Originally Posted by RaNGVR-4

In a nutshell, no its not that simple because you must take into account grip levels at each wheel, the power the engine is making, ect.. But, for these purposes, it is.

AYC cannot send ALL of the torque sent to the rear to one wheel, just more than 50%. a mechanical differential can only send a maximum of 50% to one rear wheel.




You are thinking about it incorrectly. First, HP is just a function of torque. torque is what differentials "split".

2nd, torque produced by an engine is dependent upon load. thats why load-bearing dynos are better. an engine will only produce its optimal torque under high levels of load.

Now, lets just look at it as a FWD vehicle making 200 lb-ft of torque. if both wheels have enough grip to not spin under acceleration, the engine will see enough load to create 200 lb-ft, and each wheel puts down 100 lb-ft of that total amount.

Lets create a scenario where one of the wheels is now on a surface that has 1/4the grip the other tire does, the other tire having the same grip as before.

Lets look at what happens with certain differential types:

Open diff:
So, we have one wheel on a slippery surface, and theres a certain amount of torque that will make it slip. since we said its 1/4 as grippy, it takes 25 lb-ft to make the tire spin. so, since the diff is a 50/50 split, that means the other wheel is getting 25 lb-ft as well. Because the one wheel is slipping now, the engine has no more load placed on it, and it is only making 50 lb-ft total. The car will still move forward because the one wheel is getting 25 lb-ft, but it wont move fast.

Mechanical LSD:
The mechanical LSD operates in the same way as above, except for one main thing: once the slippery side starts spinning, it "locks up". this does not mean it changes the 50/50 distribution, but rather it is transfering load from the tire with grip to the engine. The engine is now seeing more mechanical load.

This is where calculations get difficult, you would need to calculate the amount of lockup within the diff, ect. But we will just say that it is giving the engine enough load to make 100 lb-ft of torque now. thats split 50/50 again, so the wheel with grip will now get 50 lb-ft to put down to the ground. the car moves forward faster than with the open diff.

Active computer controlled differential (AYC):
Again, same circumstances as the open diff. But, this differential can cange is torque distribution. lets say it can transfer 75% of the torque sent to it to the wheel with grip. This gets even more complicated. But, here are the main effects of this:

Now, the diff is sending 75% of the power to the wheel with grip. The engine is also generating more torque. Because it can put more torque down, the engine sees more load, and generates more power.

Conclusion:
AYC is best, it can put the most power down when one wheel is experiencing decreased grip. So, because the inside wheel while cornering is experiencing less grip, the AYC can put more power down in a corner than both an open diff or an LSD. the fact that it can vary the amount of power it sends to the rear outside wheel means it can use that to alter the yaw angle of the car itself. this balances cornering loads, decreases steering imputs, ect. better handling, less driver feel.....ta-da.



DISCLAIMER: I am not a certified engineer, I have not graduated or been evaluated. This explanation has been very very simplified to get a main point communicated. Im not interested in arguing about it, if you would like to correct me, be my guest.







S-AYC started in the evo 8, it can transfer about 10% more torque than the original AYC. the evo x has the same S-AYC as the 8/9 had, but it is integrated into the S-AWC system.

Originally Posted by kyooch

I'm interested in how the S-AYC plays in, even if you remove the rear diff? I thought it was a computer controlled rear differential?

Originally Posted by Meevo

And, how come the competition models for the lancer evolution then prefer the mechanical lsd still over any even tuned s-ayc? (read that in a post somewhere)

And any bump for differences between tre rear diff upgrade and cusco type rs rear diff?

Originally Posted by RaNGVR-4

It IS a rear diff. really people?

Here you go, this is AYC:

Originally Posted by WheelGap

If you look at the PWRC schedule, almost every round is on gravel or snow and the S-AYC offers no competitive advantage over a standard mechanical diff on loose surfaces and has the disadvantages of greater weight and complexity.

Driving an AWD car on gravel fast means sliding the car through the corner and using the front tires turning to "claw" the car towards the apex. Since the car is sliding, transmitting more torque to the outside rear tire doesn't do anything. Think about a car on ice, once you get the tires spinning, spinning them faster doesn't move the car any faster.

Rally cars use front and rear Salisbury type limited slip differentials, and that's what comes stock in the rear of the Evo from the factory. These differentials have plates like a clutch in them, and the planetary assembly rides in a split carrier that has ramps that engage stub axles on the pinion wheels. Depending on the angle of the ramps, you can control lockup under both acceleration and deceleration. Handling on gravel is all about your diff setup, and you can do things like have the rear diff lock more under braking than the front. This will destabilize the rear of the car in the braking zone making it easier to rotate the car.

Before they were banned, WRC cars used active front and rear differentials which operate similar to our ACD, they had the advantage of easier setup since the handling of the car could be changed by simply changing the diff map and the ability to have a more sophisticated locking strategy than what a purely mechanical diff can provide. They didn't bias torque like the S-AYC, they simply controlled lockup, like the ACD.

The Cusco differential is also a Salisbury diff, it has a bit of adjustability as I believe there are different sets of ramps in each housing, so you can select the lockup by choosing which sets of ramps you set the stub axles in. There's nothing the Cusco can do that the OEM can't since they're designed the same way and I'm sure TRE could modify the OEM with customer supplied ramp angles. The only reason for choosing the Cusco would have to be based on some other criteria like durability, adjustability or ability to lock more than the stocker.

Originally Posted by Meevo

I think he was questioning because GEARS said that the AYC still works when the rear diff has been removed

Originally Posted by Meevo

And then does that mean the cusco is better built than the Tre's upgraded one?

Originally Posted by RaNGVR-4

And if you understood what you were looking at, you would see that the AYC clutch packs are seperate from the differential, thus the differential can be replaced while leaving AYC intact. You guys should stop asking questions and just go do the research yourself.

Originally Posted by GEARS

I guess you'll need to try them both .

Originally Posted by Meevo

Umm that's why I made the thread and asked the questions...
I'm doing the research right now lol
If you're gonna answer the questions, then b*tch about answering the questions, why bother answering?

Thanks for the info though, although I don't know why I'm supposed to understand things that I'm trying to learn/ask questions about

Originally Posted by RaNGVR-4

......the AYC clutch packs are technically seperate from the differential...

Originally Posted by GEARS

I have installed a Cusco limited slip differential into a EVO-7 with S-AYC and the only thing that it's replacing is the factory open differential. The S-AYC is retained but it's not as operational at biasing power to one tire over the other because the limited slip is providing equal lock-up to both tires, kinda fighting against the S-AYC.......

Originally Posted by RaNGVR-4

You are asking the same questions over and over, when they have been answered in the thread before. Such as the AYC clutches being seperate from the actual differential:






Everyone has to learn about this stuff in some way, some people are proactive and do the research on their own.

Originally Posted by RaNGVR-4

It IS a rear diff. really people?