The head makes all the difference. You can keep shoving bigger and bigger pistons in but if your head can't get the air in and out your wasting your time. I was just gonna have my stock head done, but came across a really good deal on a V+H pro head that was allready done for cheeper than the stock head job. Did it make a difference. OH YEAH, and now after having the bigger head the bottom end is ready to go as big as i want.