Startingline products has a good pipe or pipes out for the M7. The only thing with the M7 is that you will also have to add some sort of fuel management system. They have some new products out to do that, but they all cost more money then just the pipes. If you really want some good power you should look into some of the big bore kits for it, snowmobile Racinstation.biz has a kit that will turn your M7 into a M8 with a stock pipe it will put out 160 hp with twin pipes it will put out 170 hp. There is a couple other places with these kits, but I have heard good things about the racinstation kit plus they are located out of driggs Idaho so they are close.
Medsker