XR Valves

Craig Weeks, What mm sizes can one get the intakes? I want 44mm intakes and if a no go, who do you recommend in turning some down,been looking at some Ducati 1000ss valves that look promising,just gotta locate their height dimensions.

Schumann motor works?

I've emailed this guy in the past with no return response,will find someone for this head project.

Jack, Harry Lillie used the valves from the initial 1972 alloy XR750 as models for his combustion chamber design. He later had copies made in slightly larger sizes. The ones I've used that came from the original stock of parts he sold me are typically 37mm (or slightly more) for the EX and 42mm (or slightly more) for the IN. You can go bigger, of course, but these will support 73 RWHP. Harry told me the XR back shape was really good and he pretty much copied that throughout his XS engine building activities. I don't know, but the Duck valves may be optimized for a somewhat higher RPM and superior port shapes than what you would generally see in a modified XS engine.

Craig,what am I looking at in price? New Virago valves would be around 300+ not the quality of the Lillie
valves.

If I were looking at updating the valve train I'd purchase (used?) IN and EX XR valves from Darcy (darcyracing.com) or a flat tracker who runs XRs and copy the shapes on either a new set of valves from, e.g. Kibblewhite, who will make small batch or one off valves from their inventory of blanks, or use a lathe to cut down suitable valves. If the engine isn't a max effort with severe cam ramps, high spring pressures and extended periods at 8000+ rpm there shouldn't be any breakage problems and you'd have valves with shaping that reflects current flow thinking. Harry didn't do any further XS engine development after the late '80s, so I have to assume the ongoing effort to keep the XRs competitive has resulted in some flow advancements since then.