Gday Mike, I was interested as they looked large to me, Im putting 41 mm inlets into my 920,s head to help it breath abit better. The ports have been opened up to 33.5 mm aswell. The valves started out as RGM 42 mm but seeing Im leaving the valve angle as standard, I turned them down .5 mm for a liitle extra clearance.DR-HILLIER pm,d me and said he runs 2 Commandos like this with no trouble, he did say he checked clearances first. The valves used are of wasted stem semi tulip type, the wasted stem Im told is for weight saving rather than better air flow.

Rgds Foxy