Why a shorter rear gear will accelerate the car quicker
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It's a matter of applying power pulses from the motor (or work) to the tire. | It's a matter of applying power pulses from the motor (or work) to the tire. | ||
| − | An 8 cylinder motor will have 4 power pulses for each 360 degree revolution of the crankshaft. It doesn't have 8 like you might think because it's a 4-cycle motor. With any given cylinder in your motor, it takes about 180 degrees to pull in the fresh fuel/air mixture, 180 degrees to compress the mixture, 180 degrees to push down on the piston and transfer work to the crankshaft and 180 degrees to push the burned mixture out of the cylinder. 4 times 180 degrees equals 720 degrees to complete a cycle, or 2 complete 360 degree revolutions of the crankshaft. So, for each 1 revolution of the crankshaft, only 4 of the 8 cylinders in your motor will have fired to produce work. | + | An 8 cylinder motor will have 4 power pulses for each 360 degree revolution of the crankshaft. It doesn't have 8 like you might think, because it's a 4-cycle motor. With any given cylinder in your motor, it takes about 180 degrees to pull in the fresh fuel/air mixture, 180 degrees to compress the mixture, 180 degrees to push down on the piston and transfer work to the crankshaft and 180 degrees to push the burned mixture out of the cylinder. 4 times 180 degrees equals 720 degrees to complete a cycle, or 2 complete 360 degree revolutions of the crankshaft. So, for each 1 revolution of the crankshaft, only 4 of the 8 cylinders in your motor will have fired to produce work. |
I don't want to confuse you, but I have to explain it that way in order for you to do some calculations on your own. We'll use a 2.73 and a 3.73 rear gear for this explanation. | I don't want to confuse you, but I have to explain it that way in order for you to do some calculations on your own. We'll use a 2.73 and a 3.73 rear gear for this explanation. | ||
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Using the 3.73 gear (shorter), the tire is turning 804 rpm's under the same conditions (3,000 divided by 3.73) and rolling 70,752 inches (88 times 804). Getting the same 12,000 power pulses, divide 70,752 by 12,000 and find that the tire is getting a power pulse each 5.896 inches of its circumference or a total of 14.9 power pulses for each 1 revolution of the tire. | Using the 3.73 gear (shorter), the tire is turning 804 rpm's under the same conditions (3,000 divided by 3.73) and rolling 70,752 inches (88 times 804). Getting the same 12,000 power pulses, divide 70,752 by 12,000 and find that the tire is getting a power pulse each 5.896 inches of its circumference or a total of 14.9 power pulses for each 1 revolution of the tire. | ||
| − | + | Now you can see, with the shorter gear, more work is being applied to the tire with each revolution of the tire. More work equals quicker acceleration. | |
| − | + | For the same crankshaft speed, the taller gear (2.73:1) will allow the car to go faster, but not get there as quickly. The shorter gear (3.73:1) will allow a slower top speed, but will get there in a hurry. | |
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