D Modified (DM)
Modified Production and GT cars with internal combustion engine displacement
2000cc and under as follows:
A. The Mazda 12A and 13B Rotary engines are permitted in DM with
the following restrictions:
1. No replacement of cast iron engine case segments with aluminum.
236 — 2013 SCCAŽ National SoloŽ Rules
Modified - Appendix A
2. On the 12A engine, only side and rotor housings from 1974 to
1986 engines shall be used.
3. No replacement of 12A or 13B sections such as side plates with
those from other series engines, i.e. Renesis-type parts.
4. On 12A engines, no peripheral-porting or J-porting is allowed.
Bridge-porting that does not cut into the water o-ring is permitted.
On 13B engines, 4- & 6-port: Maximum porting permitted is streetporting.
No bridge-porting, J-Porting, or peripheral-porting.
B. Weight (with driver) vs. Displacement
Piston engines up to & including 1800 cc: 1280 lbs
12A rotary engines w/ porting restriction: 1280 lbs
Piston engines 1801 to 2000 cc: 1380 lbs
13B rotary engines w/ porting restriction: 1380 lbs
C. Performance Adjustments
AWD: Add 200 lbs
Modified Tub: Add 40 lbs
D. Weight Bias Adjustment - with driver sitting in the driver’s seat
RWD w/ less than 51% weight on drive wheels: Deduct 35 lbs
FWD: Deduct 35 lbs
AWD: Not affected
E Modified (EM)
Modified Production and GT cars as follows:
A. Weight (with driver) vs. Displacement
Piston engines up to & including 3200 cc OHC: 1700 lbs
Piston engines up to & including 4500 cc pushrod/OHV: 1700 lbs
2-rotor rotary engines w/ unrestricted porting: 1700 lbs
Piston engines unlimited displacement: 1800 lbs
3-rotor rotary engines w/ unrestricted porting: 1800 lbs
Electric powerplants (non-hybrid) 1800 lbs
B. Performance Adjustments
AWD: Add 300 lbs
Modified Tub: Add 50 lbs
C. Weight Bias Adjustment - with driver sitting in the driver’s seat
RWD w/ less than 51% weight on drive wheels: Deduct 50 lbs
FWD: Deduct 50 lbs

Here is what the SCCA thinks about the advantage of AWD. Above are the modified rules highlighted are the ADDED weight required if you run AWD.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.