With 735 horsepower and a Dinan-tuned suspension, the CarBahn BMW M4 is a precision-guided sledgehammer. Okay, so what the hell is a CarBahn? And what does it have to do with this $135,000, ...

BMW claims 503 horsepower in M4 Competition tune, but dozens of easily googled dyno charts reveal the peak power is closer to 550 hp. The torque number seems to be accurate; BMW states the engine ...