turboguzzi
Come to think of it, my race bike was a 590 for most of its life so it could have been action fours or ?? pistons, I had several bore kits? I do remember seeing "Pops" cast underneath a piston once, just not sure now where I saw it? I must have at least one Yosh piston set?
I got the yosh ported head second hand but have no reason to doubt it was done by Yoshimura. It sure didn't look very radical. Before that I was running a stock head that was just cleaned up and matched prior to installing the yosh head. I didn't remember a significant power gain? Maybe the basic port cleanup I did was lucky? I need to compare them better now and find the differences? Maybe do silicone castings, then pull and compare them?
I do remember the biggest gains were after I installed the Yosh pipe. The TT special cam really loved the shorter primary tubes. All other headers for the 500/550 were designed for street motors. The Yosh pipe didn't work great with mild cams but came alive with the TT cam.
My parts are 1200 miles away for the next 5 months. I live in MI and winter in FL. I'm not ready to part with anything yet, but will share any info I can