[Firestarter]

Sorry for resurrecting this old thread. But there is so much misinformation.

Cars don't come with blow off valves. They come with bypass valves to recirculated compressed inlet air to intake to prevent compressor surge. Diesels don't have throttles so this is very difficult to do.

Turbos raise engine efficiency. The manufacturer needs to do gearing and other changes to take advantage of this. This is why all BMW's are turbo'd now.

The wastegate is to keep turbine speeds and boost in check.

On cars like the wrx. They lower compression to increase engine longevity which lowers mpg. They could keep high compression but there would be no boost or need race gas.