[2turboimports]

1) compression really depends on a number of things. You could lower compression with a thicker headgasket, new pistons, larger bore. But it all really works hand in hand.

2) Power is also gained with VE (volumetric efficiency). Turboed cars can reach a higher volumetric efficiency since air is being forced into the heads. It's always a big choice to make when deciding on compression. some say 8.0:1 is good for top end turbo power and others say 8.5 - 9.0:1 is good for topend and nice for some bottom torque. With lower compression the engine will be able to flow a lot more air, more flow = more top end, but the trade off is loss of low end torque since you're relying more on the turbo for hp.

i hope this makes some sense, if there are any errors, someone correct me please. t hanks