Limited slip diff

I have been told that to gain any more performance from my car, the best thing to do would be to add a limited slip diff.or a torque differential. Can somebody explain what these are and what they do.
Are they different things or are they just different names for the same thing. Also what sort of performance gain could I expect and what brand or model is best. I currently have 192 BHP but I have been told that to increase the BHP any more would make the car run 'lumpier'
TIA
Cossie Beater
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I'm not sure what a "torque differential" is (maybe you mean a "Torsen") but a limited-slip diff is a device that restricts the amount of sped differential between the two axles. While it still allows one wheel to go faster than the other for cornering, it transfers power away from the faster wheel if the latter starts spinning freely.
There have been various designs, including ones with clutches or brake bands of various designs. The Torsen (which has been described in many places, you can undoubtedly find info on the Web if you look), is a specialized type of limited-slip diff, using a special gear design. It has been used in some high-end 4-wheel drive machines.
Lately these devices are being replaced with traction control, which uses a computer to control a combination of ABS brakes and throttle retardation to control torque to slipping wheels more precisely than any purely mechanical device can do. Over here in North America we can get this on high-end Focus models i.e. ZX5, ZTS and ZTW.
All
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In an "open" differential like yours and mine, only one wheel receives power at a time. In a limited slip differential, power is sometimes applied to both wheels through a system of clutches. There are many variations among manufacturers and models. If you are lighting up your tires constantly, maybe a limited slip differential will help your performance but other than that, I can't see what it will do. It is a big help in wet and slippery conditions though. Good luck. jor

is
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snip...
Not even close, much better results will be had by adding four wheel drive :-) /per
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is
My 2001 Zetec 2.0 has ESP (Electronnic Stability Program) which acts not unlike an LSD.
A basic differential allows your driven wheels to rotate at different speeds, which means you can go round corners comfortably, but theoretically, when travelling in a straight line, you don't need a diff. The problem when you are trying to get a lot of power onto the road is that if one of the tyres breaks traction, and you have a standard diff, you just get loads of wheel spin on that wheel and your car doesn't go anywhere...
A limited slip diff prevents that by using a clutch system to limit the speed difference between the two wheels. The degree of slip is varied by adjusting the clutch pressure in the diff. Taken to the extreme, you can have a totally locked diff, which is going to allow you to get maximum power on the road. Problem with that is, that it is a dog when going round corners. Also, the car gets very twitchy on bumpy roads, because if one wheel leaves the ground for an instant, instead of that one spinning merrily until it meets the tarmac again and the car continuing in a straight line, the wheel in contact with the ground is still being driven and the car darts sideways.
In really fancy cars these days (for which read "world rally cars"), the differentials are usually electronically controlled and the amount of slip can be varied to suit the surface they are driving on.
Tim
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