Brian,


I would guess it has to do with what the user defines as a "definite four-cycle" and a "clean two-cycle".

No, I did not use the "charts" to estimate this .


Also, both engines that you mention are high performance engines; not the typical 'sport' engine.

When I began to break-in engines, as described in that thread, I took some tachometer readings, just out of curiosity and these were the typical RPM gains, when breaking into two-cycle (under my definition and hearing).

An engine doesn't double its HP, when going from four-cycle to two-cycle, probably because when four-cycling, the firing revolutions produce a higher-than-normal cylinder pressure. I am not sure about the reason for that.

And yes, with a tuned exhaust, looking for max RPM, an engine may gain as much as 2,000 RPM; more perhaps...


I credited you in the Diesel forum (the 'ether' thread).