The 800 twins will not last long if the heads are shaved too much. The pistons will detonate with .020 off and less than perfect fuel. If you must modify, go to a good shop that will guarantee their work, and ask them what fuel to run. If you do it yourself, be prepared to sit when it blows because Cat doesn`t have many parts in stock for the 800. For some reason they don`t have piston pins, bearings, gaskets, crankcases. Very poor parts management.