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Old 18-05-2017, 18:18   #1
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RS vs AYC

I bought a rear RS diff set up for my evo 5 a good few months back but never got round to having it fitted. The reason I bought it was for the intention of pushing the car up to 500bhp but now am considering just keeping it on just under 400bhp, fitting a carbon prop and sorting the suspension. Would I gain any real benefit from the RS diff just for binning the AYC? I remember reading something about it making the car feel more controllable but couldn't find the thread in the search. So in a nut shell, am I better flogging the diff and using the cash for a prop, fit both, or leave it the way it is and flog the RS diff?

Cheers in advance.
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Old 18-05-2017, 18:20   #2
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You'll find with the RS diff set up properly it will push you out of the corners. I prefer the RS diff. Most who have them dont even bother having them set up as far as i can tell though.
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Old 18-05-2017, 18:52   #3
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Originally Posted by RichW View Post
You'll find with the RS diff set up properly it will push you out of the corners. I prefer the RS diff. Most who have them dont even bother having them set up as far as i can tell though.
How would you set one up? Might be a silly question that but didn't realise it would need doing. I'll probably take the car to evotune and have it swapped there. No doubt they'll know what to do with it.
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Old 18-05-2017, 19:13   #4
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Quote:
Originally Posted by chris_mak View Post
I bought a rear RS diff set up for my evo 5 a good few months back but never got round to having it fitted. The reason I bought it was for the intention of pushing the car up to 500bhp but now am considering just keeping it on just under 400bhp, fitting a carbon prop and sorting the suspension. Would I gain any real benefit from the RS diff just for binning the AYC? I remember reading something about it making the car feel more controllable but couldn't find the thread in the search. So in a nut shell, am I better flogging the diff and using the cash for a prop, fit both, or leave it the way it is and flog the RS diff?

Cheers in advance.
The RS diff is a lot more predictable than the Ayc diff imo, you won't really see any benefits from the carbon prop though
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Old 18-05-2017, 19:38   #5
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Originally Posted by chris_mak View Post
How would you set one up? Might be a silly question that but didn't realise it would need doing. I'll probably take the car to evotune and have it swapped there. No doubt they'll know what to do with it.
The diff works by locking up the plates inside it - the amount of plates and pressure on them can be adjusted. The more plates and pressure the less slip the diff will allow.

Mine used to try and lock the inside wheel pulling out of T junctions for instance .... not so good for tyre life
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Old 18-05-2017, 20:55   #6
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The RS diff is a lot more predictable than the Ayc diff imo, you won't really see any benefits from the carbon prop though
Thanks for the advice. You've worked on the car already mate, you remapped it for me a little while back. I've been meaning to book it in. There's a knock at the back I was going to have looked at and timing belt wants done too. I'll probably give you a call next week some time
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Old 19-05-2017, 02:52   #7
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Since I have RS rear with 12 plate upgrade, and AYC on Tommi Mak, perhaps I can advise you a bit.

AYC reminds me a lot of Evo and rod bolts: in the past every Evo getting remap had to upgrade rod bolts.
When did you ever hear of a rod bolt letting go on an Evo, ever? Never.
And there are plenty of 600bhp stock block Evos running too.
So, it was a tune- knock/detonation is so violent potentially it will take out a rod and/or piston even on built motor..
But Rod Bolts.....never fail...

AYC fails predominantly because of combination of lack of maintenance and corrosion of the AYC pump. So as far as failure, even AYC is not prone to failure if maintained. So some say there is a limit..so what is the limit?

So here is my data:
I run a Tommi Mak on stock block on Pump & E85 flex-fuel system on HKS 7460:
HKS 7460 is 470 bhp turbo on pump fuel and I am near that..so lets call it 450bhp at least to be fair.

But I also run E85, and make solid 50-60bhp more, so let's call it 500-510bhp.
AYC has no issue with it. I do change fluid regularly and live in sunny California..so corrosion is not an issue.


Handling, AYC Vs RS.

Today Torque Vectoring is all the rage.
Agree?

Porsche offers it even on its 911 Carrera S as option, and its standard on GT3 991 models.
Focus RS made a career of debut as THE car to have due to torque vectoring.

And...
AYC Is torque vectoring diff, except Mitsu introduced it in 1996, some 21 years ago.

So if torque vectoring is so great, why would AYC be so "poor"?
It's not.

One reason why Evo 8/9 and X handle so great out of the box is ACD + AYC, with equal measure contribution.

So what about RS?
Here is the thing: RS is homologated into Rallying because active diffs have been outlawed. Simple. Not allowed.
But many time attack Evos use ACD +AYC, since no regulations mandate what diff to use.

So how does the RS diff work actually on a car?
Any plated rear diff locks both wheels together...and that introduces understeer.
Plain and simple....until you break traction and swing the rear around.

You heard the comment obve, "My rear inner wheel locks up chirping tires while turning"...that is what's happening.

So indeed when driven to past-traction point and forcing the chassis into a slide, the RS rear is predictable, and controllable.
But it introduces understeer, and so up to the point of breaking traction its not as nice to drive.

What about AYC?
When my Mak was OEM stock totally standard, the AYC was a bit unpredictable.
Caught me by surprise because I was not used to it.
What it would do is suddenly drive the rear outer wheel (Torque vector) and rotate the rear end around an imaginary pivot point of the chassis, establishing a shallow angle to the line of travel...
In reality this is ideal scenario, just that on crappy old tires from 2000 and never having experienced Torque Vectoring this was a bit shocking at first.

Than I installed Exe-Tc RM07 and lowered the car to recommended Exe ride height.
Oh my God: transformed the car.
Suddenly the AYC is as predictable as death and taxes.

As a matter of fact the vigor with which it rotates the chassis in most predictable manner around a corner is incredible.
I literally use it continuously when driving bonkers on B-roads.

The better the tires on the car, the more the torque vectoring assists, because the Evo front end grip is so tire dependent, and anything less than really good spoils the chassis.


So I'll politely disagree with the common rhetoric...as I spend and spent a lot of time researching and analyzing, trying and testing, solutions which I implement on my two Evos. And they are always in top notch shape, not tattered embarrassments of former self.


What I am doing now is upgrading the original AYC Mak diff to Evo X AYC diff.
It will fit. Why?
Evo X AYC is mostly the same as Evo 7/8/9: its SuperAYC, which has the ability to shuffle (Torque Vector) (transfer side to side) 80% more torque/power than original Mak AYC: so it has 180% of torque vectoring of my original.
That should yield even more rotation, that will allow me to lower the rear end down a bit, and soften it to gain more traction...and traction is always good for putting more power for more drive out of the corner and reaching higher cornering speeds.

Normally Evo likes some rake to steer in, so by having more torque vectoring I can flatten the chassis, which will gain rear traction.

And ACD has also been tried in Evo 5/6, mainly in rallying. ACD fits onto MAK transfer case..but computer control is bit more involving because in Evo 7/8/9 the ECU logic was flipped and although the connector is same, the wiring is totally different..but...it can be sorted ...

ACD and AYC in MAk would really make a spacial car: lighter chassis, shorter nimble chassis, with ability to reflash ECU and tune the ACD and AYC control algorithm.
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Old 19-05-2017, 09:02   #8
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Quote:
Originally Posted by alpinaturbo View Post
AYC is not prone to failure if maintained.
Really, do you have intimate knowledge of the mechanics and casing of the AYC to state that? The AYC casing has a definite weak point in it's design and is no where near as strong as an RS differential.

Quote:
Originally Posted by alpinaturbo View Post
So some say there is a limit..so what is the limit?
There is a failure limit to everything. You'd need to know the exact material specification, then carry out stress calculations to work out the load to failure point, which doesn't even take into account fatigue due to cyclic stresses, and no-one is going to do that. So you rely on experience of actual failed units, and at what power/torque the car was running, and at what point it failed to give you an idea.
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Old 19-05-2017, 10:09   #9
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I agree with both of you.

alpinaturbo - I agree with you that the AYC diff is a far superior setup than a locking RS diff in terms of handling characteristics (although this can be a personal preference thing) and corner speed/lap times achievable (which is not a personal opinion, rather a matter of fact)

Clivew - I agree with you that the AYC rear diff is not as robust as the RS diff unit. It is still normally robust enough for cars running 400-450, is it not. After that point, the AYC tends to be more fragile than the RS equivalent...

Thoughts?

Mark H
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Old 19-05-2017, 10:47   #10
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Originally Posted by Rampant View Post
I agree with both of you.

alpinaturbo - I agree with you that the AYC diff is a far superior setup than a locking RS diff in terms of handling characteristics (although this can be a personal preference thing) and corner speed/lap times achievable (which is not a personal opinion, rather a matter of fact)

Clivew - I agree with you that the AYC rear diff is not as robust as the RS diff unit. It is still normally robust enough for cars running 400-450, is it not. After that point, the AYC tends to be more fragile than the RS equivalent...

Thoughts?

Mark H
my AYC rear diff on my old 5 split the casing open on a long sweeping bend, not at speed, and never at more then 400hp. The evo 8 rear diff I replaced it with ran fine for a further few years till I replaced with RS. The only reason I replaced mine for RS was, there was no re-build option for the AYC pump back then, and my pump was bringing the light on in warmer weather

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Old 19-05-2017, 11:43   #11
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So being able to tune acd and ayc was mentioned above, what are they actually changing/adjusting?
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Old 19-05-2017, 12:02   #12
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So being able to tune acd and ayc was mentioned above, what are they actually changing/adjusting?
Two parameters get changed in the maps for AYC/ACD, iirc.

First parameter is the clamping force or release amount sent to the individual clutch packs.
Second parameter is the "conditions" upon which the clamping force is applied.

Someone else will add on to this, I hope, but from memory the steering angle sensor and yaw rate sensors are amongst the inputs which monitor the "conditions", from which the AYC/ACD map tables can determine what to do with the AYC clutch packs in order that a calibrated amount of additional %torque is applied to the outside rear wheel, while ACD on later cars works the front/rear torque split...

AYC differs from LSD.

In an LSD it will "*limit* the amount of slip" from the inside rear tyre. There will still be some amount of slip, but by locking the rear wheels together the power/traction is not totally lost through the spinning wheel.

In the case of AYC, the programming is trying to totally eliminate any inside rear wheel slip before it occurs, by sending more torque to the outside wheel than the inside rear wheel. This also promotes a yaw moment that will also help turn the car into the turn in the same direction as the steering angle, so it works in 2 ways, helping both agility as well as traction.

Only in recent years have some car makers gone down this route. Most systems up until now have had a pseudo-torque bias system that worked by applying the brake on the inside wheel - which just saps away power. Active torque biasing is now beginning to filter down from exotics to more mainstream cars, but it has certainly taken a lot of time to catch up with late 90's Mitsubishi tech (and Subaru as well in early 2000's, I think).

Cheerz

Mark H
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Old 19-05-2017, 12:27   #13
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So you rely on experience of actual failed units, and at what power/torque the car was running, and at what point it failed to give you an idea.
mine cracked the right side cover..

yeah, not as robust by any means, esp with that small gearbox that is added in.. but works wonders in the slippery stuff.. Looking at the new systems coming out by audi and BMW, makes you think about how much Mitsubishi was ahead of the game with ayc/acd
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Old 19-05-2017, 12:35   #14
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Originally Posted by Rampant View Post
Two parameters get changed in the maps for AYC/ACD, iirc.

First parameter is the clamping force or release amount sent to the individual clutch packs.
Second parameter is the "conditions" upon which the clamping force is applied.

Someone else will add on to this, I hope, but from memory the steering angle sensor and yaw rate sensors are amongst the inputs which monitor the "conditions", from which the AYC/ACD map tables can determine what to do with the AYC clutch packs in order that a calibrated amount of additional %torque is applied to the outside rear wheel, while ACD on later cars works the front/rear torque split...

AYC differs from LSD.

In an LSD it will "*limit* the amount of slip" from the inside rear tyre. There will still be some amount of slip, but by locking the rear wheels together the power/traction is not totally lost through the spinning wheel.

In the case of AYC, the programming is trying to totally eliminate any inside rear wheel slip before it occurs, by sending more torque to the outside wheel than the inside rear wheel. This also promotes a yaw moment that will also help turn the car into the turn in the same direction as the steering angle, so it works in 2 ways, helping both agility as well as traction.

Only in recent years have some car makers gone down this route. Most systems up until now have had a pseudo-torque bias system that worked by applying the brake on the inside wheel - which just saps away power. Active torque biasing is now beginning to filter down from exotics to more mainstream cars, but it has certainly taken a lot of time to catch up with late 90's Mitsubishi tech (and Subaru as well in early 2000's, I think).

Cheerz

Mark H

yes, basically the ayc tries to accelerate the outside wheel and this gives a net vector force that is pointing toward the inside of the corner.. as a result it will push the front wheels into the corner.. Also it is adjusted so that it works with some degree of oversteer, hence it is weird to drive in the begining..

ACD and AYC use the same acceleratomers, steering wheel sensors, throttle pot and wheel speed sensors. The difference between stock maps is in how much clamping force there is on the ACD and how quickly it will open and close... Normally the tarmac setting will have the most oversteery characteristic. Of course, you can remap the ecu and you can really dial in the car to your taste..

One thing we found interesting when we worked on the maps is how quickly the ecu reacts to steering input.. in fact it has the most direct influence on the way acd locks up... it is as if mitsubishi made the system not only as a way to increase total grip but to enable the car to have such quick reactions and to change direction well.. I have yet to drive a car that works as well in the snow..
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Old 19-05-2017, 12:40   #15
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Quote:
Originally Posted by Rampant View Post
Two parameters get changed in the maps for AYC/ACD, iirc.

First parameter is the clamping force or release amount sent to the individual clutch packs.
Second parameter is the "conditions" upon which the clamping force is applied.

Someone else will add on to this, I hope, but from memory the steering angle sensor and yaw rate sensors are amongst the inputs which monitor the "conditions", from which the AYC/ACD map tables can determine what to do with the AYC clutch packs in order that a calibrated amount of additional %torque is applied to the outside rear wheel, while ACD on later cars works the front/rear torque split...

AYC differs from LSD.

In an LSD it will "*limit* the amount of slip" from the inside rear tyre. There will still be some amount of slip, but by locking the rear wheels together the power/traction is not totally lost through the spinning wheel.

In the case of AYC, the programming is trying to totally eliminate any inside rear wheel slip before it occurs, by sending more torque to the outside wheel than the inside rear wheel. This also promotes a yaw moment that will also help turn the car into the turn in the same direction as the steering angle, so it works in 2 ways, helping both agility as well as traction.

Only in recent years have some car makers gone down this route. Most systems up until now have had a pseudo-torque bias system that worked by applying the brake on the inside wheel - which just saps away power. Active torque biasing is now beginning to filter down from exotics to more mainstream cars, but it has certainly taken a lot of time to catch up with late 90's Mitsubishi tech (and Subaru as well in early 2000's, I think).

Cheerz

Mark H
Is AYC remapped? Thought it was only ACD?
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