QUOTE (7okai @ Apr 25 2011, 08:40)

Hi Giovanni,
I can help a little with the PRP 500, as I had a couple of rides on it back in 1991.
The name PRP comes from the Australian frame makers PR Products. The P is for "P"eter MacMillan and the R is for "R"on Taylor, these two gentleman started the business in the late 1970's and produced aftermarket chassis, mainly for TZ Yamahas. Later on, Peter Macmillan was joined in the business by his brother Graham Macmillan. Some time later, Peter moved on to pursue other interests, but has remained involved in the motorcycle world. The chassis were produced, in Sydney, at several premises that incresed in size over a period of time. Nowadays, Graham is still doing work for racers in Australia.
In 1971, my father built a 3 cylinder 525cc Yamaha from a 350 TR2 racer and this machine made its debut at the Easter Australian Grand Prix in 1972. The 3 cylinder idea had potential for good perormance. The principle was soon copied overseas using the later model TR3 engine, and these were more successful. Ron Taylor and Graham MacMillan produced a watercooled 3 cylinder version of this using TZ350A engine components and housed it in a purpose built steel tubed chassis. Ron competed with the bike with some success in Australia.
Later, after we had experimented with reversing the cylinder block on our 250 and 350 Yamaha TZ's, Graham developed a new set of crankcases and gearbox that used the advantages of the reverse cylinder application. A completely new chassis was manufactured in aluminium alloy. Although not a "Deltabox" design, the chassis was of the twin spar type and used a linkage rear susension system. The rear suspension unit was White Power and the front forks were Marzocchi. The 3 Mikuni 38mm powerjet carburettors were mounted in front of the engine. 2 of the exhaust pipes exited directly backwards, and were crossed over, in the style of the Honda RS500 under the seat cowling. The third exhaust pipe was routed to exit under the bike in the more traditional manner.
The bike was never tested on a dyno and estimates of around 100~110hp would be reasonable. One of the problems that the bike suffered from was the availability of a better ignition system than the standard Hitachi unit that was used. Also, because of this, it was difficult to adjust the carburettors to give the ideal throttle response and this always affected ultimate prformance in an adverse manner. The ultimate performance potential was never realised, yet even with the modest state of tune the performance was adequate.
My experience on the bike was in the middle of our winter, at Winton raceway. The temperature over the weekend was around 13~14C. This helped to mask the overly rich carburettor settings and the bike was running reasonably crisply. So much so, in fact, that the Clerk of the Course, Ray Le Nevez made the comment that it was the fastest that he had ever seen the bike at a race meeting. I must say that I thoroughly enjoyed my time in the saddle. A month or so later, at a much warmer but wet Eastern Creek meeting the bike was back in the hands of the regular rider Greg Drew. The weak ignition and the rich mixture made it almost impossible to start, and when it was running, it was much too rich.
The 2 riders that competed on the bike were Ron Sumskis and Greg Drew. Maybe somewhere, buried away in the archives, there are some pictures of the bike. If I find some, I will add them to the thread for you. I hope that this information is of some help to you Giovanni.
Hi, In the dim and distant past the Kawasaki works team were based adjacent to my mechanic training facility in Slough, 400 yards from the Deal Avenue HQ. Kork Ballington was the jock,with his brother Derek or "Dozy" usualy around. Stuart Shenton and Stewart Baldwin were engineers under that wonderful Japanese gentleman Ken Suzuki. The KR500 four was very quick but unreliable. I was trusted to keep quiet and picked up bits and pieces through just being around before and after GP's. Towards the end of its development the answer was available in computerised ignition with knock sensors that picked up detonation and backed off the timing so avioding overheating and internal damage. Unfortunatly it was too late for the project which was scrapped shortly after the answer was available. C'est la vie! I used to chuckle at the little notes the two Stewarts would write on gaffer tape stuck on the tank-for example "Here's a message from the lads-watch the brakes-new pads!" Happy days.