Bryan:
I suspect you already know the answer to your question-- todays 1-liter
4-strokes are only a little faster (about 20 - 25% more powerful) than the
500cc 2-strokes that dominated MotoGP in 2002. Another way of saying that
is that the modern, hi-tech 2-stroke is about 1.7X as powerful (per cc) as a
comparable 4-stroke-- that's why they interest me, also! (BTW-- the MotoGP
2-strokes produced up to 6.5HP per cubic inch!!!)
(If anybody knows where I can get one of those surplus MotoGP 2-strokes--
please contact me off-list!!!)
I think you are probably right about what is limiting the power of the
outboards-- non-use of expansion chambers (won't they even let them use them
in racing??), and (comparitively) low RPM. There may be other reasons that
we haven't figured-out.
As you imply-- it's no huge expense to sticking good expansion chambers on--
even if you need 6 of them.
On the other hand-- an engine that is built to run 7500 RPM will likely
destroy itself before it reaches 13,500 (where the 2-stroke MotoGPs were
running). I think you'd need to do quite a bit of internal build-up to get
it to stay together at RPMs where it would be competitive with the 4-stroke
bike engines (which run in those same RPM ranges, stock). Also-- the power
improvement from increased RPM could not be maximized without re-timing the
intake and exhaust ports, which requires considerable expertise (like
designing cams).
One last rap against the outboards, and then I'll shut-up: In the seventies
I was lab leader on an EPA "off-road sources" project at Southwest Research
Institute. The project included several outboards, of various sizes. I had
to set them-up and run them on the dyno (no, Joe-- NOT a chassis dyno). I
had a HUGE problem getting the outboard drivetrains to stay together long
enough to finish the test series on each engine. Running props in water, I
guess they just don't need to design-in much torsional strength. At any
rate-- if I were going to do a lsr outboard, I wouldn't use any outboard
powertrain part past the crankshaft (on a bike or a car)-- and I'd be always
worried about breaking the nose (drive hub) off the crank.
I would be very interested in seeing someone do a lsr outboard, and I agree
that there appears to be a fair possibility of a good result. However,
using 4-stroke sportbike engines seems a much shorter path to success, to
me.
Russ, #1226B
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