1.5 or 2 way diff for track?
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First question is where? We have a front, center, and rear diff.
Front stock is a Torsen, or helical gear diff. It's weak as a unit, not made for extreme motorsports. There is only one kind of aftermarket front diff that is a Torsen and it's made by Quaife, called the ATB diff. These would be considered 1 or 1.5 way diffs.
The Center diff is an open diff stock, and it needs to remain an open diff in order for the ACD to function. The only replacment diff I know of is from the company Ralliart AU, who sell a motorsports level plate LSD.
The rear diff is also open stock and has a range of 1,1.5,or 2 way diffs available from several manufacturers. They are all plate LSD's. Cusco, Carbonetics, Wavetec, and Ralliart are big suppliers. They also make the same plate LSD's for the front.
You have to ask yourself what you want to do:
1) Make a street car / occasional track car more aggressive
2) Prep a race car for time attack or rally, non professional
3) Prep a race car for professional competition
For #1 I would really make it a priority to retain the ACD and AYC systems and focus on the weaknesses of the diffs. Going with a regiment of replacing the front with either a quaife ATB torsen or a 1.5 way plate LSD is always a good idea. Combining it with plate LSD in the rear usually gives Autocrossers and track junkies a few seconds off lap times and the strength needed to keep their setup going, especially if they are on the track more often. Many people with 08's autocrossing aggressively for the past 4 years are breaking their front and rears all the time now.
The center diff has a few upgrades outside of replacing it. Any replacement diff will not allow the ACD to be connected. You can weld pins, get oil pickup upgrades, etc.
Hopefully aftermarket ring and pinion gears will hit the market soon, that is another simple upgrade to either the stockers or aftermarket diffs.
If your really into #2 or #3 up there the most serious path is to disable the ACD and AYC and go for an entire plate LSD from Ralliart Australia. These are heavily built units designed to be pulled apart, adjusted, and rebuilt often in the professional racing world. The stock ACD and AYC clutches cannot compete with the fact that Ralliart offers spare parts and support for these diffs, whereas Mitsu does no support anything with the ACD or AYC beyond replacement T-Cases and Rear diff assemblies.
On all these diffs, 1.5 way is usually the way to go. They offer a more linear, easy to understand power transition. 2 way is a drifter diff for RWD, it dosen't have much of an application for a Evo. 1 way is just not going to cut it unless you have a very specific track or type of racing your targeting.
For most of us looking for an upgrade who want to track occasionally I would recommend going with the Quaife ATB (much stronger than the stock Torsen) and do a 1.5 way, less aggressive ramp angle plate LSD for the rear. This solves the inherent weaknesses in both stock diffs and may give you a better lap time, etc. Not sure how the plate LSD effects the AYC system but people are running it and reporting in more often these days, so better info will be out there soon.
Front stock is a Torsen, or helical gear diff. It's weak as a unit, not made for extreme motorsports. There is only one kind of aftermarket front diff that is a Torsen and it's made by Quaife, called the ATB diff. These would be considered 1 or 1.5 way diffs.
The Center diff is an open diff stock, and it needs to remain an open diff in order for the ACD to function. The only replacment diff I know of is from the company Ralliart AU, who sell a motorsports level plate LSD.
The rear diff is also open stock and has a range of 1,1.5,or 2 way diffs available from several manufacturers. They are all plate LSD's. Cusco, Carbonetics, Wavetec, and Ralliart are big suppliers. They also make the same plate LSD's for the front.
You have to ask yourself what you want to do:
1) Make a street car / occasional track car more aggressive
2) Prep a race car for time attack or rally, non professional
3) Prep a race car for professional competition
For #1 I would really make it a priority to retain the ACD and AYC systems and focus on the weaknesses of the diffs. Going with a regiment of replacing the front with either a quaife ATB torsen or a 1.5 way plate LSD is always a good idea. Combining it with plate LSD in the rear usually gives Autocrossers and track junkies a few seconds off lap times and the strength needed to keep their setup going, especially if they are on the track more often. Many people with 08's autocrossing aggressively for the past 4 years are breaking their front and rears all the time now.
The center diff has a few upgrades outside of replacing it. Any replacement diff will not allow the ACD to be connected. You can weld pins, get oil pickup upgrades, etc.
Hopefully aftermarket ring and pinion gears will hit the market soon, that is another simple upgrade to either the stockers or aftermarket diffs.
If your really into #2 or #3 up there the most serious path is to disable the ACD and AYC and go for an entire plate LSD from Ralliart Australia. These are heavily built units designed to be pulled apart, adjusted, and rebuilt often in the professional racing world. The stock ACD and AYC clutches cannot compete with the fact that Ralliart offers spare parts and support for these diffs, whereas Mitsu does no support anything with the ACD or AYC beyond replacement T-Cases and Rear diff assemblies.
On all these diffs, 1.5 way is usually the way to go. They offer a more linear, easy to understand power transition. 2 way is a drifter diff for RWD, it dosen't have much of an application for a Evo. 1 way is just not going to cut it unless you have a very specific track or type of racing your targeting.
For most of us looking for an upgrade who want to track occasionally I would recommend going with the Quaife ATB (much stronger than the stock Torsen) and do a 1.5 way, less aggressive ramp angle plate LSD for the rear. This solves the inherent weaknesses in both stock diffs and may give you a better lap time, etc. Not sure how the plate LSD effects the AYC system but people are running it and reporting in more often these days, so better info will be out there soon.
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Wavetrac still don't have a diff available for the X which is a pain. Ralliart have their supertraction front diff (it's what Ralliart call the front diff, although disco is technically correct as we are talking in the transfer case here). Of note though, this is for a manual only, it does NOT suit an Evo X equipped with a TC-SST gearbox. This doc should explain it in basic terms what Ralliart have available, or 'had' available... http://www.ralliart.com/GRN/instruction/manual/RA857885S1.pdf
Term Mitsubishi Ralliart new there was a hole that needed filling so they made a front diff for anyone with a Evo X equipped with a TC-SST gearbox.
As for the rear diff, you don't have much choice except stay with stock. Well, you do have a choice but it's a lot of cocking about.
Term Mitsubishi Ralliart new there was a hole that needed filling so they made a front diff for anyone with a Evo X equipped with a TC-SST gearbox.
As for the rear diff, you don't have much choice except stay with stock. Well, you do have a choice but it's a lot of cocking about.
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Not 100% sure but I believe so, the Quaife should be good on SST. Cusco has a plate clutch front designed for the SST, not sure about the other companies.
So would it still make a big improvement just swapping in a Quaife ATB unit on my MR and leaving the centre/rear differentials alone?
Reason I want to leave the centre and rear alone is because of the ACD/AYC but I do believe the stock front differential is less then adequate for the Evo. You DEFIANTLY notice its lack in performance when your ACD/AYC pump is gone/blown. Slow/Medium speed corners are FULL of understeer and feel like you are behind the wheel of a FWD car and any kind of snow/slick conditions makes you question if your car is even AWD...
I have run a Quaife LSD unit in my Twincharged sunfire and it made a night and day difference in tracktion (snow/wet/dry) and even cornering abilities.. I was honestly blown away how much of a difference it made to a FWD car make the power it was.
Reason I want to leave the centre and rear alone is because of the ACD/AYC but I do believe the stock front differential is less then adequate for the Evo. You DEFIANTLY notice its lack in performance when your ACD/AYC pump is gone/blown. Slow/Medium speed corners are FULL of understeer and feel like you are behind the wheel of a FWD car and any kind of snow/slick conditions makes you question if your car is even AWD...
I have run a Quaife LSD unit in my Twincharged sunfire and it made a night and day difference in tracktion (snow/wet/dry) and even cornering abilities.. I was honestly blown away how much of a difference it made to a FWD car make the power it was.
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^ That makes sense, without the pump there is nothing to limit power to the front wheels and most of the time it will understeer hard.
Never have know or talked to anyone that did the Quaife ATB for the front on the Evo X. Knew a guy who had a Quaife installed on an 8. They are known for the quality.
Not sure what kind of performance features it would have over stock. Mostly I understand it to be a much higher material and build quality issue, and hence durability and longevity. Maybe Quaife is the one to talk to about it.
There are theoretical problems with Torsen diffs that make plate LSD's superior for racing. You can rebuild a plate LSD. You can also adjust them. Torsen has serious drawbacks it you go airborne a lot (like in rally).
I would defiantly consider a Quaife if the stock one blew up or I had some kind of T-Case problem.
Never have know or talked to anyone that did the Quaife ATB for the front on the Evo X. Knew a guy who had a Quaife installed on an 8. They are known for the quality.
Not sure what kind of performance features it would have over stock. Mostly I understand it to be a much higher material and build quality issue, and hence durability and longevity. Maybe Quaife is the one to talk to about it.
There are theoretical problems with Torsen diffs that make plate LSD's superior for racing. You can rebuild a plate LSD. You can also adjust them. Torsen has serious drawbacks it you go airborne a lot (like in rally).
I would defiantly consider a Quaife if the stock one blew up or I had some kind of T-Case problem.
Got the new Pump in and WOW my old one must Have been on its way out for a while because it holds corners like its on rails now.. I don't ever remember it being this good... Discogodfather you need to find a way so we can tune the way the pump acts for even better grip
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^Other much more intelligent people are working on it for the X right now. The 8/9 stuff has been out for awhile, they are getting amazing results just with the ACD. ACD and AYC is supposed to be insane, like 5 seconds a lap on a 1 minute circuit.
They are still reading and assembling the tables for the X. With the 8/9 it's a bench the SAWC ECU kind of thing, but it's not to hard. All with open ECU and Op2.
They are still reading and assembling the tables for the X. With the 8/9 it's a bench the SAWC ECU kind of thing, but it's not to hard. All with open ECU and Op2.
This excites me!
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Bump to an old thread. Any updates to this. Insights, ideas, new products etc.
I wouldn't consider TBD's do be 1 or 1.5 way LSD's, those are only reserved for clutch type LSD's.
I'd go Quaife in the front and Cusco RS 1.5 way in the rear.
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I had my first real autocross this past weekend on the Cusco 1.5 rear diff. By "first real" I mean where there was some grip available due to temperature. I don't know if it was me overdriving the car or that the rear diff was putting some crazy power down on the slaloms prior to the sweepers but I felt the car pushing a fair amount on long sweepers. It definitely feels different than the OEM unit.
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To the extent that "2-way" means that the diff locks just as much under engine-braking as it does under power, all helicals (including the OE front and the Quaife for the front) are 2-way. But to call a helical a 2-way may confuse folks, because it's usually the short-hand for a Salisbury (aka modified clutch-pack aka plate-type) diff that has symmetrical legs and cut-outs, such that it locks equally in both directions. But I thought that I'd mention that helicals do lock under engine braking, just for completeness.
The more important difference between helicals and Salisburies is what makes them lock which, in turn, determines when they lock. A helical locks when the reflected values of torque from the two outputs are unequal. (If the concept of "reflected torque" is new to you or makes no sense to you, just think of it in terms of how much torque is being used by each output.) Therefore, a helical does not lock until one of the outputs exceeds its grip limit. This is great for the front of a tarmac car, because it allows the front wheels to turn unequally at corner exit, unless and until you exceed the grip of the inside front tire. Locking the front before you need to is a great way to produce understeer. On the flip side, one weakness of most helicals (i.e., anything less than a T2R) is that they can only produce ratios of output torque, such as 4:1. Therefore, if one output has zero grip, such as lifting the inside front wheel at corner exit, then the diff snaps to wide open. But, in my opinion, that's a suspension error, not a mistake in diff choice.
In contrast to the above, a Salisbury locks as a function of the total amount of torque going through the diff. Because of this, they lock before slip occurs. In fact, their goal is to lock before slip occurs and try to prevent the slip from occurring. As mentioned above, this is not good in the front of a tarmac car, but it's fine for the rear, especially if you have a hard-locking center. Under power, the center and rear lock, but the helical front stays open. Slip is minimized, but you can still steer.
As to the issue of 1.5-way vs 2-way, which is really only a rear-diff question, this boils down to whether you need the rear diff to lock under braking to help keep the tail of the car behind you. On gravel, there's no question: you get a 2-way (but you also get a 1.5-way front, instead of a helical, and this isn't what most people seem to care about). On tarmac, the decision depends very much on driving style. Do you do almost all of your braking before turning in? If so, I'd get a 2-way so you can brake later and even harder. Do you trail-brake, instead? If so, I'd get a 1.5-way, so the rears won't fight each other so much at turn-in.
Of course, the other issue for us is whether you're keeping the AYC. If you are, then you really don't have much of a choice (in the rear) because the only aftermarket AYC-compatible rear diff that I know is the Cusco RS, which is a 1.5-way. You can't put a hard-locking Cusco MZ in the rear of a car with AYC. It's not only incompatible with AYC, but I've recently learned that it won't even fit, regardless of what some websites suggest.
Upshot, in my opinion, for tarmac, leave the front and center alone, maybe get a Cusco RS for the rear, and find someone to retune your ACD/AYC computer. The biggest gains are in the reprogramming.
The more important difference between helicals and Salisburies is what makes them lock which, in turn, determines when they lock. A helical locks when the reflected values of torque from the two outputs are unequal. (If the concept of "reflected torque" is new to you or makes no sense to you, just think of it in terms of how much torque is being used by each output.) Therefore, a helical does not lock until one of the outputs exceeds its grip limit. This is great for the front of a tarmac car, because it allows the front wheels to turn unequally at corner exit, unless and until you exceed the grip of the inside front tire. Locking the front before you need to is a great way to produce understeer. On the flip side, one weakness of most helicals (i.e., anything less than a T2R) is that they can only produce ratios of output torque, such as 4:1. Therefore, if one output has zero grip, such as lifting the inside front wheel at corner exit, then the diff snaps to wide open. But, in my opinion, that's a suspension error, not a mistake in diff choice.
In contrast to the above, a Salisbury locks as a function of the total amount of torque going through the diff. Because of this, they lock before slip occurs. In fact, their goal is to lock before slip occurs and try to prevent the slip from occurring. As mentioned above, this is not good in the front of a tarmac car, but it's fine for the rear, especially if you have a hard-locking center. Under power, the center and rear lock, but the helical front stays open. Slip is minimized, but you can still steer.
As to the issue of 1.5-way vs 2-way, which is really only a rear-diff question, this boils down to whether you need the rear diff to lock under braking to help keep the tail of the car behind you. On gravel, there's no question: you get a 2-way (but you also get a 1.5-way front, instead of a helical, and this isn't what most people seem to care about). On tarmac, the decision depends very much on driving style. Do you do almost all of your braking before turning in? If so, I'd get a 2-way so you can brake later and even harder. Do you trail-brake, instead? If so, I'd get a 1.5-way, so the rears won't fight each other so much at turn-in.
Of course, the other issue for us is whether you're keeping the AYC. If you are, then you really don't have much of a choice (in the rear) because the only aftermarket AYC-compatible rear diff that I know is the Cusco RS, which is a 1.5-way. You can't put a hard-locking Cusco MZ in the rear of a car with AYC. It's not only incompatible with AYC, but I've recently learned that it won't even fit, regardless of what some websites suggest.
Upshot, in my opinion, for tarmac, leave the front and center alone, maybe get a Cusco RS for the rear, and find someone to retune your ACD/AYC computer. The biggest gains are in the reprogramming.
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Your stock front is a helical, not an open diff.
Your center diff is an open spider-type with an active limited-slip device. Without a working ACD/AYC pump, it's wide open.
Your rear diff is a 50/50 planetary with an active AYC device. As above, without a working pump, it's wide open.
I think that's expected behavior, moving from an open to a clutch-type. A clutch-type is supposed to lock wheel speeds together naturally, and then the AYC modifies the behavior subsequently. You should feel some initial understeer due to locked wheels, but it should also feel a bit more planted when you get on the power.
Open, but controlled by other things, as opposed to clutch plates, or gear sets within the diff itself.
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