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I am considering putting in a SLP 12 bolt 4.11:1 rear axle. Would I gain torque (seems reasonable)? Does anyone know of a formula to calculate the torque I would gain?
Posts: 4 | From: Clearwater, Florida | Registered: Jul 2003
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Rear gear change should not effect the engine making more torque. What ever hp and torque your engine makes is all it will do and the gears will just change the rpm band where the hp and torque come in. If you have an automatic, a torque convertor will multiply torque. Posts: 5682 | From: Dearborn,Mi. | Registered: Feb 2002
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Agree with Greg that a rear gear change will not affect the power and torque made by the engine. For that matter, neither will a torque converter.
However, IMHO, a rear gear change will affect the torque applied to the rear wheels....up to point.
At launch a higher numerical rear gear will apply more torque to the rear wheels than a lower numerical gear. In other words a 4:10 rear gear will apply more torque than a 3:42 rear gear to the rear wheels. The difference or increase in torque is the difference between the two gear ratios. A 4:10 gear will apply approximately 20% more torque to the rear wheels than a 3.42 rear gear.....at the same engine RPM and same transmission gear.
However, once you shift up through the transmission this torque multiplication is complicated by the gear ratios in the transmission. For the same transmission gear, the higher rear gear ratio will apply more torque to the rear wheels. It's just that you can vary the overall gear multiplication between the engine and the rear wheels by varying what gear the transmission is in at any given speed.
Also, at any given speed, the higher the rear gear ratio, the higher the engine speed for the same transmission gear. But, the engine speed issue can be mitigated by shifting to the next higher transmission gear. This transmission gear variablility is what I meant about torque multiplication at the rear wheels up to a point.
Posts: 383 | From: Oakville, Ontario Canada | Registered: Jan 2003
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You won't see anything on a dyno. Some claim the numbers go down slightly as a quirk of the dyno, and you may loose some with the 12 bolt because everything is beefier.
What the 4.10's do is get you into the powerband quicker. The seat of the pants says it's like a new car. Posts: 4222 | From: Winnipeg MB CA | Registered: Feb 2000
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Think of it as using a 20% longer handle to do work. The handle end travels farther and gives you more leverage. In this case, the engine will rotate 20% further to turn the rear wheels. Also if you look at your dyno graph, a 20% increase in RPM from 2500 is about 3000, so your torque number for that engine speed is what you will be applying to the rear wheels at the same speed that were traveling at 2500 before the gear swap.
My .02
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96 Impala SS Black Flowmasters SSOA, WCA, NAISSO Posts: 3403 | From: Woodcliff Lake, NJ, USA | Registered: Dec 2000
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