Race Car Stuff

18.1 MODIFIED PRODUCTION-BASED CARS

Classes DM and EM contain production-based cars which are permitted
additional modifications beyond those allowed in Prepared
classes BP through GP. Models must meet the requirements of
Section 13 (first paragraph), be specifically listed in Appendix A, or
be otherwise recognized by the SEB. The Panoz Roadster is eligible
for competition in DM and EM as a modified production-based car.
The following chassis are approved as clones of the Lotus 7 and are
eligible for competition in DM and EM as modified productionbased
cars: Caterham Super 7, Birken, Locost 7, Rotus Seven,
Stalker V6, Laminar Concepts Viking, Westfield, and WCM Ultralite.
Weight and displacement specifications are as shown in Appendix
A. The following clones of the Shelby AC Cobra are also legal:
Factory Five Racing and High Tech. Weight and displacement specifications
are as shown herein.

A. Bodywork

1. The shape of the body must remain recognizable as that of
the manufacturer’s make and model. The body must be made
of a fire resistant material. Doors, hoods, trunk lids, sunroofs,
hatchbacks, etc. need not function as originally designed.
Bumpers, grilles, lights, glass, and trim may be removed.
Side mirrors and tail/stop lights are not required.

2. Firewalls and floors shall prevent the passage of flame and
debris to the driver’s compartment. For cars having fluid lines
in a non-stock routing over the belly pan, the belly pan shall
have drain holes to prevent the accumulation of fluids.

3. The driver must be provided with clear and unobstructed
access to the driver’s compartment.

4. Interiors may be gutted. The driver’s seat must be securely
mounted. Steering and driver’s seating must be completely to
the left or right of the vehicle centerline. Seating must be
located so that neither of the driver’s hips crosses the
centerline of the car.

5. If the radiator encroaches into the driver compartment, it
must be separated from the driver by a metal bulkhead or
enclosing container.

B. Body and Frame

1. Stock Tub
a. No part of the original outside bodywork between the
original passenger compartment fore and aft bulkheads,
such as doors, rocker panels, floor pan, or frame, shall
have reduced thickness or be replaced with lighter material.

b. A bulkhead is defined as a transverse panel that is a separator
or step between the driver’s compartment and the
engine or main luggage area.

c. In cars where a rear luggage compartment is not totally
closed off from the passenger compartment, the base of
the floor pan step or base of a part-height panel that
would limit rearward travel of the rearmost of seat bottoms
is the rear bulkhead point. If there are built-in seat
track catches or stops, they are assumed disabled for this
definition of travel.

d. Heavier gauge material repairs or heavier replacement
sections are all allowed as long as they closely resemble
the original.

e. No removal of the interior sides of the pillars or tub to
leave just an outer shell.

f. Interior storage compartment doors, luggage/trunk compartment
panels, parcel shelves may be modified or removed.

g. Wheel wells and bulkheads are open to modification as
long as the driver is protected from fire and debris.

h. Floor pan width must match or exceed that between the
insides of the original rockers. Length must be matched
between the original passenger compartment bulkhead
locations. Floor pan is defined in Section 12.7. Longitudinal
structure such as rockers may not cover or overlap the
floor pan width. The full stock floor pan width or greater
must be visible when viewed from directly above for at
least the length of the door openings. The floor pan may
only be cut for drivetrain/exhaust/tire/suspension clearance.

i. Tunnels and other vertical floor pan (12.7) features are
included as part of the floor pan of a stock tub and shall be
at least the original size. They can be longer, wider, and
taller.

j. No car of any sort with a floor pan less than 37-inches
wide for front-engine cars or less than 42-inches wide for
mid- and rear-engine cars shall be allowed in DM or EM.

k. A Stock Tub car over 93-inches in wheelbase may change
its wheelbase and remain a Stock Tub car if the stock rear
bulkhead location and floor pan length are retained.
No weight adjustment.

2. Modified Tub
a. All attributes of a stock tub must be maintained in this
category except as explicitly allowed below. There is a
weight adjustment associated with a modified tub.

b. A modified tub is one that mainly achieves a lower CG and
improved strength to weight ratio.

c. Lightweight replacement body panels, a thinned-down
stock fiberglass body, or a lift-off lightweight shell attached
to the main body structure are examples of a modified
tub when done in the bulkhead-to-bulkhead region.

d. Vertical features above the bottom floor pan plane do not
have to satisfy original minimum size or shape. Note that
the original width and length of the floor pan still have to
meet the original dimensions. Drivetrain tunnels and seat
mounting platforms may be made smaller than stock, with
a Modified Tub weight adjustment. A flat floor pan is legal.

e. Floor pan material and thickness are open under Modified
Tub allowances.

f. Cars with factory wheelbase greater than 93-inches may
reduce their wheelbase to a minimum wheelbase of 93-
inches. The floor pan stock length restriction is waived for
these cars only and they may move their rear bulkhead
location to shorten the car. But in so doing, they fall into
the Modified Tub category. Factory length front door
openings shall be retained, but rear doors, if they were
present, may be eliminated or changed as necessary.

g. All other cars, Stock or Modified Tub, whose factory
wheelbase are less than 93-inches may still change their
wheelbase, but it must be done without violating the floor
pan length as determined by both front and rear factory
bulkhead locations.

h. All series of Lotus 7, 7A, Super 7, and their clone or kit
forms such as Birkin, Westfield, Locost, are automatically
classified as modified tubs. This also applies to the Cobra
and its clones.

i. Tube frame cars are included in this tub category.

3. Materials (all tubs)
a. Ferrous (containing iron) metal must be used for all primary
load-bearing structures of the car. The primary load
bearing structure is the main tub or chassis and its connections
to the suspension. No aluminum cages or roll
bars are allowed. Any ferrous or aluminum alloy is permitted
for suspension arms, location links, and uprights/
spindles. Beryllium and beryllium alloys are not allowed
anywhere on the car.

b. The exceptions to the above are parts of the donor production
cars that were originally non-metal. In all cases,
replacement of these parts or addition of more load bearing
structure must be by metal. Lighter replacement
sections may not be used between bulkheads in a stock
tub without it becoming a modified tub.

c. Lightweight substitute materials such as carbon fiber are
permitted only so long as they are clearly not load bearing
in the primary structure or the suspension. For example:
outer body panels in the central tub region must be attached
in a flexible manner such as with Dzus fasteners if
non-stock material composition or non-stock material
thicknesses are to be used.

d. Cars that have been approved for DM and EM as clones
do not have the freedom to use better strength per weight
structural materials than those originally used in the corresponding
places in the originals. The only exception is
the use of high carbon or chromemoly steel in place of
mild steel.

C. Drivetrain

1. Engines must be derived from production automobiles available
in the USA or elsewhere. Complete race engines derived
from production automobile block designs such as the
Pontiac Super Duty 4 and the Cosworth 16-valve series are
allowed. Motorcycle, snowmobile, marine, or any other initially
non-automotive design is not allowed even if it was also
made available in an automobile. Non-automotive engines
are prohibited. 4-stroke automotive motors shall not be converted
to 2-stroke.

2. Engine and/or transmission changes are permitted within the
following limitations:

a. Original front-engine design must remain a front-engine
design, i.e., no part of the engine block or cylinder head
may extend rearward of the midpoint of the wheelbase.

b. Original rear- or mid-engine designs may be interchanged
with each other, but no part of the engine block or cylinder
head may extend forward of the midpoint of the wheelbase.

3. Non-automotive CVTs are prohibited. Automotive-based CVTs
are only allowed with their matching factory engine.
D. Minimum Weights

1. Weight vs. Displacement
All listed minimum weights are with driver.
DM
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.
EM
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.

2. Performance Adjustments
DM
AWD Add 200 lbs
Modified Tub Add 40 lbs
EM
AWD Add 300 lbs.
Modified Tub Add 50 lbs

3. Weight Bias Adjustment
Bias determined by weighing with driver sitting in the driver’s
seat.
DM
RWD w/ less than 51% of the weight
on the drive wheels Deduct 35 lbs
FWD Deduct 35 lbs
AWD Not affected
EM
RWD w/ less than 51% of the weight
on the drive wheels Deduct 50 lbs
FWD Deduct 50 lbs

E. Aerodynamic Aids

1. These classes are restricted downforce classes. No aerodynamic
tunnels or wings for downforce may be added anywhere
on the car.

2. Unless otherwise specified here, no spoilers in excess of
what is allowed in Prepared Category may be used. No body
section such as hood, tub, roof, or rear deck may be reshaped
to achieve downforce.

3. No sealing skirts or other underbody flow directing devices
may be used except as specified.

4. Front splitters are allowed but shall be parallel to the ground
up to the attachment point to the bodywork. Splitter front and
side radii shall be no less then 1/8-inch. Splitters shall not be
more then 6-inches from the front edge to the point of attachment
to the bodywork or spoiler. The outside fender width in
the rear determines the overall width of the car for both front
and rear spoiler and splitter widths. The fender width is the
minimum width of the bodywork wheel well opening or
fender flare opening around the wheel at the rear axle height.

5. Diffusers are allowed at the rear of the car only and shall
have no more than 25-inches front to back of expanding
chamber. A diffuser is defined as an expanding chamber
between the vehicle and the ground for the purpose of accelerating
air ahead of it to develop low pressure.

6. If the factory production car was supplied with tunnels or
wings, they may remain, but they must be blocked in a safe
manner to prevent them from functioning to provide
downforce. For example, foam or sheet metal may be firmly
attached in tunnels or on wings to ruin their shape or to stop
airflow.

F. Tolerances
A tolerance of ±1/2 inch shall be used when measuring floor pan
dimensions from the car’s original specifications.

G. Other

1. At least 1/2 the width of each tire must be covered by the
fenders, when viewed from the top of the fender perpendicular
to the ground. No sharp edges are permitted.

2. Suspension systems and wheels are free.