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Old 01-30-2013, 08:32 PM   #1
Scooby Newbie
Member#: 280283
Join Date: Apr 2011
Default Attn: SCCA STU/X Cars! Rear Differential Mod Petition

hey all,

as you can see, i'm not a subie guy, though I've been a member on this forum for a couple of years. i run an evo 9 gsr in SM, which I'm selling to run an Evo 9 mr in STU or ASP.

the reason I'm posting here is because I'd like to start a petition to allow one of the differentials to be upgraded in STU and STX classes for AWD cars.
I'm not sure how into evos you guys are over here, but the rear diff mod has been revolutionary in terms of evo handling - it really lets you bring the car around on power.

more info about rear diff mods for evos here:

I think it's a good chance for the SCCA to reconsider its position on aftermarket differentials for AWD cars in STU/X. As it stands right now, 2WD cars in ST are allowed to run any aftermarket differential, while AWD cars are not - this rule was originally created to handicap AWD cars, but I think that a handicap like that is unnecessary and much harder for the rules to justify. If any change is possible, now would be the best time, since our AWD cars have shown that they aren't undefeatable (see M3 for details).

This may not have as much impact on STIs, (which I believe have the R160/180 diff - which is already good), but has a definite impact on STX WRXes. There is real benefit to be had by doing this mod - one that was not commonly explored for evos until maybe 2008 or 2009.
Taking a quick glance at the Nationals results last year, WRXes seem to be more or less struggling to be competitive in this class. What the rear diff mod has allowed evos to do is optimize their setup rather than running some huge rear sway bar/other tricks to get the car to rotate, and let the rear differential take care of the corner exit. I think a WRX with this mod would be way more competitive in STU if it were able to do this mod. Drivetrain wise, the WRX doesn't really have a lot going for it - much like the 03 Evos (open front, viscous center, improperly stacked and weak to begin with rear diff) - how many 03-04 evos do you see doing well in a class that limits drivetrain modifications?

To be clear, this goes beyond restacking plates/refreshing the rear diff to factory spec. evo rear diffs were improperly stacked from the factory so that they'd be quieter, smoother, whatever. I believe mustangs with factory LSDs are set up the same way. This is more about mods that add plates and change lockup, like TRE's ($450), or beyond (Cusco, etc.)

Also to be clear, I mean open up the rules to allow one of the diffs of the car to be modified. the rest of the determination is up to individuals. i don't see this as all that outrageous of an idea

The thread I've just started on evom is here:


Let's discuss and send in some letters!
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Last edited by kyoo; 01-31-2013 at 09:35 PM.
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