ratios

[metalhedskater]

can someone explain to me what the compression ratio and gear ratio and what the numbers mean (9.1:1). Compression ratio..... I am guessing it has to do with how much gas can be let into a cylinder.

Thanks

[JekylandHyde]

Compression ratio: http://www.google.com/search?q=define:COMPRESSION+RATIO

Gear ratio: http://www.google.com/search?q=define:Gear+Ratio

[Igovert500]

compression ratio is how much the air/fuel entering into the chamber is compressed by the piston. When the piston is all the way down, the chamber fills with the combustible air/fuel mixture, then the piston compresses that combustible gas. When the piston is TDC (top dead center) it has reached the apex of its movement. Say you start with 10units of air/fuel, when the piston reaches TDC it has compressed those 10 units into 1/10 of their original volume, making them more combustible/volitial. So you would say that the engine has a 10:1 compression ratio.

If you understand the basics of gears, or gear trains, you know that they have a primary driver gear and the secondary gears. Each gear is a different size with different numbers of teeth. As the teeth interact and turn each other, the smaller one must rotate quicker because of its smaller circumference(hence higher rpms) then the larger gear. The ratios are the comparisons of the turns of the input driver gear to the turns of the output gear. So essentially the ratio takes into consideration the sizes of different gears. Say one gear has 40 teeth, and it is being turned by a gear that only has 10 teeth. The gear ratio is 4:1, because that smaller gear must make 4 full rotations to rotate the larger gear one full rotation. Another example, a gear ratio of 3:1 (an 8 toothed gear turning a 24 toothed gear must turn 3x to get the output gear to make one full turn) This means 3x slower rpms of the output gears, but 3x more torque. To learn more about engines and trannys, and how every part comes together in your car
www.howstuffworks.com will help you alot.