This is a summary of important SCCA Auto-X (Solo II) rules, with a special emphasis on classes that the 2.5 RS and the WRX can run in, listing which popular mods are allowed in which class. It should answer the most common question, but it does
not replace the
official rule book, which contains the full details for all the points mentioned here, plus many more rules. There is also a number of links to additional valuable resources at the end of this post.
Last modification: March 24, 2005 (update with 2005 rules)
Classes
Which class you are running in is decided by the car model you drive, plus a category depending on the modifications you make to your car. With increasing levels of modifications, a logical progression is from Stock category (cars with no or minimal modifications) over Street Touring, Street Prepared to Street Modified. There are categories beyond Street Modified (Prepared, Modified) that are not within the scope of this document.
The possible classes for a 2.5 RS are:
- Stock: GS
- Street Touring: STS (STX, STU)
- Street Prepared: DSP
- Street Modified: SM
The possible classes for a WRX are:
- Stock: DS
- Street Touring: STX (STU)
- Street Prepared: ESP
- Street Modified: SM
The possible classes for an STi are:
- Stock: AS
- Street Touring: STU (supplemental class)
- Street Prepared: ESP
- Street Modified: SM
The possible classes for a Forester XT are:
- Stock: DS
- Street Touring: STU
- Street Prepared: ESP
- Street Modified: SM
The possible classes for a Legacy 2.5GT are:
- Stock: DS
- Street Touring: STU
- Street Prepared: ESP
- Street Modified: SM
One essential principle is common to all the rules: If a modification is not explicitly authorized by the rules, it is not allowed, no matter how trivial it seems.
Stock Rules (DS, GS)
The following modifications are allowed in stock class:
- Port installed options: rear spoiler, diff protector, armrest extension (specifically allowed in February '03 FasTrack, the general rules allow factory options only).
- Appearance, comfort and convenience options, e. g. gauges, alarms, turbo timers, shift knobs.
- Removal of spare tire, tools and jack.
- Harness (seat belts cannot be removed).
- Any DOT approved tires (see rules for restrictions), including R-compounds, of any size (no modification of fender well).
- Wheels (stock size only, offset within 0.25" of stock).
- Wheel spacers (resulting offset within 0.25" of stock).
- Lug nuts.
- Brake pads, speed bleeders.
- Shocks that maintain stock ride height, can be adjustable. See rule book for details!
- Front sway bar.
- Different alignment using factory adjustments (no camber bolts).
- Spark plugs.
- Air filter element can be removed or replaced.
- Cat-back exhaust.
STS Rules
All modifications from the Stock rules are allowed, except for:
- Tires only up to 225 width, and at least 140 tread wear rating.
In addition, the following modifications are allowed:
- Remove air condition.
- Pedal covers.
- Seat (fully upholstered seating surface, must weight at least 15 lbs).
- Removal of factory emblems (debadging).
- Rolling of inside fender lip.
- Addition of body kits.
- Replace rear wing and bumper covers (wings up to 8 square feet).
- Wheels up to 7.5" width, any diameter.
- Cross drilled and/or slotted brake rotors (standard size).
- Brake lines, e. g. stainless steel.
- Air ducts for brakes.
- Disabled ABS (not removed).
- Shocks (fewer restrictions than stock). No electronic adjustment, like Tein EDFC!
- Springs (can be height adjustable, e. g. coilovers).
- Any suspension bushings, non-metallic.
- Any differential mount bushings, non-metallic.
- Any subframe mount bushings, non-metallic.
- Adjustable camber plates (caster adjustment allowed).
- Camber bolts.
- Adjustable front control arms (only if no front camber plates or camber bolts are used). Must have non-metallic bushings, spherical bearings are not allowed.
- Adjustable rear lateral links (only if no rear camber plates or camber bolts are used). Must have non-metallic bushings, spherical bearings are not allowed.
- Rear sway bar, mounts, end links
- Strut bars (not triangulated).
- Battery, relocation of battery (to trunk).
- Air Intake.
- Headers.
- Reprogrammed ECU or piggyback that controls ignition and fuel by modifying inputs to ECU.
- Short-throw shifter.
- Crankshaft and accessory pulleys.
- Engine mounts (non-metallic).
STX Rules
All modifications from the STS rules are allowed. In addition, the following modifications are allowed:
- Tires up to 245 width.
- Wheels up to 8.0" width.
- Brake rotors (diameter equal or larger than factory, ferrous or aluminum alloy).
- Brake calipers (original attachment point).
- Brake dust shield modifications to accomodate alternate rotors and calipers.
- Uppipe (can be catless).
- Turbo-back exhaust. Must contain at least one (high-flow) cat placed not more than 6" after the original exit of the last factory cat.
- ECU reprogramming. Map must have unaltered factory boost maps.
- Piggyback, see STS. No changes to boost control are permitted. Examples of allowed devices: Vishnu Unichip, Cobb Unichip without Boost Control Unit, Apexi S-AFC. Examples of illegal devices: TurboXS Unichip (controls boost), UTEC (acts as a standalone for timing control).
STU Rules
All modifications from the STX rules are allowed. In addition, the following modifications are allowed:
- Wheels of any width (tire width still limited to 245 for AWD vehicles).
Street Prepared Rules (DSP/ESP)
All modifications from the STU rules are allowed, except for:
- Removal of factory emblems (debadging).
- Body kits (only front and rear spoiler allowed).
- Non-standard brake rotors and calipers.
- Front control arms and rear lateral links.
In addition, the following modifications are allowed:
- Some updating/backdating with parts from different model years, see rule book for details.
- Modification (e. g. rolling, cutting) of fenders for tire clearance. Adding of fender flares.
- Seat (fully upholstered seating surface).
- Remove seatbelt for replacement with harness that meets safety restrictions.
- Any steering wheel.
- Front spoiler.
- Rear spoiler.
- Removal of radio/stereo.
- Any DOT approved tires (see rules for restrictions), including R-compounds, of any size.
- Wheels of any size and offset.
- Cross drilled and/or slotted brake rotors (ferrous, standard size, no two-piece).
- Brake cylinder.
- Fuel injectors and pump.
- Intercooler (including hoses).
- Intake water injection.
- Turbo-back exhaust (no cats required).
- Clutch (metal).
- Flywheel (metal).
- Shifter and shift linkage, e. g. short throw shifter.
- Transmission mounts (non-metallic).
- Differentials.
- Standalone engine management for non-turbo car (?).
- Port matching (see rule book).
Street Modified
Consult the rule book for details of the Street Modified rules. Street Modified inherits all allowances from Street Touring and Street Prepared. The following does not attempt to list all additional modifications that are legal in this class, it just lists a few popular mods that are common in Street Modified, but not allowed in Stock, Street Touring or Street Prepared:
- Certain replaced body parts: e. g. carbon fiber hood, fenders.
- Larger hood scoop, hood scoop splitter.
- Removed rear seats.
- Suspension control arms, lateral and trailing links.
- Metal bushings, subframe bushings.
- Different/updated turbo.
- Blow-off valve.
- Intercooler water spray (?).
- Any kind of boost control (MBC, EBC).
- Any other changes to boost control, like the popular resistor mod.
- Engine management systems that modify boost, e. g. Unichip with boost control unit, as sold by TurboXS and Cobb, UTEC, or reflashed ECU with altered boost maps.
- Standalone engine management.
- Internal engine modifications.
- Engine transplant with different Subaru engine.
- Different/updated transmission.
- Steering rack.
Beyond Street Modified
Consult the rule book for Prepared and Modified categories. The following list is just a reminder of a few popular mods that are not allowed in Stock, Street Touring, Street Prepared or Street Modified, they will put you into Prepared/Modified classes where you will be competing with race cars:
- Replaced body parts not allowed in SM: e. g. trunk lid, STi bumper beams (?).
- Weight reduction not explicitly allowed in SM: e. g. gutted interior, removed heater, wipers, lights.
- Tires that are not DOT approved (racing slicks).
- Anti-Lift Kit (relocates suspension mounting points).
- Braces other than strut tower braces: triangulated braces (V-braces), lower arm braces.
Not Allowed In Any Class
The following are not allowed in any class:
- Nitrous (bottles not allowed on event sites for safety reasons).
Uncertain Mods
No clear rules are currently available for the following popular mods:
Common Questions- Can I run 17" wheels in Stock on my WRX? They are a factory option!
No, the 17" wheels are a dealer installed option, and are not allowed in Stock.
- Why is my XYZ mod illegal? I ran with it all year, and tech never said anything!
Tech inspection is only responsible for checking if your car is safe. Properly classing your car is your own responsibility. Unless somebody files a protest, nobody will check if you have illegal mods for your class. Even if nobody ever protests, many people think that running with illegal mods is unfair and shows a lack of respect for your fellow competitors.
Additional Resources
Official rule book (available for download)
FasTrack (official SCCA publication containing latest rule changes)
Solo II information on SCCA web site
Rules on moutons.org (partly outdated)
Rules in table form (seems to have a few mistakes)
Rule and car setup information at subrew.com
SCCA Forums (message boards)
Solo2.org (message boards)
