97itr153

If YOU were recreating an IDEAL EVO for hard-core, skilled enthusiasts, what kind of diffs would you like to have? Front, Center and Rear ?

theheff

How about 3 ATB diffs-- front, center, AND rear? That'd be a serious cornering beast and they're all mechanical w/ instantaneous response! Claudius, what do you think-- would this work?

Heff

MrAWD

You have to be careful with the center diff. More locking or even distribution will result in more understeering of your car. On the other hand more open type center differential will give you more of the RWD feel and oversteering results.

Having a VC LCD in there is a good compromise!


Fedja

theheff

ATB = automatic torque biasing-- like Torsen. Uses worm/planetary gears. Transfers torque before slippage (unlike viscous) but has no clutches to wear out. Basically, a car w/ 3 ATB diffs would transfer 25-25-25-25 to all 4 wheels under normal conditions. But, based on the torque biasing ratio of the diffs (typically 4:1, the max torque split), would transfer up to 64% of available torque to the wheel with the most traction (say 80% to the rear, then 80% of that to the outside wheel on a hard, accelerating corner). All this occurs before slippage.

So in summary, I believe having 3 ATB diffs would ROCK because the wheels with grip get the power AND you don't have to spin (i.e. an inside tire) first.

Sorry, I know this is a crappy description-- you should check out Quaife's website for more info...

Heff

theheff

I think 2 way in front would be a little too intense-- you'd get a lot of tire wear since it's working under accel AND deccel. However, I BELIEVE that a 2 way could in theory get the best lap times, but 1.5 is nearly as fast and not as beastly to handle (or as mean to your tires). Also, 2-way's are clunkier/noiser-- a minus for daily driveability.

seattle944t

I agree this would be a great setup - except there is a serious flaw in this for a Rallye car. ATB diffs act like open Diffs when a wheel is spinning freely (in the air). This would still work for most of the time on a street car. Track days could be a problem though on a bumpy track.
BUT there is a solution - ABS. Using ABS as traction control to apply brake force to the airborne wheel. This allows torque transfer to take place to the wheel(s) on the ground.
Pretty sure this is what Audi does with their latest AWD system, If I recally correctly it's an ATB center and rear diff and open front. The ABS controls a wheel that is spinning at a rate much faster than the others - within about 6 degrees of a wheel rotation.

MrAWD

Difference between the 1.5 and 2 is during the deceleration (braking). In most cases (with the exception for gravel and snow) both front wheels will be under the heavy impact from the brakes and as long as you are in the straight line everything should be fine with both wheels evenly loaded from both brakes and differential. If you do some late braking and getting inside the turn a bit, than inside wheel will have less traction than the outside one and that would not be a good thing to have.

So between the 1.5 and 2 in the front my vote goes for the 1.5 one.

Now, if you want to make things even better, I would go with the torsen type (or ATB from Quaife) diff in the front. The main advantage would be in the torque sensing feature, compared to the mechanical type that others are. ATB will act quicker than the mechanical diff and correct the distribution before the imbalance actually happens.


Fedja

theheff

Agreed-- ATB in front should be sweet. I just got some info from Quaife that they will have an Evo 8 diff in the (hopefully really near!!) future.

chronohunter

iTrader: (1)

We still need to source the Cusco center 35/65, anyone know where to get them and if the hand brake will work? Doesn't the Torsen (ATB) diff in the front have some locking on decel? That would induce corner entry understeer, the very thing we are trying to vanquish from our EVO's. I still feel that a 1-way front would be the way to go. What good is a 1.5 way in the front? Torsen does list on their web site a fully open on decel diff that they make but just not for our car. I suggest we flood them with e-mail requests for it! (torsen@torsen.com)

Have said all this, sitting back looking at my post I feel compelled to add this: after thrashing my car for a week I can honestly say the stock setup works really well. It is very progressive, understeer is there but a strong trail brake rotates the car beautifully pick up the throttle and a nice 4-wheel driff carries you to the exit and in the gravel it is amazing, just pick an angle using the brake on entry and plant the throttle and hang on! So smooth and controlled. That is what has impressed me the most.. the refinement of the complete car at 10/10's it somehow combines razor sharp reflexes with pridictability and progressivity, a very, very rare combination.

Mr. AWD have you tried one yet? (you will love it )
Claudius, you were so right about this car

theheff

ATB's have very minimal locking on decel-- they are very good for road racing/autox because the "locking friction" transitions smoothly w/ applied torque. So in otherwords, the locking under braking essentially varies w/ torque applied-- this is a good thing because under entry/ light braking it is essentially open. Then, when you get on the throttle, instead of it locking up suddenly and breaking tires loose, it smoothly transfers torque based on what each wheel can handle.

BOTTOM LINE: ATB's are the best on tarmac

Heff

chronohunter

iTrader: (1)

You're right, I was reading the Torsen tech stuff on their site and the do say that the locking on decel is minimal. They also stated that it is all adjustable using different washers/shims and in the design by changing ramp angles. I hope they are willing to develop specific applications for ALL our differentials rather than putting in their "generic" versions.