2 stroke timing

[russ jensen]

majority of 2 strokes I have checked have 18 deg advance and avg 4 stroke run in the neighborhood of 36. Why??? I have asked some pretty sharp design engineers and they never could explain why.`````

[1212FBGS]

compression and port timing.
 2 strokes run far lower primary and secondary compression (7 or 8 to1 on the 2 stroke vs 10 to 17 to 1 on the 4 stroke.) Also the exhaust port may still be open at 30 degrees depending on the engine tuning design.
kr

[Nortonist 592]

As two stroke ports are in the barrel the timing is symmetric.  That is, the exhaust port opens and closes at the same point atdc and btdc.  Exhaust ports usually open and close at 90 degs.  Because the expansion chamber plays such a big part in the power making part of a two stroke the ignition does'nt need to be too far advanced.  Don't ask me to explain that part.  I'm very fuzzy on it.

[Kato Engineering]

the blow down rate can allow a different amount of effective spark timing along with the new breed of power valves on the exhaust port to change what the static requirements of the tuned pipe are able to conform to.

we have alterd  the spark timing....

[russ jensen]

On opposed piston 2 strk  there will be no  expn cmbr & port tmg isn't symetrical either, looks like will have to time like Jack D : twist dist till fire stays inside& hope pistons don"t melt till it's right.