6,500 is where the power peaks and then falls quickly, so turning it any harder is not necessary. It would go higher but the cam would have to have alot more lift and then the compression ratio would have to come down some. Or a meeting of the parts would happen. Also too the engine is cammed for the heads and the flow that they have. So adding a larger cam to this engine would be a waste. Thats whats so nice about this engine, it makes alot of HP and TQ without the high $$$$$ parts. I'm going to be doing one for a customer for the street with 10.5 compression next month.