Crossflow Engine Tuning

[doppler491]

Can anybody share some insight into successful porting ideas for crossflow engines? For a single-cylinder motor with a single exhaust, intake, and transfer port (a motor with no reeds) where would the ideal location of the intake be? - I've got two cylinders; one with the intake under the exhaust and another in between the exhaust and transfer... And can anybody recommend a tried and tested exhaust port shape for cross-scavenged motors?

[Mark75H]

Cross flow motors are built the way they are for ease of manufacture and good mid and low range power. Reed valves generally add to the same part of the power band.

It doesn't really matter where the piston port intake is, but on your second motor ... it sounds pretty crude. To get any high output, you need more transfer ports, esp with piston port intake.

The most successful modified exhaust port shape for deflector motors is to square the top of the port so more window is open sooner (without raising the port). If the port does not have bridges you have to be careful it is not too wide or the ring will drop into the port.

[doppler491]

The cylinder with the intake below the exhaust port has a bridged exhaust... Are you essentially saying a flat topped, but wide exhaust port is what I should look at achieving? I'll try to post up a port map of what I have so you guys can have a look and try to help - I'm not working with much motor so I doubt there's much that can be done. The engine runs at about 5,500rpm max and turns a 7 1/2 x 7" prop...