guitar maestro said:
can someone please explain "compression ratio" and how it affects milegage, fuel type, power, torque?
i'm an undergrad physics major, so i'm not looking for a layman's explanation, but rather a scientific one
The compression ratio equals the ratio between volume of the cylinder at TDC and BDC.
compression ratio has nothing to do with mileage.
the higher the compression ratio, the higher the octane you need. 87 is for 9:1 engines, and 93 (or 92 or 91) is for 10:1 engines. There are some exceptions, but not many. Octane is also dependant on ignition timing. you can run 87 in a car designed for 93, but you will need to remove timing (bring the ingition point closer to TDC.
The higher the compression ratio, the more torque. this is a small change, and torque is more effected by stroke.
overall, a higher compression ratio increases efficiency. however, you must have better fuel, and if high enough, better parts.