My KTM 380 EXC (2 stroke enduro bike) has an "effective" compression ratio of 7.4 to 1 with the exhaust valve retracted, in the high RPM, high HP position.
The "effective" compression ratio is about 8.9 to 1 with the exhaust power valve in the lower position. The low RPM, higher torque position.
In either position, there is also a small hole in the side of the cylinder bore, to bleed off compression for easier starting. This calibrated leak reduces compression during low speed operation. Has no effect at higher RPM.
Even with an "effective" CR of 7.4 to 1, it pings like crazy unless high octane fuel is used.
Also, it makes about 55HP at the wheel at about 8500RPM. Not at all bad for a low compression, 380cc (23 cubic inch) engine.