by pacomotorstuff » Fri Sep 28, 2012 8:43 am
Brad,
I stand by my comments.
Yes, Yamaha built rotary valve road racers (RD56 for one) as well as their 125cc twin and later 4 cylinder 250cc race bikes. If any of them ever showed up at a VRRA grid, it would be amazing.
Yes, their (smaller cc) street bike line was rotary valve (50, 55, 60, 80, 100 and 125cc) all singles and all slopers. I believe all of them had cast iron cylinders though a few of the later ones - after '68 I believe - had aluminum cylinders with cast iron liners. Some of us will remember the GYT kits sold by Yamaha which made the 80's a real screamer but maybe a little small for P1-200 and would a GYT-kitted Yamaha be legal anyway?
I am not aware of Yamaha building a larger capacity rotary valve bike that was sold in Canada / North America and I don't think the 125 with its pressed steel frame, 4 speed transmission, 22mm carb and a stock weight the same as a Ducati 250 would make a very competitive P1 mount - but maybe I'm wrong.
Which leaves us with the original question posed - what would be the better platform to convert for P1-200, a CT-1 or a F7?
My response was use the F7 - rotary valve vs piston port was the main reason - more potential for horsepower. Stock factory ratings were 14HP for the CT and 21HP for the F7 (got these off the web today).
My other comments also hold true:
1) no Noguchi parts are allowed (for those of you who don't know, Noguchi was connected to Yamaha for a number of years as a Yamaha race development department), so no matter what you do to the little CT, not terribly quick and the Noguchi stuff when you can find it is pretty expensive anyway. You say the CT1 does "pretty good" down in the US -be interesting to see who uses what in their motors and if they would even be VRRA legal...?
2) if you can find an old Skunk Worx intake for the F7, it allows you to run something like a 32 or 34 mm carb and looking at the rule book, can't see why someone couldn't use one if they could find it or clone it if they had some good photos of one like I do (email me, Rick).
3) the F7 is a pretty modern motor for P1 IMHO. It was built from 1971 to 1975. I'm sure wiser heads than I knew what they were doing when the F7 was allowed in P1, but in 1967, the Kawasaki 175 F2 Standard was a 4 speed, cast iron cylinder, stamped steel frame and swing arm motorcycle which some of us old relics still remember as being sold as "The New K Bike!" by Canadian Tire. Dunno what parts are interchangeable, F1 vs F7 but my guess is "not many"...
4) looking for another chassis to slide either motor into. This is based on my own, personal "sad" experience of trying to get an enduro bike chassis to act like a road racer. Eventually, we went to a converted Yamaha street bike chassis - lower steering head position, shorter forks, correct steering geometry and enough info and parts out there to make chassis setup pretty straightforward. Pretty much how Kawasaki saw it when they started putting the Big Horn motor in the H1/H2 chassis I guess.
Anyway, my purpose wasn't to try to make grids smaller - in fact, just the opposite. I'm beating the bushes right now to find a P1-250 ride that I can afford - the BSA 250 I was looking at being wayyyyy out of my league, money-wise and a Triumph 250 I recently investigated, even more-so..
If you've seen Rick's other race bikes, you know he'll be gridding with a topnotch piece of equipment, the best, fastest and safest he can build and I say, "Bully for him", great to see another race bike on the grid...
Pat
Just look at those Harley racers 
