line pressure and so forth. But under
it all are the same basic principles.
Intake and exhaust modifications
have to work with ignition and fuel
mixture changes. The RZR we tested
was a Jagged X (the four-seat chassis
without the rear seats), and it had
a Duncan Fatboy exhaust and an
Advanced airbox. Side-by-sides are
further complicated because of the
importance of tire, wheel and clutch
modifications—all of which dramatically affect how the motor runs.
We’ve seen a number of RZRs with
engine modifications that performed
no better than stock. This wasn’t one
of them. Again, the Vortex CPU allows
you to make fine adjustments for fuel,
temperature and altitude. And as
with any emission-regulated vehicle,
the engine is screaming for more fuel
99 percent of the time.
Because of the RZR’s added complexity, the X10 designed for it sells for
more than the ATV version, at $799.
The versions for the Suzuki LTR450
and the Yamaha YFZ450 both sell for
$699. Considering the expertise that
goes into the manufacturing and programming, we’re amazed the price is
so cheap—little more than the cost of
a muffler. For more information, contact Duncan Racing at www.duncan
racing.com or (619) 258-6306. ❏
TURN BACK TO PAGE 18 TO
SUBCRIBE TO DIRT WHEELS