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.
