The KFX450R’s power plant, based on the highly
acclaimed engine of the KX450F motocrosser, was newly
designed for use in an ATV racer. Adding fuel injection,
an electric starter, fitting a reverse gear, lowering
the centre of gravity by tilting the cylinder bank
angle forward, re-tuning the engine for low-mid range
torque to suit the weight of an ATV, and revising
the intake and exhaust systems are among the many
changes.
The KFX450R’s
power plant, based on the highly acclaimed
engine of the KX450F motocrosser, was
newly designed for use in an ATV racer.
The camshaft
lobes and tappet surfaces feature a
soft-nitriding surface treatment for
long wear and high-rpm reliability.
The compact
reverse-lock release lever prevents
accidental selection of reverse. Simply
push the lock lever with your right
thumb, then click down the foot shifter
from first to reverse.
Lightweight,
high-performance titanium valves ensure
accurate valve timing even at maximum
engine speed. Oxide membrane treatment
resists wear.
A lightweight forged piston reduces reciprocating
weight.
Triple piston rings and a 21 mm diameter piston
pin help increase durability and reduce necessary
maintenance.
Improved low and mid-range power characteristics
for gutsy response when climbing hills, riding in
the mud or in other poor-traction, low-speed conditions.
Lightweight high-performance titanium exhaust header
pipe contributes to low-mid response.
A large-volume airbox contributes to both intake
efficiency and the sharp engine response. An air duct
fashioned from polyethylene (known for its ability
to resist deformation caused by intake pulses) helps
ensure stable engine performance.
Efforts were made to achieve the widest possible
torque band, so that traction efficiency would be
maximized for a greater part of the rev range.
The KFX450R’s linear power curve features
plenty of over-rev, giving riders ample latitude in
choosing their shift intervals.
Digital Fuel injection. With carburetted engines,
race set-up is often a question of compromises, choosing
the best overall settings. Fuel injection increases
race competitiveness by eliminating a key disadvantage
of carburettors. When racing in highly variable conditions
(such as in the hills or the woods, where air pressure
and temperature can vary greatly) fixed carburetor
settings may not always be ideal for the conditions
at hand. The adaptability of fuel injection means
riders no longer have to make compromises when it
comes to engine settings.
Taking into account water temperature, air intake
temperature, throttle position, air intake pressure
and engine speed, the fuel injection system automatically
meters out the ideal amount of fuel for extremely
stable power deliver – no matter what the conditions.
Large, single 42mm throttle body and 32-bit CPU
ensure high power output and precise fuel metering.
Engine response is sharp. This can be especially advantageous
for instant acceleration after landing jumps.
Fuel injection also ensures trouble-free starting
– a great benefit in races where riders line
up with their engines off and need to start their
engines before being able to blast away.
With fuel injection, throttle lever operation is
extremely light (unlike on FCR carburetor-equipped
machines), which helps reduce rider fatigue.
Standard equipment electric starter. With an easy
push of a button the ATV can be quickly restarted
– getting you back in the race sooner.
High-capacity starter motor is compact, yet high-output
ensures quick and reliable starts under all conditions.
The battery is located low and forward. Situated
in front of the engine between the lower frame rails,
the battery’s mass is ideally placed to keep
the ATV’s centre of gravity low.
An optional kick-start system is available for MX-style
(GNC) races where light weight is a priority.
Kick-starting a large-displacement 4-stroke engine
can be a lot of work, we want to make sure that the
engine starts on the first try, so we incorporate
the best automatic compression release (ACR) system
available. The dual-weight centrifugal decompression
system fitted to exhaust cam eases starting.
Five-speed transmission with reverse. When problems
arise, the reverse gear (another class first) will
prove indispensable in returning to the race quickly.
First-corner pile-ups are far from rare – the
ability to extricate yourself from such “traffic
jams” without having to dismount will save valuable
time. Passing slower machines in forest sections often
requires riders to leave the marked course –
knowing you can easily back out of trouble should
you make a mistake will give you the confidence to
go “off the beaten path” when necessary.
The compact reverse-lock release lever prevents
accidental selection of reverse. Simply push the lock
lever with your right thumb, then click down the foot
shifter from first to reverse.
The 5-speed (1 down, 4 up) transmission locates
the reverse gear below first.
Selecting reverse is fast and easy. Actuating the
reverse-lock release lever when in 1st gear allows
you to shift “down” into reverse. To select
first gear from reverse simply lift up on the shifter.
Lock lever operation is by right thumb giving the
rider freedom of holding the front brake on hills
if necessary.
The combination of the reverse gear system with
the lightweight aluminium chassis is no heavier than
using a steel frame.
Lightweight, high-performance titanium valves ensure
accurate valve timing even at maximum engine speed.
Oxide membrane treatment resists wear.
Aluminum valve spring retainers reduce reciprocating
weight for reliable valve control at high-rpm.
Double valve springs also help ensure stable valve
operation and allow a short cylinder head height.
Revised cam lift and timing boost low- and mid-range
torque.
The camshaft lobes and tappet surfaces feature a
soft-nitriding surface treatment for long wear and
high-rpm reliability.
New rear shock features 5-way spring preload and
stepless rebound damping adjustability.
The new rear shock is complemented by redesigned
linkage for the rear suspension.
