i do not believe that adding pipes or different jets can change "compression ratio". Which is just a ratio of the engines 2 volumes BDC and TDC
What i think they are trying to say is that by adding pipes and or larger jets, you can increase the "pressure" in your cylinders. The volume of your BDC and TDC are still the same, but now you are sucking in more fuel/air for each stroke. So when your piston moves from BDC to TDC, there is more substance (fuel) in it to compress. Just imagine a cylinder full of water. there would be so much pressure in it that it wold not turn over.
Increased pressure causes increased heat. Thats why turbos use intercoolers to cool down the compressed charge flowing into the engine. So increased heat might now call for different heat range plugs, different air screw settings etc.. So then you have to start retuning. And then after you have retuned, you have made changes, and you could probably retune a bit more.. etc... each time you are theoreticaly getting closer to the best performance. But the closer you are to the perfect tune, the closer you are to failure! So Be Carefull
on some bikes, jetting down with pipes might end up happening. Other times you might just stay stock. These can both be due to the fact that your new pipes do not restrict the motor as much and allow more air flow though your engine. This in turn pulls more fuel through your stock jet.
However it is very unlikely that you will get so lucky.
This is why it is best to jet rich with a new pipe and work your way down.
its a Pain in the ass to buy the jets, plugs, and keep pulling the tank airbox etc and keep testing
But, as you can see from the recent topics of melted pistons, its not such a PITA after all..
I do not claim to be a jetting guru
so its possilbe everything i just wrote is inaccurate
Im sure others on this site can add more information
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Koren
2 Strokes and I'm Off
