D-man does have those 60mm pistons for a 650 head. They need a large dome to fill the large combustion chamber, no other choice. I don't know anyone who uses those pistons but a friend I race with bought the 60mm 1:11.5CR 550 pistons and his engine makes the same power as mine. Among other people I spoke to Buzz years ago,
before he started with any 550 stuff, so I designed my own pistons and had them made.
Dr. Tom Marquardt ran his 550/650 out to the AHRMA class limit of 685cc. It was a potent combination of bike & rider. He doesn't race it anymore though. He told me he always had leaky base gasket problems at that bore size.
I think with some work my 572 could make 75rwhp, but those extra three ponies come at a high price. At this point the engine is dead reliable, and actually quite docile. I'll not mess with it .....for now! I thought about building a 550 based engine to use with a 650 head. That piece is vastly improved over the 550 head and with even larger carbs should easily push HP into the low eighties. The problem is dealing with various engine components originally built with 36-38HP in mind. I expect reliability issues would surface.
. You'll possibly have to make a pipe for that head, I don't know of any available?? The Kerker primary tube diameter is larger so maybe it could work, I never tried it against a 650 head.
My wife's 592 (61mm pistons) is a mild 51rwhp (stock carbs etc) but ended up being exactly what she needed, a wide power band, easy to ride, just like the original only with 27% more power. It's no pouch! Keep in mind the more power you make, the narrower the accessible power band becomes especially when you get into large carbs. Not that it becomes really difficult, but needs to be ridden differently on the race track.
