to take a file to the hole where the throttle cable slips in.

Just a little heads up about LateModelResto, call them and make sure they have it in stock BEFORE you place the order online. I've tried to order numerous parts through them only to find out a week later that they are on backorder.