Is evo 'real' full-time AWD?
Feb 3, 2013, 06:40 PM
#32
Evolved Member
yes, 4g63 is a stronger block..
also, to complicate things further...
Evo X, and evo 4 - 9 (but not in the USA) are, and have been, equipped with AYC rear diff which allows for true torque vectoring. In other words it will shift torque between the rear wheels (at will) thus actively pushing nose into the corner..
It is a weird system, but devastatingly effective and great fun to use
also, to complicate things further...
Evo X, and evo 4 - 9 (but not in the USA) are, and have been, equipped with AYC rear diff which allows for true torque vectoring. In other words it will shift torque between the rear wheels (at will) thus actively pushing nose into the corner..
It is a weird system, but devastatingly effective and great fun to use
Feb 3, 2013, 06:48 PM
#33
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to put it simply, evo with ACD works in a following fashion:
1. there is a normal open diff mounted in the gearbox that works as a centre diff. It splits the torque 50/50 front and rear. Both it's output shafts go into the transfer box (where you can also find the front diff and 90 deg "transfer gear" that takes torque to the rear). Being a open diff, it will allow for different speeds of front and rear axle while keeping the same set 50/50 torque between the axles.
2. In the transfer box both front and rear output shafts go into the right side of the transfer box where both are connected togeather trough a set of multiple steel plates. These plates provide resistance to relative difference in speed between front and rear output shafts. The ammount of "resistance" is relative to the pressure that is applied by a hydraulic piston onto the clutch pack. Since the hydraulic piston is controlled by a ACD ECU, we call the sytem Active.. as in Active centre differential. In other words, by clamping onto the clutch pack, we can transfer torque between the two axles.. BUT WE CAN ONLY TRANSFER TORQUE IF THERE IS A DIFFERENCE IN SPEEDS BETWEEN THE FRONT AND REAR AXLE
3. If the car is driving normally in a straight line, there is no difference in speeds between front and rear axles. However, if we get a loss of traction on one axle, then by clamping on the centre diff we will transfer torque to the axle with better traction, or even more simply put, we will increase the ammount of traction the car has..
4. It gets more interesting in the corners... In a corner the front and rear axles do not run at the same speed.. So, if we "open" or "close" the central diff we can, in effect, transfer torque between the front and rear axle even if we do not have a loss of grip.
By actively managing the pressure on the clutch pack, we can fine tune the balance of the car... By closing the central diff, we get more understeer, but more grip also.. Opening the central diff, the car will tend to oversteer more..
Normal programing of the ACD usually opens the central diff on corner entry, to provide for better turn in, and then closes the diff on corner exit. The speed at which it opens and closes the diff depends on the ACD program you choose. That is why in SNOW mode the car is more neutral and slower to change the direction.
Also, the ACD takes into account G sensors on the car, steering wheel angle, throttle position, etc..
As you can see, there is much greater refinement in the way ACD works, in relation to normal viscous diff, and greater scope for fine tuning by ACD reprogramming..
1. there is a normal open diff mounted in the gearbox that works as a centre diff. It splits the torque 50/50 front and rear. Both it's output shafts go into the transfer box (where you can also find the front diff and 90 deg "transfer gear" that takes torque to the rear). Being a open diff, it will allow for different speeds of front and rear axle while keeping the same set 50/50 torque between the axles.
2. In the transfer box both front and rear output shafts go into the right side of the transfer box where both are connected togeather trough a set of multiple steel plates. These plates provide resistance to relative difference in speed between front and rear output shafts. The ammount of "resistance" is relative to the pressure that is applied by a hydraulic piston onto the clutch pack. Since the hydraulic piston is controlled by a ACD ECU, we call the sytem Active.. as in Active centre differential. In other words, by clamping onto the clutch pack, we can transfer torque between the two axles.. BUT WE CAN ONLY TRANSFER TORQUE IF THERE IS A DIFFERENCE IN SPEEDS BETWEEN THE FRONT AND REAR AXLE
3. If the car is driving normally in a straight line, there is no difference in speeds between front and rear axles. However, if we get a loss of traction on one axle, then by clamping on the centre diff we will transfer torque to the axle with better traction, or even more simply put, we will increase the ammount of traction the car has..
4. It gets more interesting in the corners... In a corner the front and rear axles do not run at the same speed..
So, if we "open" or "close" the central diff we can, in effect, transfer torque between the front and rear axle even if we do not have a loss of grip. By actively managing the pressure on the clutch pack, we can fine tune the balance of the car... By closing the central diff, we get more understeer, but more grip also.. Opening the central diff, the car will tend to oversteer more..
Normal programing of the ACD usually opens the central diff on corner entry, to provide for better turn in, and then closes the diff on corner exit. The speed at which it opens and closes the diff depends on the ACD program you choose. That is why in SNOW mode the car is more neutral and slower to change the direction.
Also, the ACD takes into account G sensors on the car, steering wheel angle, throttle position, etc..
As you can see, there is much greater refinement in the way ACD works, in relation to normal viscous diff, and greater scope for fine tuning by ACD reprogramming..
So: No throttle = open diff. On throttle = can be open or lock diff with 50:50 split dependent on the conditions detected by the ACD ECU?
Maybe. It's more likely that the 4G63 is platform that has been around much longer and has much more aftermarket support and existing development.
Feb 3, 2013, 11:11 PM
#34
Evolved Member
Also, it is not just lock or open... it will vary the pressure on the plates so you will have various amounts of slippage between the front and rear axles.. depending on the program
Feb 4, 2013, 01:14 AM
#35
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I have another question
,I guess the evo oversteering in this video below is not caused by a faulty ACD/AYC, it is actually how the ACD work. As the driver released the throttle so ACD start opening the diff, but the steering wheel not centered yet, so the oversteer occurs, am I right? Is there any way to save it before crash?
Feb 4, 2013, 02:31 AM
#36
Evolved Member
he hit the painted line on the edge of the circuit... that was his problem.. not ACD and he did not react promptly with steering and throttle..
my suggestion is to stay on the throttle when the car starts sliding around.. in my experience, EVO's do not like to be coasting around without brake or throttle..
but that is something that you need to practice... snow is best..
but be carefull
here is my close call from this winter.. Subaru chase car almost parks in my door..
my suggestion is to stay on the throttle when the car starts sliding around.. in my experience, EVO's do not like to be coasting around without brake or throttle..
but that is something that you need to practice... snow is best..
but be carefull
here is my close call from this winter..
Subaru chase car almost parks in my door..
Feb 4, 2013, 03:50 AM
#39
Evolved Member
unfortunately, we had only a couple of weeks of snow on the roads... however, managed to get 10 really great nights of driving... One tank per drive.. My bank account hurts.. as do all the thin plastic inside wing protectors and front lip..
Feb 4, 2013, 06:29 AM
#41
actually, it depends on the programming... you can have locked diff under braking, if you get it programmed like so..
Also, it is not just lock or open... it will vary the pressure on the plates so you will have various amounts of slippage between the front and rear axles.. depending on the program
Also, it is not just lock or open... it will vary the pressure on the plates so you will have various amounts of slippage between the front and rear axles.. depending on the program
Feb 4, 2013, 03:36 PM
#42
Evolved Member
I have found the same... But, you really need to setup the car right for the corner entry.. and not be affraid to get the car sliding a bit on the brakes... then it works really well..
I would say that a remapped ACD (properly done) is faster for sure.. just needs to be driven well... Mid corner and corner exit especially it is much better than the stock one..
For the record.. my car has AYC, and I run stock tarmac map (which is best for me for "normal fast road driving and some sideways fun", and two modded maps. Also, remapped ACD works wonders in the snow... car is much easier to handle, more natural and changes direction much faster..
I would say that a remapped ACD (properly done) is faster for sure.. just needs to be driven well... Mid corner and corner exit especially it is much better than the stock one..
For the record.. my car has AYC, and I run stock tarmac map (which is best for me for "normal fast road driving and some sideways fun", and two modded maps. Also, remapped ACD works wonders in the snow... car is much easier to handle, more natural and changes direction much faster..
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