In my opinion, pretty good for an (essentially) low revving engine. (the amount depends on what coil/CDI you use.), but typically, the older stuff is either 8 or 12 degrees. My experience with non squish heads has been that, like Teezee says, non squish heads require less retard, but more so with a "squish" head the ignition map used needs to be very well controlled (to suit the pipe design as as well), whereas, the non "squish" head shows more "real world" gains using only very basic ignitions (early "twist and go" scooters are a good example) that have between 8 to 12 degrees retard from static. My opinion is that, in the case of a compromised set of available gear ratios (4 speed) this is not ideal. Sure, that "squish band" head will make more power, it just places that extra power in a narrower RPM range. in the same way that having large exhaust port duration will. Using a "squish band" head will typically give a "peakier" power delivery (although it will indeed give a higher "peak power" result). That is a really good idea Skunk (in my opinion).the TYPE (i.e useable spread) of power you are looking for on a 4 speed transmission is quite different to what you would be looking for with a close ratio (6 speed) (or,like Cagiva did with one of their Mito road 125's 7 speed!) gear box. I'm also researching doing away with squish. This gives the inlet a dwell period where the inlet is fully open for a time, the more the better he says. And he likes to strike a compromise with port height to width, so he can cut something off of the piston skirt so that the piston clears the top of the inlet port around TDC for 30-50 degrees or so.
![two stroke performance tuning two stroke performance tuning](http://www.hpracedevelopment.com/uploads/4/6/5/3/46537493/7910520_orig.jpg)
The inlet port needs to have much the same area as the carb. Interesting info about maintaining port velocity:. Thomas says a low wide port fills the crankcase better than a tall narrow one of the same area. This gives him an idea of how much he can cut off of the piston skirt and/or lower the inlet port floor. Thomas finds the inlet opening position then marks the piston skirt through the inlet port. Then he measured how much he had to raise the exhaust and lower the inlet. The thickness of the packing was the amount he had to take off the top of the barrel. I've yet to triple check my measurements.When Thomas set our engines up, he used a degree wheel, found TDC and then packed the cylinder up a bit at a time until the transfer ports opened at the required point.