TECH TORQ
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fun. A mate with some
smarts regarding Harleys
reckons the Sportster is a
better engine than a Big
Twin to play with. Whattaya
reckon?
- Harro
Well, yes Harro in many respects
it is. For one thing the engine
pushrods are on the same plane.
The Big Twin engines use offset,
or angled, pushrods to handle
the valve operation where the
Sportster’s are straight, which is
more efficient.
The Evolution Sportster
engine was released way back
in 1986, which is before many
of our readers were even born!
But that’s partly why they are
so good. Due to years and years
of continued improvement
and updates to that platform, it
has become arguably the most
reliable engine produced by The
Motor Company. You can see an
outline of the valve train geom-
etry in the illustration above.SPORTSTER
POTENTIAL
Doc, a mate of mine is think-
ing of hotting up his Sporty.When I said, ‘Buy a real bike’
he got a bit dark. More than
a bit, actually. But if you got
really serious what sort of
numbers could be achieved
with a Sportster engine?- Dan
Dan, a few years back Mark
Hood of Hood Engine Service
in Adelaide, who is a recognised
guru of high performance
engine building and no stran-
ger to these pages, decided he
wanted to build a fast and very
powerful Sportster as a kind of
in-house project.
Technical specifications of
the engine included a bore and
stroke of four inches, a 100
cubic inch capacity, running an
11.6:1 compression ratio, with
V83 Andrews cams, STD heads,
S&S cylinders and crankcases,
a 45mm Mikuni, a close ratio
Andrews transmission and an
Alto clutch with Barnett spring.
Steve Townsend of Steve’s
Cycle Fabrications modified
the frame for Hoody and built
the exhaust and also did the
required frame mods, with
the donor bike being a 1996
Sportster Sport.
Dyno testing brought in