can someone please explain to me the difference between the two? and what each one is used for?

cheers

The impact on power/torque is very small (approx 2% increase per point) however higher CR does allow the engine to be more efficient...

low compression engines are used so that poorer quality fuels (lower octane) can be used. and give lower power.

Higher compression engines need better quality fuels (higher octane) in order to run without pinking but generate more power.



Cheers

Mark

One goes in the race car, the other tows the race car.

To make a camshaft work properly you usualy need higher compression ratio if using longer duration cams.
The trade off is the Octane ratio that you want to use or that is readilly available.

On the Pinto you get 9.2 standard but can run 10.2 on 95 Octane.
More compression is cheap power up to the point you need to change pistons.

Although you do also generally lower compression if you add boost (turbo/super). However that's to offset the fact that what you're pushing in there is already compressed and therefore under higher pressure to begin with.

simply put it is how much air pressure is generated within the cylinder as a result of the compression stage of the 4 stroke cycle.

Compression heats the air/fuel mix for an effective power stroke. The higher the compression the greater the power - (simply put as there are a number of additional variables to consider at the combustion phase)

hope I didn't confuse things further