Suggested classes (1985 & older)
SPORT MOD 440 464cc maximum
ENGINE
1. The engine must be OEM-for-the-model.
2. Engine, engine mounts and exhaust must remain in original OEM locations for the chassis used in competition.
3. Any internal modifications allowed to the engine.
4. External modifications allowed.
5. Intake and exhaust concept must be maintained.
6. Engine bore size may be increased up to class limit (see above).
7. Aftermarket pistons allowed.
8. Intake concept must be maintained (i.e. piston port, reed valve, etc.).
9. Any round slide carburetor from a stock qualified snowmobile is allowed. Flat slide
carburetors allowed. Fuel injection not allowed.
10. Air intake silencers (air boxes) may be removed.
11. Any exhaust allowed. A commercially available silencer is required.
12. No liquid cooling allowed.
13. Must be naturally aspirated.
DRIVE
1. Any snowmobile brand OEM primary clutch allowed.
2. Any snowmobile brand OEM secondary clutch allowed. No roller secondary clutches allowed.
3. Any snowmobile brand OEM chain case.
4. Track drive shaft may be relocated
5. Any track drive shaft and track drive sprockets allowed.
6. Brake components may be replaced. Must be commercially available and not
modified.
SKI SUSPENSION AND STEERING
1. Skis must be steel or aluminum.
2. Leaf springs must be steel and functional.
3. Ski spreaders allowed. Maximum increase 3 inches (each ski).
4. No Cobra skis allowed.
5. Steering column must be OEM-for-the-model chassis. The handlebars and/or
handlebar moubting bracket may be modified or replaced.
6. Any commercially available handlebar allowed.
TRACK SUSPENSION
1. Any track suspension allowed.
TRACK AND TRACTION
1. Any commercially available one-piece molded rubber track allowed. Track must fit within the confines of the tunnel without modification to track.
2. The track must be used as produced by the molder of the track. No cutting or other modifications allowed.
FRAME AND BODY
1. Frame must be OEM-for-the-model.
2. Frame reinforcement allowed. Frame must maintain stock dimensions.
3. Hood must be OEM-for-the-model.
4. Windshield may be modified, replaced or removed.
5. Headlight may be removed.
6. Fuel tank must be OEM-for-the-model or any OEM or aftermarket replacement snowmobile tank.
7. Any seat allowed.
1. Any 1985 or older stock qualified leaf spring model allowed.
2. 1972 and 73 Chaparrals also allowed.
3. Chaparrals must maintain OEM front-end dimensions and use designated oil only
shocks (no gas shocks).
4. Approved part numbers for Chapparrals
5. On Chapparals, sway bar must be used in OEM location. A larger diameter sway bar
may be used. To mount a larger diameter sway bar, the location may be moved up
or down to clear drive.
(Please note: clutch guards and tunnel enclosures must be ISR approved)
(Please note: tunnel enclosure is mandatory)
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