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Thanks STIHL... about 2-stroke techniques in a 4 stroke engine.

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Lemans

Well-Known Member
Joined
Mar 23, 2008
Messages
599
Location
Toucy France
A few years back, I started rather enthusiastic my search on a 4-stroke +40 HP engine to replace my 503 Rotax.
Every engine I came across had his own inconveniences for my 'application'.

Industrial engines are simply not build to power part103 air-planes , nor are re-driven bike or auto conversions.
So, long time it looked impossible. Then I came across the lightweight 4-stroke lubrication solution designed by Stihl.

Not only was it possible to use their chainsaws in any possible position, they also manage to avoid excessive weight
by using needle bearings/premix instead of an oil reserve and oil pump.

As I am a fan of flat engines I knew the sometimes problematic pumping capabilities of any opposite 2-cylinder.
Every revolution they press their full displacement in and out the crank-case. Why not use this phenomena as a blower to gain a bit of power?
For this purpose I redrew the crank and connection-rods of a Citroen 2CV engine.
After that, I designed a sealed off crank-case just to find out the pressure that both pistons could deliver whiles moving towards each other.

Maximum volume (pistons in TDP) ;
1,880cc (blue volume) - 624cc (crank and conrods) = 1256cc

Minimum volume (pistons in ODP)
1256cc – 602cc (engine displacement) = 654cc

Theoretical absolute pressure available in the intake manifold (no transfer of heat) : 1,92 bar
Even with the inn-avoidable transfer of heat an absolute pressure of 1,5 bar must be possible.
This is encouraging, let's see what Lotus Software predicts for this tiny 600cc engine.....

Just my thoughts and maybe....to be continued.
 

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