[pokeybritches]

I had some time today and made a calculator for power gains. It's VERY rough and makes a few assumptions. For one, it neglects the parasitic drag (in the form of pressure loss) due to the throttle plate (skin friction, wake drag, induced drag). It basically shows pressure loss across the throttle body due to the piping diameter and length, since this is the restriction we were discussing. It doesn't take into account resonance tuning in the intake manifold or many of the other things that can affect performance. It's difficult to exactly isolate the throttle body's impact on performance without looking at the whole picture. Take it as a grain of salt.

I don't know what the M54's throttle body diameter and length are off the top of my head. Using 2.5 inches for the diameter and 2.5 inches for the length, I calculated a 0.0738 psi and 1.2 horsepower loss at 8.5 psi of boost. On a stock car, I calculated 0.0426 psi loss for 0.65 horsepower. Increasing the TB diameter to 3 inches in diameter but 2.5 inches long resulted in a 0.0179 psi and 0.27 horsepower loss across the TB (so basically a gain of less than half a horsepower over stock). I've got a rough draft of the calculator available for anyone that wants it (preview attached). I was also exploring how to use the Apple Numbers app at the same time. PM me your email address and I'll send it over since Zpost won't let me attached Numbers or Excel files. I'll clean it up and make it pretty at some point. Constructive feedback welcome.

Remember that the throttle body is like many other things - when you increase the range (flow potential), you reduce the resolution ("feel" and ability to make minute, precise throttle applications). A larger throttle body will provide less accurate response.