I agree with FUBAR'ing the ratio and flow that Honda has setup for sound and a few HP... But then again that never really crosses anyone's mind when they modify anything for that matter of fact.
The compression ratio is 10.7:1.
The pipe and breathing system is highly restrictive due to emission laws. Not to mention heavy. Freeing up the breathing system isn't modding the engine to extremes, it's simply allowing it to breath as it should.
Once this is done it's breathing a lot easier, but the stock CR will be messed up. The ECU will allow for some change but not much. Getting a new fuel map installed, or a powercommander/juicebox will sort this pretty easily. Hence the engine is running perfectly (as you wish as you're programming the compression ratio) and it's breathing freely without enforced restrictions.
It isn't changing the engine to perform beyond it's means, it's allowing the engine to run as it should without being choked up by emission laws.
Am not too sure why people need to say it's better to buy a 600cc than free up the 250cc engine to run as it should.
BTW, Honda made it very easy for a pipe change by placing the lambda bung on the exhaust manifold and not the pipe, allowing the O2 sensor to inform the ECU without major surgery.
