damaged from the engine being run low
on oil. Since a full-engine rebuild was
needed, we treated it to a fresh top
end with Hot Cams high-performance
cams; a 478cc, big-bore cylinder; a
piston kit from Cylinder Works; and
a new crankshaft assembly from Hot
Rods. The high-performance parts
were actually less expensive than
stock parts. For example, the stock
crank assembly costs $404. The Hot
Rods crank is only $260.99! Yamaha
doesn’t offer a complete top-end kit
like Cylinder Works, but the original
piston and cylinder cost more than the
Cylinder Works kit, which also includes
the piston rings and top-end gaskets.
The Stage 1 Hot Cams we used for the
Yamaha use the stock valve springs.
ParaPros assembled the engine and
jetted the stock carb to work with the
engine mods and performance exhaust.
To protect the new engine and
provide unrestricted intake, we installed
a Uni Filter. FMF’s Powercore 4 titanium
exhaust saves weight and lets the
cammed, big-bore YFZ engine breathe.
A Hinson clutch makes sure all the
modified engine’s extra power reaches
the rear wheels.
With fresh suspension and the engine
running better than new, the YFZ
wasn’t just fun to ride, it could perform
like a competitive race machine again.
All it needed to be ready and reliable
for racing were new tires and wheels
from STI, pegs and nerfs from Tusk,
new graphics, and a new chain and
sprocket set from Renthal. Everything
that we needed for the Yamaha,
including the engine parts, was
available from Rocky Mountain Cycle.
The big-bore kit bumps the YFZ450’s displacement to 478cc. It comes
with a new cylinder and matched piston so there are no machine-shop
costs. Hot Cams Stage 1 cams use the stock valve springs.
The Uni dual-stage air filter filters even fine dirt efficiently, and flows
better than the stock filter.
ON THE GAS
Our project YFZ soundly outpowers
and outhandles the impressive first-generation Yamaha it’s based on. The
big-bore engine pulls harder at lower
revs than the stock engine, and the
modified engine’s advantage grows
as the revs build. Having more low-end and midrange power makes the
modified Yamaha quicker and easier to
ride, and the top-end pull is amazing.
This machine would work well for
cross-country or motocross racing, and
it’s a powerful, reliable setup for playing
in the dunes too. Your old YFZ may not
have the excellent Elka front shocks
our test riders did, but Race Tech can
rebuild and re-valve the stock shocks
from most sport quads so they perform
better than new. ❏