ACD Question
Dec 29, 2006, 06:51 PM
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ACD Question
I don't know much about the ACD control, and a friend of mines said that the controls make the rear tires have more power than the front, and change it into a 4WD or a RWD. Is this true?
Just to make sure, because this doesn't sound right.
Dec 29, 2006, 07:53 PM
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Kind of but he isn't quite right. When you are on the gas and the computer decides the car needs more power in the back it essentially becomes rear wheel drive but its still giving power to the front. When you push the ACD button nothing changes unless you are on the gas hard, its not a selector of fwd or rwd or awd. Its just to alert the computer of what kind of road conditions are present.
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Dec 30, 2006, 07:00 PM
#13
Yeah, my 04 STi had a 35/65 F/R split, the newer models have a 41/59 split.
Imagine a standard open diff.
The case houses everything, and the spider gears are mounted to the inside of the case. The spider gears drive two side gears, and the side gears are allowed to turn at different speeds as the spider gears simply rotate to accomodate this.
The "power split" is simply due to the size of the side gears, which are driven by the spider gears. In the Evo, the diff is symmetrical, meaning the spider gears drive symmetrical side gears.
The STi on the other hand, has an asymmetrical center diff, meaning the two side gears are of different sizes.
The smaller side gear produces less torque to the front diff, the larger side gear produces more torque to the rear diff as the larger diameter gear face creates a larger lever arm.
The Sti can "go to 50/50 split" because the electronic LSD clutch mechanism can effectively "lock" the two diff halves together. It's not a true 50/50 differential split because the diff must be locked to get there.
Personally I prefer the feel of the Evo's ACD vs the STi's DCCD. The STi seemed inconsistent and twitchy, and the Evo's ACD is more progressive and stable, probably much to do with it's inherent 50/50 split on a nose heavy car. The Evo's ACD is more like a seasoning on a naturally balanced drivetrain.
Imagine a standard open diff.
The case houses everything, and the spider gears are mounted to the inside of the case. The spider gears drive two side gears, and the side gears are allowed to turn at different speeds as the spider gears simply rotate to accomodate this.
The "power split" is simply due to the size of the side gears, which are driven by the spider gears. In the Evo, the diff is symmetrical, meaning the spider gears drive symmetrical side gears.
The STi on the other hand, has an asymmetrical center diff, meaning the two side gears are of different sizes.
The smaller side gear produces less torque to the front diff, the larger side gear produces more torque to the rear diff as the larger diameter gear face creates a larger lever arm.
The Sti can "go to 50/50 split" because the electronic LSD clutch mechanism can effectively "lock" the two diff halves together. It's not a true 50/50 differential split because the diff must be locked to get there.
Personally I prefer the feel of the Evo's ACD vs the STi's DCCD. The STi seemed inconsistent and twitchy, and the Evo's ACD is more progressive and stable, probably much to do with it's inherent 50/50 split on a nose heavy car. The Evo's ACD is more like a seasoning on a naturally balanced drivetrain.
Last edited by Wheelhaus; Dec 30, 2006 at 07:03 PM.
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