Cycle News

Cycle News 2022 Issue 40 October 4

Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles

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to the engine, giving him more clearance for the front wheel and thus making the front even more compact. The difference between the R1 powerplant and that of the ThunderAce was not just exter- nal size. Internally they may have shared the five-valve head, but the R1's inlet ports were smaller and inside the head sat smaller valves at a steeper angle, all in the name of increasing the gas flow. The blocks were different too, with the R1's bore and stroke measuring 74 x 58mm compared to the shorter stroke figures of 75.5 x 56mm for the ThunderAce. Below deck, the crankshaft came in for the weight-loss treatment. Yamaha engineers managed to shave an impressive 22 percent off the reciprocating mass of the crank, which was a major factor in the R1's impressive throttle pick- up. Swinging off the crank were new con-rods with lightweight forged aluminum pistons. Even though the two engines shared a claimed torque figure of 78 lb-ft, the R1, which carried an 11.8:1 compression ratio to the ThunderAce's 12.0:1, made that figure 1500 rpm lower at 8500 rpm. It also had an extra five horsepower, with a claimed 148 horsepower at 10,000 rpm. Those were serious figures for 1998. The Honda Fireblade, which for 1998 had grown to a 919cc engine, claimed power and torque figures of 130 horse- power at 10,500 rpm/67 lb-ft at 8500 rpm. And Kawasaki's ZX- 9R, which was also revised for the 1998 model year, produced 143 horsepower at 11,000 rpm and 74 lb-ft at 9000 rpm. These were still the days before fuel injection became commonplace in production sport bikes, and rather than get a jump on the pack by fitting EFI, Yamaha instead chose to fur- nish its new weapon with 40mm BDSR Mikuni carbs, which were 30mm narrower than the Thu- derAce's 38mm units. The R1 ran a throttle position sensor, which was also linked to the CDI unit, gear position indicator and the EXUP valve, and programmed to increase the available torque from 4-8000 rpm. Getting all that grunt to the tire was a new six-speed gear- box, replacing the five-speeder in the ThunderAce. This new gearbox became one of the few weak points in the 1998 R1's armor, but thankfully Yamaha CN III ARCHIVES P118 Red and White or Yamaha Blue were the only color options in 1998.

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