The USSA 500 Limited class is a class designed to offer the performance potential of a true racing class, with control factors in place to attempt to maintain affordability, longevity of the chassis and power plant, and rule continuity.

The 500 Limited is a regional class.The 500 Limited class is open to 500 Stock class sleds in stock trim for the 07-08 season. This will then be reviewed on an annual basis.

Chassis shall be an Open Sprint style chassis, either production or hand built.

The snowmobile must meet all applicable safety and general criteria in this section and in the general rules and regulations section of the current ISR rulebook.

Engine, Chassis, and Hood need not match.

The minimum weight shall be 350 pounds.

The maximum width is 45 inches overall.

These rules are in force for 5 years from this date, 5/8/07 Effective to 5-8-2012.

The engine must be from a stock qualified fan or liquid cooled model with a single exhaust pipe and a maximum displacement of 500 cc. Allowed modifications to the engine are listed below. No other modifications are allowed.

Engine must conform to the 15-year rule.

Air Box/air induction piping may be removed.

OEM factory wye pipe for the engine must be used.

OEM Exhaust expansion chamber must be used. Allowable modifications to the expansion chamber are as follows: After muffler/silencer canister may be removed. Exhaust stinger may be modified or changed. The expansion chamber proper must be maintained with no modifications. This is subject to the technical director’s decision and may not be appealed. Exhaust must be functionally silenced. Chassis design must accommodate the exhaust system, no changes to the exhaust system for chassis fit are allowed.

Oil injection pump may be removed.

OEM production carburetors or OEM EFI system must be used with no modifications except filed tuning components.

The OEM engine-cooling concept must be maintained.

Engine mounting plates and configuration may be modified or changed.

No additional modifications to the stock as produced engine are allowed.

OEM production ignition system must be maintained

Operating, highly visible taillight must be functional whenever the engine is running.
Drive

Any commercially available CVT type drive and or driven clutch system may be used

Diamond drive/Arctic Cat systems are legal. No lightweight components allowed.

No titanium jackshafts, axle shafts, or any other rotating component except clutch springs are allowed.

A production chaincase/ gearcase from any OEM may be used, but must be a stock production case. Chaincase cover need not be used. Chaincase may be modified to accept non OEM brake caliper.

Clutch guard must cover clutches to the centerline of clutch bolt or below. Material must be .060 inch 6061T6 aluminum or equivalent with six-inch wide belting covering the clutch guard from belly pan to running board.

Minimum of 2 inches of useable vertical travel required and must be maintained during operation.

Shock absorbers must be Fox gas charged hydraulic shocks. Shocks may be revalveable.

No external adjusters except “clicker” adjusters allowed.

No remote reservoirs allowed on ski or suspension shocks.

No air shocks/ “floats” allowed.

No electronically monitored or controlled shocks allowed.

Any shock determined to not be in “the spirit of the rule” must be removed and replaced with a conforming shock absorber. Technical inspector’s determination is final.

Carbides (one cutting edge) plus one additional edge may extend no more than 5/8 of an inch from the lowest surface of the ski. Only one (1) cutting edge per ski is permitted on independent front suspension snowmobiles. Any ski edge over ½ inch turndown constitutes a legal keel cutting edge. The ski runner, carbide edge or wear bar may be altered to a single plane angle of not less than 60 degrees inside included edge.

Shock absorbers must be FOX gas charged revalveable hydraulic shocks only.

No external adjusters except “clicker” adjusters.

No remote reservoirs allowed.

No air shocks/ “Floats” allowed.

No electronically monitored or controlled shocks allowed.

Any shock determined to not be in the “spirit of the rule” must be removed and replaced with a conforming shock absorber. The technical inspector’s determination is final.

Maximum diameter eight- (8) inch rear idler wheels.

No titanium shafts allowed anywhere in the suspension.

Suspension must use a production based slide rail.

Track must be “R” rated commercially available one-piece molded rubber track.

Minimum length is 116 inches.

Minimum width is 15 inches.

Any track wear clip combination is legal.

A rear tunnel enclosure is mandatory.

Hood must be an OEM production or OEM replica. Hood must not be modified in any manner that prevents it from being recognized as a current production model snowmobile. Colors and paint schemes are at the builder’s discretion.

No carbon fiber is allowed anywhere on the race sled.

Belly pan/lower body is at builder’s discretion.

Commercially available hydraulic brakes only. Stock OEM discs only.

No lightweight discs.

No wave discs.

Brakes may be mounted on jackshaft or front drive axle.

Liquid cooled brakes allowed.

By entering the class, the competitor agrees that any illegal chasses or engine components may be confiscated by USSA and be sold at that spring at the spring convention. Proceeds to go to point fund for the following season.
FINAL DRAFT 5-8-07