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Original Message
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| RE: Rearend Gearing |
| By Gerry Proctor - 11/10/2003 12:02:47 PM; IP 207.133.188.254 |
An appropriate gear ratio is a relationship to the engine's power band and how the vehicle is used, Travis. Horsepower is a mathematical manipulation of torque. So if you have a mountain of torque at low rpm you may also have a very high horsepower number at low rpm. This is a common scenario in supercharged applications. In that regard, a numerically low gear ratio may indeed be appropriate to the application.
It makes no sense to install steep gears in a car whose engine peters out at 4,000 rpm.
The reason you see or hear of "built" cars with factory ratios is that it is much harder for the novice to change gears than it is to install headers, cam, and intake.
You are correct in that this occurance is less than optimal since a car and how it performs is the sum of its parts and how well they compliment each other. And in that regard, it usually has a negative result when you build an engine that doesn't even turn on until it hits 3k rpm but using a 3.0:1 or less gear ratio and a stock converter, if using an automatic.
Yes, the correct gear ratio can completely change the character of the car. But there are not a lot of absolutes so a builder may make high V/E at under 3k rpm and multiply that low rpm grunt with the lower rear ratio.
But rear gear ratio is but one thing in a laundry list of mismatches.
I run a 3.89 geared Detroit Locker because my engine doesn't come up on the cam until around 3k rpm and pulls hard to the limiter at 6k rpm. The engine's bottom end is far too soggy to make use of the factory 3.0 gears. |
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