I'm not exactly a know-it-all, so please bear with me on this. What do things like 10:1 compression ratio or 3:73 gears mean? As in what does the 3:73 mean or the 10:1 mean? I'm just curious and don't know what these mean. Sorry if this is dumb.

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86' IROC-Z
5.0L TPI
Stock(for now)

 

Not dumb, just basic.

the "3.73" is the gear ratio in the rear end. It means that the driveshaft turns 3.73 times for each revolution of the wheels. Higher numbers mean higher engine RPM at any given vehicle speed, which translates to more power at low vehicle speeds but lower top speed (usually) and higher cruise RPM. Gears have discrete numbers of teeth, so in the case of 3.73s, there are 11 teeth on the pinion and 41 on the ring. 3,42s have 12 and 41, 2.73s have 15 and 41, 4.11s have 9 and 37, etc. Divide the one by the other to get the ratio.

"10:1" is the compression ratio of the engine. It means that there is 10 times as much volume in the cylinder when the piston is all the way down than when it's all the way up. Higher compression = more power by making fuller use of the energy produced in combustion; however it also increases the chance for early uncontrolled explosion of the fuel mixture rather than a smooth burning, thereby requiring higher-octane gas.

Make more sense?

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"So many Mustangs, so little time..."

 

Oh yes, it makes so much more sense now. Thanks.

 

They are ratios. The 10:1 compression means that the total volume of the air in the cylinder will be compressed down from a size of 10 to 1. If the cylinder drew in 10cc (cubic centimeters) of air, the piston movement would compress that air down to 1cc. 34cc down to 3.4cc or 58cc down to 5.8cc would all be 10:1 ratios.
The gears are another ratio, though it should be 3.73:1. For every 3.73 turns of the driveshaft, the axles (and your wheels) will turn 1 time. Try this link for a more in-depth explanation.

Hope that helps.