eliminating any hot spots, allowing for the use of a cast
iron sleeve. This reduces the need to use fuel as a coolant, resulting in improved
fuel economy. Ski-Doo claims that the type 583 required 400 grams of fuel per kilowatt
hour (think of this as "metric" fuel consumption; instead of pounds of fuel per
horsepower hour, the metric version is grams of fuel per kilowatt hour), and the
new type 593 only requires 330 grams of fuel per kilowatt hour, a 17.5% reduction
in fuel requirement.
The Elko pistons from Austria are a new lightweight cast
alloy with a single ring for less drag and efficient sealing, which should also
reduce hot spots and detonation problems. This piston is similar to what the 670
High Output engine uses with its flat top, which improves performance due to faster
flame propagation in the combustion chamber. The two-piece cylinder head features
hemispherical combustion chambers with wide squish bands, which were designed in
conjunction with the new flat top pistons.
The crankshaft is heavy-duty unit with 809 type big end
rod bearings, along with new nitrated steel cage ball bearings, including a
nitrated solid retaining pin. The mag end features a new style seal for greater
durability, while the PTO end has a 7.5:1 taper and a new fully oiled outer
bearing. This oil line also is routed to the center water pump gear for excellent
lubrication and durability.
Rich Daly at Dyno Port (315-258-5618) was able to obtain
one of the first MX Z 600s out of the factory and immediately placed it on his
Huff-Depac dyno. Ski-Doo personnel at the Snow Shoot in Quebec in March were
estimating 105-110 HP from this new engine, so our expectations were high. Much
to Rich's surprise, the new engine only produced slightly more than 101 HP. Ski-Doo
informed us that the 600 has an ignition feature that retards the ignition timing
by 3 degrees for the first four hours of operation beginning at 4,000 rpm,
after which
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the engine would make full power. After the four hour break-in period, the following dyno run was
recorded pulling 104.0 HP at 7800 rpm. The stock jetting was pretty lean compared
to typical fuel flow numbers, but Ski-Doo insists that this is normal for this
engine. Ski-Doo also told us that the pipe needed to be good and hot before it
would make full power, but Rich found over the course of four dyno runs that the
power did not increase appreciably with a hotter pipe.
Rich first built and tested a canister silencer, retaining
a larger volume for low frequency sound reduction as well as a dissipative glass
packing for high frequency attenuation. This silencer was 6 pounds lighter and
measured only 2dB louder than the very quiet stock muffler, and the following dyno
run was pulled, still using stock jetting. Note the similar fuel consumption numbers,
now producing 105.7 HP at 7800 rpm, with a slight increase in torque. Rich also noted
that the airflow had increased slightly by 4 pounds per hour. Rich made an attempt at
making more power by reducing the stinger outlet diameter
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of the stock pipe, but this
resulted in a loss of power!
Looking at the stock exhaust, Rich was concerned with the sharp
"U-shaped" return path of the exhaust coming out of the pipe into the silencer, and built
a single pipe that eliminated what he felt could be a restriction. The single pipes from
Ski-Doo on the 500, 583, 670, & 700 engines have been very excellent power makers and have
been very difficult to improve upon, but the 600 appears to be different. He was surprised
to see a significant power increase, and strongly suspects this is due to the sharp curve
at the tail section of the stock pipe.
The Dyno Port single pipe peaked at 111.7 HP at 8300 RPM, and produced a wide band of over
110 HP all the way from 8100 to 8400 rpm, with a torque peak of 71.8 foot pounds at 8100
rpm. With this pipe, the jetting was increased one size and the fuel consumption numbers
are slightly leaner. Rich did jet this set-up down one size and lost power, so ideally it
should be jetted up 1 more size to maintain the stock-like fuel consumption. This will be
two
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