Dyno's were few and far between in 1980, especially on my budget. I ran one season as a 500 with stock compression and clearanced pistons to fit the class. Then a few seasons with yosh 590 pistons. It was definitely very "cammy" and had that unique sound a radical cam gives. it had a real turbocharged feel and came alive after 8K. I used stock sized valves but a Yosh ported head. Like I said, the biggest improvement was when I switched to short headers and intakes. I believe then the pressure wave tuning of intake/exhaust finally matched what the cam was designed for and the top end hit became more intense and the CR gearbox started to make sense too.
I figured those Yoshi guys knew their stuff but most people didn't run the full compliment of parts to get the full effect. You either saw race engines with street headers or some squid on the street with a stock engine and short race pipes. Get all the pieces right and they don't add up, they multiply!
I started noticing the factory honda DOHC 750's had the same radical cam sound,.. like they stuttered a bit through the revs and then cleaned out and pulled like crazy. They also ran header primaries much shorter than stock and short intakes. The cb550 Yosh race pipes had short primaries as well. Mine was made by Yoshima but appeared to be a copy.
I originally had 4 petal reed valves fitted to the heads (that was not a misprint) the experiment was to retard the cam to have a very late closing intake, and let the reeds determine actual intake closing based on flow reversal. It ran a whole season that way until some epoxy filler I used in the reed bodies started to loosen. Since I had the slotted cam gear I continued to experiment with cam timing after I removed the reeds.
The reeds were amazing, it was an attempt to have pseudo variable valve timing and it worked well. Despite the radical cam and retarded timing it had a meaty midrange and great top end. just felt like a 750!! I did a patent search and found it had been done before on four strokes but for very different reasons, mostly to prevent backfires on big singles and once on a car but looking for fuel efficiency instead of performance.
At that point I was starting to do well on the track and added the CR gearbox. I reasoned that it would be best to sacrifice midrange and lose the restriction that reeds must surely have on airflow. Once the epoxy came loose I removed the reeds and the bike became very cammy feeling. Incidently, the reeds didn't seem to hurt the top end much just going by feel but they sure did fill out the midrange.
After the 650 came out I compared heads and the stock 650 looked WAY better than the Yosh ported head. I was done racing by then but always wondered what that could have done for me. I remembered Yosh advertising 75 HP was possible? Presumably that was with their 590 kit, TT cam, race pipe and CR31's?? I ran VM29's and liked to think I must be around 65-70hp but who really knows? Four seasons, stock rods and total reliability except for that time I missed a shift at 10K and floated the valves!! bye,bye nice ported head
Just for comparison I could outrun any RD400, GPZ550, 500 and 750 interceptor. About tied or slightly slower than the last GPZ750's. I ran C superbike, B superbike and formula 2 and trophied in all of them. The chassis used a bimota style single shock, single front rotor with two calipers and anti dive linkage. Dymags, and a pro squat linkage on the rear brake. Gotta dig out some old pictures...
I keep hoping someone else will try the same cam/pipes/intake length/carb size combo I had to see if it was just a fluke?? Brent, you have the gearbox, I hope you'll shorten your pipes and intake manifolds? Should be able to scrounge up a TT cam too? I still have the pipes if you need measurements.
