Mike said ” what difference do you see between the best pipe and the 3 hole can or the 4 hole can ?”
When Daniel Woltjer sent back my engine it came with a Dyno sheet that read just about 19hp when it was built for a 4hole can(Yamaha Jr.) When he sent the Dyno sheet for a engine he rebuilt for me with a WKA Sr.Y pipe(Yamaha Sr.) it came back with a Dyno Sheet reading just over 22hp. So what I found was roughly 3.5hp advantage but I had to add 40lbs (Jr=320 Sr=360) of weight so although my daughter liked driving it better then the 4 hole can it was a wash time wise on a 7/10 mile 11 turn track. There are however pipes/Headers that make a lot more power then the Sr. Y pipe. A friend of mine put on a illegal pipe that picked up almost 2 seconds over the Sr. Y pipe.