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A Better Sportmaster?
Modifying a Mercury
Sportmaster
Article by Greg Terzian and Helmut
Freitag
Gaining
more top speed seems to be the never ending uphill battle for the
performance boater. It seems that our breed will do almost anything to gain
that extra edge. It’s not always about the speed gained itself, but rather
the challenge of unlocking all of the performance potential of our rigs.
One topic that is always the subject of debate and examination is the lower
unit of the outboard. That makes sense, as this is the part of the boat that
creates the greatest amount of drag, and therefore, creating efficiency here
can hypothetically reward us with significant gains in top speed.
We must remember that the lower unit is a design in compromise. The unit itself
must be large enough to encase the drive gears and bearings, while
maintaining the strength required for surfacing applications. Many
performance boaters and racers have extolled the virtues of modifying the
stock XR-series Mercury V6 cases because of their hydrodynamically-friendly small diameter
gear housing. The
addition of a nosecone and torque tab allows these cases to be the fastest
lower units short of a Speedmaster. The other side of the coin, however, is
that the XR-series and other stock V6 lower units are not designed for the
added horsepower and bearing loads of surfacing applications, and as a
result, are not durable. Yes, there are aftermarket bearing carriers and
modifications that are available to take up the slack in these areas,
however, these solutions are not always practical for the everyday
performance boater.
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Test
Boat:
1998 STV Euroski/Mercury 2.5 260 EFI |
One other point that
must be stressed is the strength of the skeg on stock lower units verses
performance units. Stock lower units are not designed for the side loads of
torque tabs, which must be installed for safety on single-engine
applications. A skeg fracture during a high speed run could initiate drastic
and unfortunate results – this is not a subject to be taken lightly.
Many quarter-mile racers have realized that a modified stock lower unit is
adequate for quick runs down the liquid quarter mile. There is a risk of
failure, however, it is not as great as it would be in sustained high-speed
runs. Also, racers are equipped with required safety equipment, which could
offer some insurance in the event of a lower unit failure.
The Mercury Sportmaster presented a perceived improvement over the previous
offering, the CLE (Crescent Leading Edge) lower unit. The Sportmaster is
Mercury’s performance offering, designed to be durable while handling high
speed, high load applications.
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Left: Factory
stock Sportmaster
Right: Fully modified Sportmaster |
The
Sportmaster featured a long bullet to help offset premature blowout, as well
as a blowout ring cast into the surface. It also featured a long, thick
skeg with a cast-in torque tab. The Sportmaster is large – some feel, too
large to be a capable performer verses other solutions.
Many
people started modifying this design, thinking there were speed gains to be
had from sweeping the skeg back, thinning it, flaring the torque tab in, and
in some cases, shortening the skeg. The theory is, less metal in the water
means less resistance, which equals more speed. We have seen references to
the “Allison cut” skeg – a cut on the Sportmaster skeg mimicking the
silhouette of a stock lower unit skeg.
We decided to put this
school of thought to the test, pitting a factory stock Sportmaster against a
fully modified Sportmaster. It must be stressed that Mercury Marine advises
against this sort of modification because of compromises in the integrity of
the casing’s strength. I would agree that this modification should not be
performed by the average person, and that there are increased chances of
lower unit failure as a result of these modifications. That said, let’s
move on…
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Article Information |
| We test a
modified Mercury Sportmaster lower unit to see what, if any
performance will result. |
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Created: |
| October 15,
2002 |
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By: |
| Greg Terzian |
| Helmut Freitag |
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Category: |
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Product Evaluations |
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