USRA Limited Mod body rules

The nose piece and the front bumper can reach no more than 36 in ahead of the front wheel center. (Diagram A1)

Nose

• Rule 1.18, Diagram N Nose width: no more than 42 in, at the top and at the bottom. Keep it flat and flush with the sides. (Rule 1.18, Diagram N)
• Rule 1.18 Nose fins: 2.5 in fins are allowed along both sides of the nose, matching side to side. They can't run past the leading edge of the radiator or the leading edge of the hood. (Rule 1.18)
• Rule 1.18 All the aluminum on the nose, fins included, sits completely inside the outer edges of the front bumper. (Rule 1.18)
• Rule 1.18 Anything between the nose fins counts as nose, and so does anything that separates from the hood. (Rule 1.18)
• Rule 1.18 No concave nose, whatever material you build it from. (Rule 1.18)
• Rule 1.18 Plastic noses and valances (a valance is a panel under the nose) are allowed, part #MD3M21100. A plastic nose needs a horizontal brace in the upper nose filler every 12 in so the panel can't cave in. (Rule 1.18)
• Rule 1.17, Diagram S Nose to ground: keep the nose piece and its skirting at least 3 in off the ground. Plastic skirting on the bottom of the nose piece can be up to 5 in tall. (Rule 1.17, Diagram S)

Bumpers

You need both a front and a rear bumper, with no sharp edges. Officials can turn away any bumper they find unsuitable. (Rule 1.19.2)

• Rule 1.19.1, Diagram T Bumper center height: at least 16 in off the ground, front and rear. Rule 1.19.1 puts the top of the range at 23 in; Diagram T puts it at 24 in. (Rule 1.19.1, Diagram T)

• Rule 1.19.2 Tubing: at least 1.25 in. Each bumper has to carry the car's weight when a tow vehicle lifts it. (Rule 1.19.2)
• Rule 1.19.2 Mount the front bumper across the front of the car, from the end of one frame rail to the end of the other, with its bottom loop parallel to the ground. (Rule 1.19.2)
• Rule 1.19.2 The top bar sits straight above the bottom bar, not off center. (Rule 1.19.2)
• Diagram X On the front bumper, space the bars at least 6.5 in apart, center of the top bar to center of the bottom bar. (Diagram X)
• Rules 1.19.3, 1.19.4 The rear bumper can be flat stock instead of tubing, and it has width and fuel cell rules too; see Deck and spoiler. (Rules 1.19.3, 1.19.4)

The hood stays low and flat, and it seals the engine bay off from the driver. (Rule 1.9, Diagram G)

Hood

• Rule 1.9 Hood rear height: no more than 2 in above the decking. The deck is the flat top panel that runs from the back of the engine to the rear of the car. (Rule 1.9)
• Rule 1.9 The hood is level or slopes down toward the nose. No reverse rake (a hood that rises toward the nose). (Rule 1.9)
• Rule 1.9 Flat from side to side: no bowed or concave hood and no lips. (Rule 1.9)
• Diagram V Hood width: between 24 and 67 in, and it has to cover the radiator. (Diagram V)
• Diagram G Hood sides: they drop no more than 5 in. (Diagram G)
• Diagram M Hood item M: 6 in max. Diagram M marks a raised piece on top of the hood, drawn as a scoop, and doesn't name the part. (Diagram M)
• Rule 1.16 No engine covers. (Rule 1.16)
• Rule 2.9 Brace bars ahead of the roll cage can't sit higher than the "stock hood height". (Rule 2.9)

Engine placement

• Rule 3.15 Engine setback: the rear of the engine (the bell housing flange) at least 70 in ahead of the rear axle centerline, no tolerance. (Rule 3.15)
• Rule 13.2 Mount the radiator ahead of the engine. (Rule 13.2)

The doors and quarter panels (the body sides behind the doors) run flush with the deck. (Rule 1.14)

Doors and quarter panels

• Rule 1.15, Diagram E Body ahead of block: apart from the hood and nose, the bottom of the body can reach no more than 6 in forward of the back of the engine block, on both sides. (Rule 1.15, Diagram E)
• Rule 1.11 No panel in front of the right door, beside the engine compartment. (Rule 1.11)
• Rule 1.1 The doors and rear quarter panels can be fire-retardant plastic or composite (see Body and panels). (Rule 1.1)

Skirts and ground clearance

• Rule 1.17, Diagram S Body to ground: every point of the body, doors and quarter panels included, stays at least 3 in off the ground. (Rule 1.17, Diagram S)
• Rule 1.17 Plastic skirting up to 5 in tall is allowed along the bottom of the doors and quarter panels. (Rule 1.17)

Car width

• Rule 1.19.3 The tires have to be the widest part of the body. (Rule 1.19.3)
• Rule 1.19.3 Side rail bars (nerf bars: tube bars outside the body) can't stick out past the width of the rear tires. (Rule 1.19.3)
• Rule 8.1.8 Car width: no more than 78 in across the widest points. Aluminum spacers between hub and wheel are allowed if the car stays within that. (Rule 8.1.8)

Door bars and door plate

• Rule 2.1 Driver side: at least 3 door bars (the horizontal cage tubes beside the driver), parallel to the ground and square to the driver, welded to the cage at the front and the rear. They have to protect the driver without making it unduly hard to get in or out. (Rule 2.1)
• Rule 2.1 Driver-side door bars and uprights: at least 1.5 in diameter with 0.083 in wall. (Rule 2.1)
• Rule 2.1 Door plate: steel, at least 18-gauge (0.049 in), welded securely to the outside of the driver-side door bars. It covers from the top door bar to the bottom door bar, and from the rear hoop down post to 5 in ahead of the seat. (Rule 2.1)
• Rule 2.1 Passenger side: at least 1 cross bar, horizontal or angled, of at least 1.25 in OD with 0.083 in wall, plus 1 top horizontal bar of at least 1.5 in OD with 0.083 in wall. (Rule 2.1)

The roof runs parallel to the deck front to back and level from side to side, apart from the 5 in of slope allowed below. (Rule 1.6)

Roof

• Rule 1.6, Diagram P Roof slope: no more than 5 in of drop from the rear to the front. With a level laid on the roof, the gap can be no more than 2 in at the rear and 5 in at the top front. (Rule 1.6, Diagram P)
• Diagram K Roof length: between 32 and 53 in, front edge to rear edge. (Diagram K)
• Diagram L Roof width: between 32 and 53 in, roof sides included. (Diagram L)
• Rule 1.6 Roof sides can be up to 4 in, with a ridge down each side of no more than 1 in. (Rule 1.6)
• Rule 1.6 Rear roof stiffener: up to 0.5 in, turned down square to the ground. (Rule 1.6)
• Rule 1.6 Aluminum roofs are allowed. No OEM (factory) Gremlin roofs and no dished roofs. (Rule 1.6)

Pillars and windshield

• Rule 1.3 Front window supports. The posts on each side of the windshield opening have to look like a production car's. A painted roll bar doesn't count. (Rule 1.3)
• Rule 1.5 The windshield opening and its corner posts keep a standard shape, with no streamlining across the top. (Rule 1.5)
• Diagram R Windshield base: no more than 19 in, measured along the base of the windshield from the cowl (the panel between the hood and the windshield) back toward the corner post, the same on both sides. (Diagram R)
• Rule 1.2 Half windshield: an aluminum half windshield is allowed on the driver's side of the front opening only, reaching no more than 6 in past the steering wheel. (Rule 1.2)
• Rule 2.7 A screen or bars are required in the front window opening, in front of the driver's face. (Rule 2.7)

Windows

• Rule 1.4 Window openings: every opening, front, back, left and right, at least 12 in. (Rule 1.4)
• Rule 1.4, Diagram F Side window openings: between 12 and 18 in tall on both sides, measured from the top of the door to the roof. (Rule 1.4, Diagram F)

Sail panels

A sail panel is the side panel running from the roof back to the deck. The two sail panels must be solid and match each other in design. (Rule 1.7)

• Rule 1.7 Front end: start each panel no farther forward than the driver's seat. (Rule 1.7)
• Rules 1.7, 1.8, Diagram Q Rear end: rule 1.7 lets the panel run back to the rear of the deck, no farther, ending within 3 in of the spoiler support. Rule 1.8 and Diagram Q call for a gap of at least 3 in between the sail panel and the spoiler support. (Rules 1.7, 1.8, Diagram Q)

• Rule 1.8, Diagram E Length: rule 1.8 caps the sail panel at 43 in long. The Sail Panels drawing measures that 43 in along the bottom edge, with the top rear tip reaching 4 in farther back. (Rule 1.8, Diagram E)

• Rule 1.8 Height at the rear: no more than 8 in. (Rule 1.8)
• Rule 1.8 Top curve: the top edge can stray no more than 2 in from a straight line drawn from the roof to the rear of the panel. (Rule 1.8)
• Rule 1.8 Bow: no more than 4 in, up and down, between the roof and the quarter panel. (Rule 1.8)
• Rule 1.8 The Sail Panels drawing also shows a curved cutout 8 in deep in the front edge of the panel, not marked as a minimum or a maximum. (Rule 1.8)

• Rule 1.7 Mount it within 1 in of the outer edge of the deck, flush with the outer edge of the roof. (Rule 1.7)
• Rule 1.7 Left and right sail panels can differ in material length by no more than 4 in, measured from the roof line to the deck. (Rule 1.7)

Window net

• Rule 15.13 A full-size window net is required in the driver's window opening on the left side, with its mounts welded to the roll cage. (Rule 15.13)
• Rule 15.13 Recommended: approved racing arm restraints. (Rule 15.13)

The deck has to be covered over. A spoiler on top of it is optional. (Rules 1.14, 1.13.1)

Deck

• Rule 1.14 No drop decks. The deck stays parallel to the frame and level side to side. (Rule 1.14)
• Rule 1.14, Diagram D Deck slope: no more than 6 in in total, with no more than 3 in of that from the racing seat to the rear of the deck. (Rule 1.14, Diagram D)
• Rule 1.14, Diagram C Deck height: the top of the deck at the rear sits between 28 and 41 in off the ground. The 41 in has no tolerance. (Rule 1.14, Diagram C)
• Rule 1.14, Diagram O Deck length: between 98 and 121 in, from the back of the engine to the rear of the deck. (Rule 1.14, Diagram O)
• Rule 1.14, Diagram H Deck width: between 55 and 67 in, measured at the top of the interior deck, and the same from front to rear. (Rule 1.14, Diagram H)

Spoiler

• Rule 1.13.1 If you run a rear spoiler, it is between 1 and 5 in tall and no more than 67 in wide. (Rule 1.13.1)
• Rule 1.13.2 A stiffener is allowed if it sits 1 in or more down from the top edge. (Rule 1.13.2)
• Rule 1.13.3 Up to 3 spoiler braces, mounted in line. (Rule 1.13.3)
• Rules 1.13.4, 1.13.5 Mount the spoiler inside the outline of its braces. No fins, lips or wings. (Rules 1.13.4, 1.13.5)

Spoiler braces

USRA's Spoiler Braces drawing shows the brace shape. Most of its dimensions aren't marked as a minimum or a maximum. (Rule 1.13.3)

• Rule 1.13.3 Length along the bottom edge: 18 in, from the front of the brace to the edge of the interior deck. (Rule 1.13.3)
• Rule 1.13.3 Height: 4 in at the front end and 8 in at the edge of the interior deck. The drawing also marks a 1 in dimension at the top of the brace, a short way ahead of the 8 in height line. (Rule 1.13.3)
• Rule 1.13.3 The top of the brace runs 5 in behind the edge of the interior deck, and its lower rear edge, below the deck edge, is drawn at 45 degrees. (Rule 1.13.3)
• Rule 1.13.3 Top rear corner radius: at least 2 in. (Rule 1.13.3)
• Rule 1.13.3 Break (bend) along the top edge: no more than 0.5 in. (Rule 1.13.3)

Fuel cell

• Rule 7.5.1 Use a commercially made fuel cell, held by at least 2 steel straps that are 2 in wide at every measuring point. (Rule 7.5.1)
• Rule 7.5.2 Enclose the cell in a steel container. Behind the axle, protect it with securely mounted roll cage tubing. (Rule 7.5.2)
• Rule 7.5.3 Fuel cell height: the lowest point of the cell at least 10 in off the ground, and no part of it lower than the protective tubing. (Rule 7.5.3)
• Rule 7.5.3 Fuel cell tubing: the protective tubing can be no wider than 6 in on each side. (Rule 7.5.3)

• Rule 7.5.4 Check valves are required. A cell without a positive-seal filler neck and cap needs a ball-type, flapper, spring or filler rollover valve. (Rule 7.5.4)
• Rule 7.5.5 Capacity: no more than 22 gallons. (Rule 7.5.5)
• Rules 1.19.3, 1.19.4 The rear bumper can be tubing or flat stock. It must protect the fuel cell and can't stick out past the width of the rear tires. (Rules 1.19.3, 1.19.4)

The driver's compartment has a complete floor and firewall, and the driver must be able to get out on either side. (Rule 4.4)

Firewall and floor

The rulebook sets no thickness for the firewall or the floor and doesn't name a metal. (Rule 4.4)

• Rule 15.15 The firewall and floor can't be plastic. Plastic is allowed only from the firewall's edge out to the body skin; the full plastic rule is under Body and panels. (Rule 15.15)
• Rule 1.9 The hood is sealed off from the driver (see Hood and engine bay). (Rule 1.9)

Interior sheet metal

• Rule 4.4 Interior sheet metal can't rise above a standard window opening or close one in. (Rule 4.4)
• Rule 4.4 Run it level from the top of the driveshaft tunnel across to the right-side door bars, or slope it up from the top of the tunnel to the top of those bars. (Rule 4.4)
• Diagram D The top of the interior sits flush with the doors and quarter panels. (Diagram D)

Seat position

• Rule 4.6.3 Seat back: no farther back than the rear edge of the quarter post. (Rule 4.6.3)

• Rule 3.7 You can notch the frame to clear the seat (see Frame and stance). (Rule 3.7)

Cage-to-body fit

• Rule 2.1 Cage tubing: the main four-point cage is continuous hoops of round steel tubing, at least 1.5 in diameter with 0.095 in wall, and officials have to accept it. (Rule 2.1)
• Rule 2.1 Tubing of 1.75 in diameter gets a wall tolerance for manufacturing flaws, down to 0.083 in; tubing under 1.75 in gets no tolerance and needs at least 0.095 in wall. (Rule 2.1)
• Rule 2.5 Build the cage from front and rear hoops joined by side tubing, or from side hoops, all at the tubing sizes above. (Rule 2.5)
• Rule 2.4 Cage mounts: mount the cage to the frame in at least 6 places. (Rule 2.4)
• Rule 2.6 With the helmet on and the driver belted into the seat, the top of the driver's head can't stick up above the cage. The halo (the top hoop over the driver) needs a cross bar. (Rule 2.6)
• Rule 2.8 Foot protection. Required: a bar across the back of the engine, plus vertical bars and rub rails (strips along the body side that take contact) or similar protection. (Rule 2.8)
• Rules 2.2, 15.13 Pad every roll bar within the driver's reach with a material officials accept, and every bar around the driver with approved roll bar padding. (Rules 2.2, 15.13)
• Rule 2.2 Recommended: fire-retardant padding. (Rule 2.2)
• Rule 2.10 No adjustable bars on the frame or the cage. Removable bars are allowed. (Rule 2.10)
• Rules 2.3, 2.11 Officials have to accept the cage's installation and workmanship. A cage that breaks these rules can draw cash fines and other penalties. (Rules 2.3, 2.11)

Build on a 1978 to 1987 OEM GM metric full frame or on the unaltered Speedway replacement frame (#91678881). The metric frame is the separate perimeter frame (it runs around the car under the body) from GM's mid-size rear-drive cars, such as the Monte Carlo, Cutlass Supreme, Regal and Grand Prix. The Speedway frame is Speedway Motors' new-built copy of it. (Rule 3.1)

Which frame

• Rule 3.1 If you're building from a GM donor car (a street car whose frame you convert into the race car), you can use its frame if it is the metric frame described above. (Rule 3.1)
• Rule 3.14 No Jeep, Bronco or similar four-wheel-drive frames, no sports car frames and no front-wheel-drive cars. (Rule 3.14)
• Rule 3.12 No tubular front clips. The front clip is the front section of the frame, ahead of the firewall. (Rule 3.12)

Allowed frame changes

The frame stays full and complete. You can't widen, narrow, shorten or lengthen it, and any change not listed here isn't allowed. (Rules 3.3, 3.11)

• Rule 3.5 The front frame horns (the front ends of the rails, ahead of the radiator) can come off ahead of the steering box. (Rule 3.5)
• Rule 3.6 You can cut the front frame for radiator clearance, and for nothing else. (Rule 3.6)
• Rule 3.7 You can notch the frame for seat clearance. (Rule 3.7)
• Rule 3.8 You can remove the transmission crossmember mounts, but no farther forward than the frame welds. (Rule 3.8)
• Rule 3.9 Behind the upper shock mounts, you can replace the rear of the frame with round, square or rectangular tubing. (Rule 3.9)
• Rule 3.3 No cutting, bending or altering the frame to change suspension brackets, except the upper control arm brackets on the front end. (Rule 3.3)
• Rule 3.4 Every frame bolt hole stays in its OEM location. (Rule 3.4)

Wheelbase, ride height and weight

• Rule 3.2, Diagram B Wheelbase: between 107 and 109 in on both sides, center of the front hub to center of the rear hub. (Rule 3.2, Diagram B)
• Rule 3.10 Frame height: no part of the frame lower than 5 in off the ground, except the front crossmember. (Rule 3.10)
• Rules 14.1, 14.2 Weight. At least 2,350 lb, weighed at the end of the event with the driver in the cockpit in full racing gear. (Rules 14.1, 14.2)
• Rules 12.11, 12.16, 14.2 With the quick-change rear end option or the any-gear-ratio option, the minimum is 2,500 lb. (Rules 12.11, 12.16, 14.2)
• Rules 11.12, 14.2 With an aftermarket transmission option (the approved list is in rule 11.12), rule 14.2 sets the minimum at 2,500 lb. Rule 11.12's words say 2,550 lb; its digits say 2,500 lb. (Rules 11.12, 14.2)

• Rule 14.3.1 Ballast. No ballast in the cockpit or outside the body or hood area. (Rule 14.3.1)

• Rule 14.3.4 Mount it to the frame or roll cage only. Never on the rear bumper, and never on a rotating or suspension part. (Rule 14.3.4)
• Rule 14.3.2 Mount it securely, paint it white and mark it clearly with the car number. (Rule 14.3.2)
• Rule 14.3.3 Use at least 2 bolts of 0.5 in to hold it on. (Rule 14.3.3)

Under the car

• Rule 1.10 No belly pans. The rulebook counts any object or material that changes the airflow under the car as a belly pan. (Rule 1.10)

Most Limited Mod bodies are fabricated sheet metal built to the measurements in this guide and hung on the frame.

The rulebook says the body has to be a 1970-or-newer American compact passenger car body, not a panel van or station wagon. (Rule 1.1)

Panel materials

• Rules 1.1, 1.2, 1.6, 1.18, 15.15 The rulebook doesn't say what metal the body panels have to be. Its body material rules, below, cover plastic, composite and aluminum. (Rules 1.1, 1.2, 1.6, 1.18, 15.15)
• Rule 1.1 No plastic or composite body panels, except the doors and rear quarter panels, which can be fire-retardant plastic or composite. (Rule 1.1)
• Rules 1.17, 1.18, 15.15 Other plastic the rules allow: the plastic nose and valances (see Nose and bumpers), plastic skirting on the nose, doors and quarter panels (see Doors and sides), plus plastic from the edge of the firewall to the body skin and from the inner wheel tubs to the body skin. (Rules 1.17, 1.18, 15.15)
• Rule 15.15 No other plastic is allowed. (Rule 15.15)
• Rules 1.2, 1.6, 1.18 Aluminum is allowed for the roof and the driver's half windshield (see Roof, windows and sail panels), and on the nose inside the bumper line (see Nose and bumpers). (Rules 1.2, 1.6, 1.18)

Damage

• Rule 1.12 Officials can keep a car with excessive body damage from racing. (Rule 1.12)

Numbers and appearance

• Rule 1.20.1 Numbers. Every car carries large, readable numbers on both sides, on the roof, on the nose and on the rear panels. (Rule 1.20.1)
• Rule 1.20.1 Side numbers. These should contrast with the body color and be at least 18 in tall and 4 in thick (the width of each stroke). (Rule 1.20.1)
• Rule 1.20.1 Roof numbers. These should be at least 24 in tall and 4 in thick. (Rule 1.20.1)
• Rule 1.20.2 Advertising. Officials can assign, approve or turn down any advertising, sponsorship or similar deal tied to an event, for the public image of the sport or of USRA. (Rule 1.20.2)
• Rule 1.20.2 Neat cars. Every car must look neat, and officials approve each car to race. By racing, you agree to follow their decisions on this. (Rule 1.20.2)