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Fraternal Twins
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Graves Motorsports Yamaha R6
Barry Winfield
07/01/2006
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Photography by Scott Gilbert
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In the stillness of a high desert afternoon, we can hear the 2006
Yamaha YZF-R6 clearly as it makes a test run toward us. Considering the bike is
still at some distance, the high-pitched wail cuts through the air with amazing
clarity, and the gearshifts come in quick succession as the 599cc engine rips
through the top end of its rev range in each gear. Close-ratio transmissions
make that possible, and they are invariably fitted to high-revving engines,
where the power band is comparatively narrow and crowded into the top end of the
engine’s usable rev range. In this way all ultra-high-performance engines
are related, because the principles observed in the design and development of
high-output engines are essentially the same everywhere.
Because all engines
have numerically equal torque and power values at 5,252 rpm, by definition, the
only way to extend the horsepower of a particular engine is to raise its rate of
work by increasing the speed at which it operates. Loosely speaking, torque
multiplied by revs (divided by 5,252) equals horsepower. That’s why, when we saw
early versions of Yamaha’s R6 at the big motorcycle shows that preview each
year’s new models, the big shock was a tachometer with a 17,500 rpm redline. Was
it possible, we wondered, for Yamaha to have produced a production engine for a
street-legal motorcycle with rotational speeds in the rocket-science realm of
Formula 1?
 It didn’t take long for the answer. No, Yamaha had exploited a
fairly typical nine-percent tachometer over-read inaccuracy for its shock value
in this innovation-driven motorcycle market segment. Aftermarket tuners, working
with sophisticated electronic dynamometers, soon discovered that the bike’s
ignition-control module limits engine speed on the R6 to about 16,000 rpm.
That’s pretty high, but it isn’t much higher than what other 600cc supersport
manufacturers currently use. Suzuki’s GSX-R600, for one, wears an honest
16,000-rpm tachometer redline. (Click image to enlarge)
Still, the Yamaha engine makes extraordinary
power for such a modest displacement, generating 131-horsepower at 14,500 rpm,
according to Yamaha’s publicity materials. Moreover, dyno tests show that it
continues to make significant power well beyond the 14,500 rpm power peak. That
calculates to a specific output of 220 hp per liter. Remember, it wasn’t so long
ago that 100-horsepower-per-liter was considered pretty good in a normally
aspirated engine.
 Currently in F/1, specific output beyond 300 hp/liter is
the norm. This is accomplished with engines that are required to fulfill two
weekends’ of testing, qualifying and racing—no mean feat given the technological
ragged edge on which these engines live, but still a far cry from the role
expected of Yamaha’s little 600. That engine must meet international emissions
and noise regulations, start and run reliably every day without external
starters and laptop supervision, meet stringent warranty requirements, and
provide civilized drivability and good fuel consumption. (Click image to enlarge)
Admittedly, some of
those challenges take a backseat on the Graves Motorsports Yamaha R6 seen on
these pages. Despite competing in a Supersport formula heavily based on
production machinery, with modifications severely limited in scope and
magnitude, the R6 is allowed less restrictive induction and exhaust flow, along
with whatever fuel injection and ignition mapping changes the tuner considers
helpful.
It’s increasingly clear that today’s 600cc sport motorcycles are
developed with a view to racing in the AMA national series as well as in the FIM
World Supersport championship. Much of the technology employed is the same as in
any prototype racing engine. Straight-shot ports conduct the fuel/air charge
directly into the cylinders. Four valves optimize gas flow into and out of the
cylinders, and they’re made as large as the bore size will allow. The cylinder
head design is painstakingly shaped to promote fast and complete combustion,
with a high compression ratio for optimal gas expansion rates. The engine
geometry embraces a radically over-square design (where the stroke is short
relative to the bore), and the pistons are lightweight units with minimal skirts
and relatively thin, low-friction rings. Special vents between the crankcase
compartments reduce pumping losses at high revs.
 Suspension performance is crucial to the success of the Graves Motorsports
R6 on the race track. Data acquisition from the Öhlins. (Click image to enlarge)
The R6 uses linerless
cylinders with ceramic-composite coatings to keep block weight down, and it is
exactly this kind of exotic technology that was pioneered by Formula 1 teams.
For example, Mercedes F/1 engine suppliers Ilmor Engineering developed the use
of beryllium-aluminum piston materials in the late ’90s, but when this material
was outlawed because of possible health hazards, the GP circus moved onto
so-called metal-matrix composites deployed in linerless cylinders in much the
same way as on the R6. Other lightweight materials are exploited in both
disciplines, with titanium and magnesium castings used wherever they can pare
off a few ounces. The R6 uses a titanium exhaust system, while F/1 cars go for
thin wall Inconel tubing. Advanced metallurgy is common to car and bike engine
design, finding applications in low-friction bearing material as well as in
low-weight casings and componentry.
 Computer science joins physics as lead players in the success of
today’s high-performance competition machines. (Click image to enlarge)
As engine speeds rise, friction becomes
a greater factor. Some internal losses quadruple as engine speeds double. At
least a few motorcycle racing teams have discovered that ongoing development
produced higher engine speeds, but the resultant increases in power have been
eaten by increased friction. One answer has been to reduce bearing area to the
very minimum, but that’s a technique fraught with risk. Bearing failure ends
your race, and it isn’t good business on the consumer side either. Bearing life
can be greatly extended with good design, and that’s where the computer often
comes to the rescue. Modern design and simulation software helps produce engines
that are stiff and strong, resisting the bending and flexing that occur at very
high operating speeds. Maintaining exact alignment is key to bearing life, and a
close look at both F/1 and high-output motorcycle engines quickly reveals the
lengths to which designers have gone to embrace maximum structural integrity.
The castings are replete with webs and gussets, and crankshafts are mounted in
heavily reinforced bearing ladders.
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