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| Honda
TRX 700XX IRS Sport ATV |
With the introduction of the all-new
2008 TRX700XX, Honda enters the large-displacement
Sport ATV market at the peak of the
high-performance curve and accelerates
into the red zone where no one can
follow. Its electric-start, fuel-injected
686cc four-stroke engine traces its
heritage to the Baja-dominating XR650R
and delivers class-leading power.
Just as significant, the drivetrain
and suspension of the TRX700XX are
state-of-the-art—and then some.
Specifically, Honda has engineered
a brilliant centered chain drive system
that permits the use of fully Independent
Rear Suspension (IRS) with more advantages
than traditional IRS designs.
2008
Honda Sport ATV Models
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The adult Sport ATV market in the
U.S. continues to mature and today
can be classified in three distinct,
yet overlapping segments. The first
is occupied with 250-400cc models
that provide lightweight, tractable
power and convenience of operation.
The TRX250EX, with its innovative
SportClutch, and the ubiquitous TRX300EX
are wonderful examples of this category.
On the other end of the spectrum are
focused, competition-oriented machines
like Honda's TRX450R, which boasts
a ready-to-race liquid-cooled, four-valve
Unicam™ four-stroke engine and
agile suspension. Straddling the line
between entry level and pure competition
machines are the high-performance
sport ATVs that add season-long capability
and versatility to the high-performance
formula. The TRX400EX, with its bulletproof
XR400-derived air/oil-cooled four-stroke
powerplant and cast-aluminum swingarm,
slots in well here. In keeping with
the increasing expectations of riders
in this segment, the new TRX700XX
carves out new ground at the pinnacle
of the Sport ATV market.
TRX
700XX Engine / Drivetrain |
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Honda
TRX 700XX 686cc dry-sump,
liquid cooled SOHC four-valve
single-cylinder four-stroke
engine |
The lifeblood of the 700XX is its
686cc dry-sump, liquid-cooled SOHC
four-valve single-cylinder four-stroke
engine. With a bore and stroke of
102mm x 84mm, it boasts the largest
diameter single-cylinder that Honda
has ever mass-produced. Although it
is infused with the heart of the potent
XR650R mill, the 700XX engine has
been purpose-designed and built for
the rigors of ATV duty. Given the
higher weight of ATVs (compared to
off-road motorcycles), torque—and
lots of it—was a priority. A
longer (plus 2.0mm) stroke and slightly
larger (plus 1.4mm) bore accomplish
this. But in keeping with Honda's
philosophy of mass-centralization
and a low Cg (center of gravity) to
achieve optimal handling, engineers
determined that a taller cylinder
and engine would not do. So they shortened
the overall height of the engine by
creating a longer-throw crankpin and
a correspondingly shorter, carburized
connecting rod to shorten cylinder
height. The connecting rod is affixed
to a ball-bearing crankshaft. Smooth,
all-day riding comfort was assured
with the fitment of a gear-driven
counterbalancer to neutralize engine
vibration.
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TRX
700XX Cylinder & Piston |
Like Honda's renowned CRF®
motocrossers, the XX piston features
a slipper skirt design and it strokes
through a centrifugally forged,
3.5mm-thick steel sleeve. A forged
piston was used to handle the increased
mechanical and thermal loads, and
it also benefits from an underside
shower of cooling oil shot from
a jet that protrudes into the center
of the engine case. Compression
is 10:1 and the high-tech slug is
fitted with a larger 24mm piston
pin. The combustion chamber utilizes
a pentroof shape and is fired by
a single, centered spark plug.
The engine inhales through a foam air filter
fitted in a 7.6-liter airbox. Intake valve size
is 1mm smaller than those used in the XR (36
vs 37) for better low-rpm flow—and therefore
torque—while the exhaust valve diameter
remains unchanged at 32mm. The Programmed Fuel
Injection (PGM-FI) system draws fuel from a
3.0-gallon blow-molded, multi-layer fuel tank
and delivers it via a single Denso injector
through a 44mm throttle body. A Keihin Engine
Control Module (ECM) manages both the fuel injection
and the transistorized ignition. The engine
exhales through a single long-tube header tuned
for excellent low-end and mid-range torque without
sacrificing top-end power. Gases are expelled
through a muffler constructed of 128-grade stainless
steel.
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| TRX
700XX large 7.6 liter air box with foam
air filter |
TRX
700XX 44mm Keihin PGM-FI System |
