Ok a freind of mine has a 7.3 powerstroke and put a bankes turbo on it. Now the thing whisles like a semi truck. What makes the turbo whistle like that but the old one didnt? Also Ive seen turbos for sale that are supposed to whisle. Ive got a really good idea but I need to figure out what makes the turbin sound.

I'm assuming your talking about a 99.5+(since you stated powerstroke). The 99.5+ had an impellor in the intake side with larger vanes and more of them to keep the turbo quiet and produce more boost. Prroblem was when you add more power you would get surge and stall in the turbo and lose boost or worse your turbo. So BANKS includes in there kits a 99 impeller(AKA wonder wheel) which has smaller vanes to allow the turbo to spin up faster so it doesn't stall out. It actually makes less boost but it is best for the turbo. But yeah it makes them loud and whistle since it is spinning faster and has smaller vanes on the impeller.