[Eatoniashoprat]

It will only cause increased lag between shifts, though this is where you don't want lag. Also not running a blow-off valve will shorten the life of the compressor. The pressure wave that propagates when the TB is closed and after being on full boost makes its way back to the turbo and can cause compressor surge. The main thing though is keeping the pressure wave away from the turbo so it stays spooled for the next shift. Now I'm not sure about carburated turbo setups. I know diesels don't need a BOV because there is no throttle body. Turboed automatic cars and drag racers who speed shift also don't need them because the throttle doesn't close during shifts.

Mike