This excites me!^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.
I wouldn't consider TBD's do be 1 or 1.5 way LSD's, those are only reserved for clutch type LSD's.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.
Your stock front is a helical, not an open diff.Wait wait wait, im confused.....the stock diffs are open?! Somebody explain this to me, I thought the rear diff and center were hydro controlled by the AYC pump. Clearly Im confused.
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.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.
Open, but controlled by other things, as opposed to clutch plates, or gear sets within the diff itself.Wait wait wait, im confused.....the stock diffs are open?! Somebody explain this to me, I thought the rear diff and center were hydro controlled by the AYC pump. Clearly Im confused.