On Thu, 18 Mar 2010 14:17:50 -0700, Jim Stewart
wrote:

Tim Wescott wrote:
Grider Pirate wrote:
On Mar 14, 11:30 pm, durabol wrote:
Thanks for the responses. I meant for ultralight or light aircraft
with 20-40hp from 1 or 2 cylinders. I definitely want to copy as much
as I can since I'm not engineer. I planned to have the RPM at about
4000 in order to get enough power out of the engine but I may reduce
the rpm if I can get enough power. Also I may have to weld the crank
together to handle the propeller loads.

Brock

'Restrictive' exhaust isn't a good way to avoid venting unburnt fuel,
and it will really clobber performance. If you're really trying to
get good performance, especially over a narrow band, then you really
need to consider using tuned pipes (AKA "Expansion Chambers"). Gordon
Jennings "Two Stroke Tuners Handbook" covers most everything you need
to design a two-stroke.
4000 RPM is pretty low for a two-stroke. The tuned length for the
pipe(s) would be around 6 FEET.

Ship's two-stroke diesel engines top out at less than 200RPM.

I don't think they use tuned pipes, but if they did I suppose they'd
have room.

Don't need them. They all have massive
blowers for scavenging.

I believe EMD built locomotive 2-strokes that
had a set of exhaust valves in the head and
a blower port that was opened at the bottom of
the stroke. No tuning, the blower was plenty
to force out the exhaust and fill the cylinder
with fresh air.
And at 200 RPM there is LOTS of time to purge and fill. Volumetric
efficiencies are pretty good.