I have a A4 00' z28 camaro. Wondering the difference between the fast intake compared to the LS6. I heard the only difference is the fast is that it is a three piece intake, and you get alot of whistle. On the other hand the LS6 puts down the same amount of power but, with no whistle. Is theis true? What type of throttle body should i also purchase with either of the two.

 

I assume that you are talking about the 78mm FAST intake and not the 90mm?
A 90mm FAST will almost always make more power than either the 78mm or the LS6 on a larger cube motor or even a stock cubed one with ported heads and a bigger cam...the 90mm is generally considered too much for a stock internal or small cammed motor.
I kind of believe that the 78mm FAST intake will make at least a little bit more power than a stock LS6 intake providing both have the same throttle body on them. Whether or not that much larger expense is worth it is another story.
The whistling issue has been attributed to not having the foam padding underneath it like the LS1/LS6 intakes do, some have corrected the whistling by adding some.
I would (and do) use a ported and polished stock throttle body.