Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126605
The Champion Moriwaki GPz doesn't look radically different than stock. A quartet of Keihin CR 26mm smoothbores let the motor breathe deeply, Externally. the biggest difference in the engine appears to be pipes, carbs and a different case cover. Internal changes add lots more punch. Despite the large aluminum silencer. the engine is too loud for street use. The reservoir for the shock more tha n doubles its oil capacity, Champion Moriwaki Kawasaki GPz550: 11 sec., 130 + mph middleweight By Pa t Eaga n Because of the econom y, p eople are buying smaller displacement m otorcycles than they were a few years ago. But, until the introduction of- the Kawasaki GPz550, the sporting enthusiast had no option in the mid-displacement category. Now, . d h thanks to Kawasaki an Yama a with their Seca and Vision, the 30 performance nut can have his cake and afford it , too . One area where the rider who is downsizing from 1000cc would have to make an adjustment is acceleration and top speed. Either he'll have to accept less, or he can spend more money to get engine performance like he's used to . With the complete Moriwaki package as tested on a GPz550, the average rider can expect to tum the quarter mile in the high lIs at ab~ut 110 miles per hou r. If your name 15 Pee ~ee •.you. can go 11.75 a t 112 mph. This bike IS as fast as the modified Suzuki which won the 750cc class at the 1981 AFM Six-Hour. The heart of this little stormer is the 595cc Moriwaki piston kit . It features light pressure-cast pistons which are 2rnrn larger than stock at 60mm bore size. The 10.5 :1 compression ratio pis tons use a single Dykes-type compression ring for superior sealing and reduced fric tion. The cross section of a Dykes ring looks like an L . Combustion pressure is supposed to get in behind the ring and force its face out against the cylinder wall . Because only on e rin g is used , th ere would be less friction compared to a two -ring piston. The kit as sold incl udes pis tons , rings, pins and clips , and a head and base gasket. If the piston kit is the heart , then the cylind er head is indeed the brain. The motor in this '82 GPz550 uses a com plete head assembly as modified at Moriwaki 's race shop in Suzuka City . Japan. Moriwaki starts with a brand new head a nd ports it to his specifications using 1mm oversize intake valves and standard size exha ust valves . Both valves are shaped and polished to im prove flow characteristics. Part of the job is to shim the valve spring seats to achieve proper valve spring installed heights. Moriwaki manufactures his own racing valve buckets which are a different material and lighter than the stock components. The surface that the cam rides on is hardened to be compatible with the Moriwaki carns. This motor uses the Moriwaki Superbike Race Carns which open and close at 25"-55",