Job number one on any bike with a 1.1 kg/cm2 radiator cap is to replace it with a
high-pressure cap. This CV4 cap is 2.0 kg/cm2.
The Boyesen Supercooler water pump not only flows more water, but it lessens
cavitation to reduce the amount of air bubbles in the water.
We added a DR.D slip-on exhaust to help clean up the low-to-mid transition.
be set from 142mm to 146mm long
(when the JGR team raced YZ450Fs,
they ran the links at 144mm). The
longer links lowered the rear end from
8mm to 14mm to 19mm to 23mm,
depending on where we set it. This
allowed us to lower the overall frame
height by sliding the forks up in the
clamps. Plus, with a lower rear end,
we had more range in changing the
head angle with fork-height settings.
For summer racing, we wanted
our YZ450F to run cooler. We believe
that Cycra’s PowerFlow plastic not
only makes the YZ450F narrower but
allows more air to reach the radiators. Unfortunately for us, the Cycra
radiator shrouds wouldn’t work with
our humpback Twin Air Power Flow
airbox cover. So, we added a Boyesen
Supercooler water-pump cover and
impeller. The Boyesen pump eliminates cavitation, which means more
water and fewer air bubbles in the
cooling system. As has become rote,
we drop-kicked the 1.1 kg/cm2 radiator cap ( 15. 6 psi) for a higher-pressure
2.0 kg/cm2 cap ( 25. 6 psi) from CV4
Products to raise the boiling point
of the antifreeze from 265 degrees
Fahrenheit to 278 degrees.
CYCRA POWERFLOW PLASTIC
Yamaha based the plastic of its All-
Japan National Championship works
YZ450F, which should be the 2018
production plastic, on the looks of
the Cycra PowerFlow YZ450F plastic.
The Cycra PowerFlow radiator wings
eliminate all of Yamaha’s duct work
and double-wall plumbing to produce
a sleeker, narrower and cleaner tank/
radiator interface. It is a clean design
and can be ordered with just the
radiator wings and airbox cover or as
a complete plastics kit. We could not
mate the Cycra radiator wings to our
humpbacked Twin Air airbox, but if
we could, we would.
HOPPED UP ON STEROIDS
We tested Pro Circuit, DR.D and
FMF exhaust pipes, and they all upped
the oomph, especially when combined
with better breathing, crisper mapping and dialed-in geometry. As a rule
of thumb, fuel-injected bikes thrive on
aftermarket exhaust systems. They
tend to increase over-rev while taming
the barky throttle response off-idle.
Surprisingly, there is a percentage of
MXA test riders who prefer to run
slip-on muffler systems instead of
full systems, and another group who
like the mellow power delivery of the
stock YZ450F system.