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Old 02-24-2009, 12:12 AM   #1
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Default Center Differential

What is the purpose of it and what is it's tuning effect?
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Old 02-24-2009, 06:51 AM   #2
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You may want to post this question in the offroad thread. Never seen an onroad car with a center diff other than a GT car which is a buggy conversion.

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Old 02-24-2009, 02:33 PM   #3
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Center diffs are used just the same as the front and rear. The front and rear diffs are needed because during a turn the wheels on each side of the car are turning a different speed.

The front tires spin at a different speed than the rear. But not as much of a difference as side to side. That is why in real cars and diesel trucks the center diff is real small. In a 4wd car the front tires are forced to spin the same speed as the rear. The car does scrub some because of this.

The problem is the insane accelleration and power of these cars. An open center diff would just unload to the front and the front tires would be spinning excessively on power.

An AWD car has a center diff and would have more turnin and less steering on exit. It would be nice for turning, but not for straight line speed. It would have to be a very good LSD diff to work. I thought the new LSD diffs would be too stiif and cause offroad cars to be too loose. With a proper setup they engage slow so that they don't lock up until your straight and that helps straight line acceleration.

Then again its another complex and heavy part. If the cars desighn works without it, its better. If one could be made that engages smoothly so that it deosn't start to lock up on turn exit, but is loose in turns and super tight on the straight it could work.

I was abit surpized when I found out that onroad cars were 4WD and offroad were AWD. Go figure.

Is it really needed.
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Old 02-25-2009, 03:18 PM   #4
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With a center diff can you keep a consistent power transfer ratio between the front and rear? Or does it change as the load changes between the front and back?
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Old 03-06-2009, 03:39 PM   #5
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Quote:
Originally Posted by airborneranger View Post
With a center diff can you keep a consistent power transfer ratio between the front and rear? Or does it change as the load changes between the front and back?


No. It only changes output ratio front to rear when the Front comes off the ground it sends extra power there (bad), when the front slips it sends extra power there (bad), or when the car turns it keeps the drivetrain from binding (good). Play with the diffs on your car now. pretend one wheel is the front axle and the other is the rear axle. Center diff works the same. Both output speeds of the diff average out to the input (ring gear) of the diff.

If you wanted to adjust how much power goes where you would need a viscous differential. It is a hydraulic coupler like a torque convertor. The output end of the coupler sends less power to the output end than the input. (it slips when a certain torque level is reached.)

A Lambo uses a VD, so did junky old Explorers. Maybe Porshe to?


You woud run the vd so the input side is on the rear. Rear is mechnically conected, no slip 100% spin. (The input side of a viscous diff has no diff action and is fixed to the carrier) The output side goes to the front drive shaft and slips some.....say 80% torque. The slippage causes heat and frictional loss. Bad for fuel economy.

That would give you 60/40 split. Kinda.
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