i ran an accufab plenum and 75mm tb for years in my GT and had no issues with it. it really depends on what your plans with the car are. staying relatively stock? n/a build? f/i build?

 

There are no gains with anything bigger than a 70mm, thats why they say for N/A Stay with a 70mm. I have a 75mm because I got a good deal on a throttle body and upper plenum from a member here. I have no bog,no issues. But the extra 5 mm is doing nothing more than a 70mm will do for performance. Youmight even be better off replacing just the plenum and keeping the stock throttle body for that matter, the plenum is where you will see any gain at all.

 

90mm or bust lol jk

 

I have a 75mm BBK on my car, it caused some stalling problems I THINK until I set the throttle stop correctly, now it works just fine. I only have it because it came on my car though.

Remember too big and you can slow intake velocity and that will hurt everything. The 75 will pull harder up high where as the 70 will help more down low. If you wanted to get crazy there are some math equations you can do to determine the exact throttle body size needed for a specific setup.

But as said above, I don't think the 70 will restrict much until you start getting into boosted applications, so is probably the best one to get. But really all that said, you're talking about a few HP/TQ difference at MOST. IMO if you want the polished 75, just get it.

 

Here is some factual information about the 2V engine and TBs and upper plenums, and here and here is info about the backpressure myth.

The issues are similar as the flow of gases (air in the intake and combustion gases in the exhaust) are not continuous streams but rather sort of tear-drop shaped pulses of gas.

For an n/a engine the intake pulses have a lower than ambient pressure head, a near ambient pressure body, and a slightly higher than ambient tail (exhaust gas pulses are the opposite)--and just as velocity of exhaust gas is important so is the velocity of the intake pulses. As the TB get's larger (this is all considering its flow at WOT) the velocity of the intake air charge slows and less mass of air enters the engine--less air = less power.

A 75mm TB is not going to affect this in any serious manner, especially if mounted on the stock upper plenum which is "flow-wise" the weak link anyway. BBK's 78mm combo (8.1% larger than a 75) is likely getting close to too big for an n/a 2V.

 

Can you use a 75mm throttle body on a stock plenum on a 00 mustang gt?

 

You can, but it won't accomplish much if anything, might even hurt. The non-PI engine intake was not that bad on the non-PI engine. It was when they installed the same plenum and 65 mm TB on the PI engines that plenum became the weak link, with the 65 TB being too small once the plenum was upgraded. Even with an aftermarket plenum a 75 mm TB is too big even for the PI engine. Intake velocity will suffer at higher RPMs and more than 65% or so throttle It will cause a torque suck-out at WOT and > 5000 RPM. Do the plenum first...