here's what I could dig up from my regions site....you may wanna go to www.SCCA.com
for more in depth rules.
As a rough guide, if your car has modifications beyond this list it is not eligible for Stock Category:
Anything available on the exact model and year of your car as standard or optional equipment, as installed on the factory assembly line (nothing available only dealer-installed is allowed), plus
Standard OEM identical replacement parts
Accessories, gauges, appearance, comfort, and convenience items (not replacement driver's seat, though) that basically don't help
Added roll bar or roll cage to spec (not required, though)
Driver harness (no cutting seats to install, though)
Trailer hitch and/or tow bar mountings
Any wheel of diameter and width identical to a stock or factory optional wheel, offset within +- 0.25 inch
Most street legal tires that will fit the mounted wheels and stock bodywork
Any shock absorber of the same type and mounting as original; no change to standard spring mountings is allowed; suspension geometry may not be altered; gas or hydraulic shocks are permitted
Any brake linings; pre-1992 cars may use solid/braided metal brake lines.
Any front anti-roll bar (no change to stock/optional rear anti-roll bar, if present)
Manufacturer specified ignition settings only
Any replacement air filter element (or removal of air filter element); no plumbing changes, however
Engine bored no more than .020"; no balancing or porting/polishing of head
Replacement of any part of the exhaust system past the catalytic converter (if quiet)
Any oil filter
Added clutch scattershield
Street Touring - S
If your car is a normally aspirated sedan (four seats, four factory seatbelts, not sports-car derived) of 3.1 Liters or less, or one of a few small turbocharged cars specified in the rules, and perhaps prepared further than allowed in Stock Category, it may be eligible for one of the Street Touring Classes. Street Touring - S is an SCCA National class, but Street Touring-R is an optional Regional only class. Street Touring allows anything allowed in Stock, plus (roughly) these modifications:
Any shocks, struts, and springs, using original attachment points
Any sway bars
Any wheels up to 7.5" in width that fit over stock brakes
Tires up to and including a width of 225, with a treadwear rating of 140 or greater.
Strut bars/braces as allowed in Street Prepared.
Exhaust system downstream of catalytic converter(s)
Short throw shift kits
Spoilers, body kits, rear wings, etc.
Pedal kits and other interior cosmetic accessories
Alternate brakes pads and linings
Any fully padded and upholstered front seats with reclining seat backs
Removal of factory trim (rub strips, emblems)
Alternate steering wheels of any diameter, otherwise meeting Stock rules
Cross drilled and/or slotted brake rotors
Alternate air cleaner enclosures
No limited slip differentials except factory viscous coupler type units
Stock brake calipers/drums
Fenders may not be cut or flared (but specific modifications for tires OK)
Emission legal modifications to Engine management system, either electronic or mehanical, but not both.
Engine and transmission must remain unmodified, including emissions equipment