Mostly eveything else everyone said is good. I also say that you should build up to the power you want. Truthfully if you went with a supercharger kit and ran 8-10 psi I think you'd be happy with the power. Especially if you've never supercharged or turbo'd a car before. 300hp at the wheels truthfully is a lot for a street car. And if you never have felt that kind of power you probably wouldn't even know it was 300hp or 500hp. Metrix motorsport makes crate engines that you can buy fully built. Depending on a machine shops labor it may or may not to be cheaper to source your own parts and get a shop to build it or to buy an already built motor. Do not trust just anyone to build your motor. BMW's are not like honda's or toyota's. These cars need people to work on them that know them specifically.
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