I always found the 2 different philosophies between Yoshimura and RC interesting. Yoshimura believed in lightweight components with extra attention paid to machining and materials. RC was just about the opposite. Heavy,chunky pieces such as pistons/pins etc. In general their stuff always looked crude to me (especially items like the big block). Yosh had the good connections with Japanese companies so they got some quality parts (springs etc).
Exactly!
I always used the Yosh parts for the roadracing (the "ballet" we called it, after the "On Any Sunday" movie), and R/C and Action Four parts for the drags. The Yosh seemed to develop more HP for a given package, but not as much low-end torque as the R/C parts, in my experience. Most riders on the street seemed to prefer the low-end grunt (and dragsters, too), so we always quizzed the owners about their intentions when asked to "build an engine". Most of the roadracer customers just came in and asked for a Yosh buildup, and often knew what parts they were wanting already.
The R/C and Action Fours parts of the early 1970s didn't hold up well on the RR tracks, burning lots of oil and cracking rings. The oil problem at 10,000 RPM ranges was caused by those oil grooves on the piston skirts, for the most part (too much oil for the rings to control in those areas), and the hydraulic action of the oil forcing by would upset the 2nd and 1st rings and make them flutter and crack.
The Yosh pistons were very smoothly cast on their skirts by comparison. Their rods were lighter, and usually weighed EXACTLY the same in a given kit, with a hand-finished appearance, numbered and with corresponding wrist pins, also numbered: very meticulous. The American rods were often tenths of a gram apart in weight, usually with as-cast finishes, wrist pins in a plastic bag together.
We always shot-peened the American rods at the machine shop next door, just in case...
