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Information and FAQs

SCCA SoloII Legality Of Popular Subaru Modifications

So you want to start autocrossing (or maybe you already do) but you need to know what class you are in or what mods you can do and not get bumped to a higher class. Keep in mind that this is NOT official and may in fact be incorrect in some ways. This is based upon my interpretation of SCCA Solo rules or actual rulings on specific modifications. I do believe that this is accurate, however I will not be held responsible if you get protested and aren't legal. For the complete rules, order the SCCA Solo rulebook from the SCCA.

Now that I've covered's the table:

LEGEND: Y=Yes, N=No, D=Driver only, P=Passenger only, F=Front only, R=Rear only
Modification Class
(incl. adjustable)
Anti-roll BarsFYYYYYY
Cat-back ExhaustYYYYYYY
Drop-in Air FilterYYYYYYY
DOT-legal R-compound TiresYN2N2YYYY
Underdrive/Lightened PulleysNYYYYYY
Upper Strut Mounts
(incl. Camber/Castor adjustable)
Suspension BushingsNYYYYYY
Seat ReplacementNF3F4F5YYY
Brake RotorsNY6YY6YYY
Limited Slip DifferentialsNN7Y8YYYY
Passenger Seat RemovalNNNNYRY
Anti-lift KitNNNNYYY
Motor MountsNNNNYYY
Forced InductionNNNNNYY
Engine SwapNNNNNY9Y
This List Is Not Even Close To Finished...Stay Tuned...

1 GS: Wheels MUST be stock size and the offset must be within 1/2 inch of stock. (For example, the GC8 (1st Gen) Impreza 2.5RS came with 16x7" wheels so you must use 16x7" wheels (with a close enough offset) to be legal for Stock class.)
2 STS, STX: Only tires with 140 or higher treadlife and with a maximum of 225 (STS) or 245 (STX) width are allowed.
3 STS: The seats must be reclining and full-sized.
4 STX: The seats may be "fixed back" seats but they must be full-sized, upholstered and suspended, and can't have a "solid outer shell".
5 SP: The seats must be full-sized.
6 STS, SP: Brake rotors may be replaced with any metal rotor but they must be the same size as stock.
7 STS: The LSD rule allows only "factory, viscous-type LSDs". However, coupled with the update/backdate rule, I believe this should allow 1998-1999 2.5RSs to update to the 2000-2001 viscous rear LSD.
8 STX: Stock differentials are required for AWD cars (unless they have ALL open differentials) but allows for adding one LSD to cars lacking any in stock form.
9 SM: Engines may be swapped but only from the same company (Subaru to Subaru, Acura to Honda, Toyota to Lexus, etc.).

USDM 2.5RS Stats and Model Year Differences (1998-2003)

Model Year 1998 1999 2000 2001 2002 2003
Colors Available Rally Blue Pearl
Black Diamond Pearl
Brilliant Red
Acadia Green Metallic
Rally Blue Pearl
Black Diamond Pearl
Aspen White
Silverthorn Metallic
Blue Ridge Pearl
Sedona Red Pearl
Aspen White
Silverthorn Metallic
Blue Ridge Pearl
Sedona Red Pearl
Aspen White
Silverthorn Metallic
Black Diamond Pearl
Engine Type 2.5L DOHC Flat-4 2.5L SOHC Flat-4 ("Phase II")
Horsepower 165 @ 5600rpm
Torque 162 @ 4000rpm 166 @ 4000rpm
Redline 6500 rpm 6250 rpm
Top Speed 124 mph @ 5550 rpm in 5th gear (drag limited) ??? (new car is heavier but more aerodynamic)
Wheels 16x7 Aluminum Alloy
16x7 Aluminum Alloy
16x7 Aluminum Alloy
16x6.5 Aluminum Alloy
(Silver)(5 pair of spokes)
Transmissions 5 speed Manual (5MT); 4 speed Electronic Automatic (4EAT)
Center Differential Viscous LSD with 5MT; Electronic LSD with 4EAT
Default Torque Split (F/R) 50/50 with 5MT; 90/10 with 4EAT
Rear Differential Open Viscous LSD Open
Air Intake Sensor Hot Wire MAF Hot Film MAF MAP Sensor
Other 1999 changes
  • Redesigned transmissions
  • "Checkered flag" interior pattern
  • Larger WRX-style fog lights
  • Leather steering wheel
  • Leather STi shift knob
  • Leather shift boot
  • White gauge faces
  • Passenger assist handle
Other 2000 changes
  • 4-door Sedan available (sedan has smaller wing)
  • Cruise Control now standard
  • Leather Interior (option)
  • Performance Gauge Pack (option)
  • Carbon Fiber interior trim (option)
  • Carbon Fiber shift knob (option)
  • Carbon Fiber handbrake handle (option)
  • Strut Tower Bar (option)
Other 2001 changes
  • Carbon Fiber trim now standard
Other 2002 changes
  • Impreza completely redesigned
  • 2-dr coupe dropped
  • 5-dr wagon (2.5TS) added
  • Many features (foglights, scoop, wing, etc.) no longer standard

Performing an ECU Reset

Q: Why do I need to reset my ECU?

A: Over time the computer learns details about the engine and uses them for it's calculations and settings. If you modify the engine (anything from a turbo to simply switching fuel octane) you have changed the variables involved and the ECU must relearn them. It takes a while to relearn this info as it is still using the old environment as part of the equation until the memory is flooded with only data generated after the modification. Over time it would equalize, but resetting the ECU makes it start over and learn the current environment more quickly.

Q: How do I perform an engine reset?

A: Perform the following steps:
  1. Disconnect the negative terminal from the battery
  2. Wait 30 minutes, then reconnect the battery (if you have keyless or security have your keyfob in hand ready to hit unlock/disarm)
  3. Start the engine (DO NOT PRESS THE ACCELERATOR!)
  4. After the engine idles for 10 minutes, shut the car off (even if you're going to drive immediately, shut the car off first, then start it again)
ECU reset is now complete.

Anti-roll Bars

Anti-roll bars are a simple way to adjust the oversteer/understeer tendencies of an car. Larger front bars increase understeer, while larger rear bars increase oversteer. Keep in mind this is in relation to the other bar. When adjusting anti-roll bars for understeer/oversteer, you are really changing the ratio front to back. If you go with sway bars that are TOO large, you can affect the off-road/bumpy-road handling. The front bar on the Impreza 2.5RS is a 19mm bar. The rear bar has been quoted as both 13mm and 15mm (I'm not sure what the deal is with that). The older WRX models use a 19mm/18mm setup while the newer ones use 19mm/20mm. The general recommendation for the 2.5RS is 18mm rear bar for cars with stock suspension and/or automatic transmissions; 20mm bar for upgraded suspensions (e.g., Prodrive, STI V, Leda, etc.) or for use with drivers that are experienced with handling oversteer situations. I had the FHI 18mm bar but later upgraded to the 18-22mm adjustable from Whiteline. Then I added Whiteline springs over AGX struts (with STI Group N mounts) and then later upgraded to a 22mm front bar (also from Whiteline). (I also have Whiteline heavy-duty endlinks on both bars.) I really like the way the car handles with the 22/22 setup.

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