Whether or not the actual throttle plate opens 100% is not relavant.

Here's why:

I used to have a supercharger on my car which I ended up removing. I kept the boost gauge, however, to use as a manifold pressure gauge in conjunction with when I use Nitrous. I can tell you that with the pedal floored (even without nitrous), the intake manifold pressure does go to full atmospheric ( 0 psi) on the boost gauge. As long as full atmospheric pressure is being reached inside the plenum, how much the throttle plate has to open for this to occur is really irrelavant. What this does tell you is that the Z throttle body is already slightly oversized and there is nothing to be gained by getting a larger throttle body if you are using stock engine management.

It's all about the E C U !!!!!!!