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Old 01-09-2007, 11:58 PM   #1
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Gear ratios and Compression ratios, explain please?

Gear ratios and Compression ratio's confuse me. How are gear ratio's calculated? I noticed that first gear is usually a higher ratio, and then there's some Final drive...dunno what that means either. Also, how does one come up with a compression ratio? How does one make a compression ratio higher? Lower? What's makes a higher compression ratio better?


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Old 01-10-2007, 02:22 AM   #2
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I am no expert and dont take my word for it but i believe that the first gear is taller like on a bicicle. first gear is a lot talller (bigger) than the last.

Compresion ratio I know the higher the first number is the more air/fuel is in the chamber. Im sure some one else in here has a better idea but this is what i believe lol.
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Old 01-10-2007, 07:19 AM   #3
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Compression ratio is the ratio of how much the cylinder volume is compressed at Top Dead Center (TDC). Say an engine has a compression ratio of 10:1, when the piston moves up to TDC, the total volume of air and fuel is compressed by a factor of 10 (think of it taking 1/10th the original volume)

http://en.wikipedia.org/wiki/Compression_ratio

As for gear ratios, there are actually 2 sets of gears. The first ratio is the ratio of gears from the input shaft to the output shaft. The ratio is how large the input shaft's gear is compared to the output shaft's gear. So with first gear being 3.73:1, the input shaft gear is 3.73 times larger than the output shaft gear. This applies to all remaining gears.

The second set of gear ratios is the final drive ratio. This is the ratio in size between the output shaft and the differential. Usually, there is only one of these gears in a transmission (Getrag 6-speed is special with 2). The final drive multiplies the ratios of the selected gear. So with 1st gear being 3.73:1, and a final drive of 3:82:1, the overall gear ratio is 14.25:1. Changing out the final drive will affect every gear in the transmission.

http://science.howstuffworks.com/gear-ratio.htm
http://auto.howstuffworks.com/transmission.htm
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Old 01-10-2007, 12:30 PM   #4
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Thanks a million Egz!
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