He can quantitate all he likes, however, JUST the compression isn't the only thing that changes when installing a pop-up piston, the flow characteristics of the upper transfers are also altered, changing the efficiency of the loop scavenging effect. Mostly in the primary clearing of spent gasses from the top of the piston. It doesn't take a big imagination to imagine this especially after seeing wash patterns pop-ups create or the power created that never impressed me and is why I don't mess with them, as flat tops so better(here's your sign)
If you're going to make a decision about compression a better test should be devised, that's all I'm saying here, then going from a flat top to a pop-up, there's more going on than reading a gauge.
My thoughts lean to cutting the top off the cylinder and making a separate head that could have the combustion chamber turned down in stages and ran between those stages to really see what is happening and what's going on with just compression and compression alone, thus eliminating any other changes that go along with piston or cylinder alterations.
A simpler test could be possible with using one ring and grinding it down to increase the end gap to relieve compression.
Then again, having changed out countless worn-out sets of rings producing low compression, replacing them with new ring sets has always resulted in a better running saw.
Now someone is going to chime in and say, hey Stump Shot, race saws don't have high compression and look how fast they go. True. No load or low load speed can be increased with low compression. I started up and old completely worn out saw with no compression(took a bit of coaxing to start it) and it screamed until it quit making noise before I could shut it down. If a hair would have hit the chain that would have probably stopped it. Most race saws get by from being very large and the load applied fairly small. Increase the load and the cut speed will reduce dramatically.
Now that I've nearly written a book, do I believe super duper ultra high compression is everything, No I don't. Do I believe a bump in compression from stock is helpful, yes I do. Do I believe there is one number in PSI that is key to making power, no I do not, as engine sizes change as well as bore and stroke combinations, it's a variable number at best. Do I think it's interesting and even fun to mechanic on saws and find out for myself how things change from making alterations to the running components of the saw, absolutely. Do I have some ideas of what makes things tick, I'd hope after all the testing I've done over the years has learned me the tools of knowledge to allow me to work. What I really think the most is if you want to know something bad enough, try it out for yourself, then you'll really know something of use and can transpolate to the work you're doing rather than rely on someone else's efforts that may be different than your own for any number of reasons.
Carry on...
