MIDWEST INTERNATIONAL RACING ASSOCIATION

STOCK

PRO STOCK

SPRINT

CHAMP

Based on safety and competition – Stock snowmobiles manufactured prior to fifteen (15) years of the current model year will not be able to compete in Stock classes.

Drivers race for prize money.

STOCK FAN 600cc maximum

STOCK 500 500cc maximum

STOCK SS 600* Desiqnated models

STOCK 600 600cc maximum

Drivers race for prize money. Professional drivers are not allowed to race in the STOCK DIVISION.

PRO STOCK FAN 600cc maximum

PRO STOCK SS 600* Designated models

* In SS (Super Stock) classes, 2007 and previous 440cc models ARE allowed. See Stock rules for 4-stroke limitations.

Driver movement between STOCK and PRO STOCK divisions will be administered by the sanctioning organization. Snowmobile requirements are the same for both STOCK AND PRO STOCK divisions.

Two Stroke engines of 440 cc maximum utilizing an open chassis.

Two-stroke engines must be from a stock qualified fan or liquid cooled model with a single exhaust pipe and a maximum displacement of 600 cc in a Champ class chassis. (See rules in this section.)

Two-stroke engines must be from a stock qualified fan or liquid cooled model with a single exhaust pipe and a maximum displacement of 500 cc in a Sprint class chassis. (See rules in this section.)

1. In order to be eligible for competition, a four-stroke powered snowmobile must be classified through the ISR four- stroke classification procedure.

1. NOTICE: Effective 1 Jun 08, Radio communication is NOT allowed between crew and driver.

2. A driver and his snowmobile shall be considered a unit and once the class qualification and racing has begun, neither will be substituted until after the final race in the class.

3. The maximum number of snowmobiles allowed on the starting line for a race depends upon the width of the track at the narrowest point. There must be 5 feet of track width for each snowmobile at the narrowest point. If there are two rows of snowmobiles on the starting line, neither row may have more than the maximum number of snowmobiles allowed.

4. All Sprint races will be a minimum distance of at least three (3) complete laps.

5. A driver must always be prepared for another snowmobile to pass and must therefore be on the lookout for other snowmobiles approaching from behind.

6. Under the red, green, white, or yellow flag, drivers only may work on their snowmobiles on the course proper and must use only parts and tools carried onthe course by themselves at the beginning of the event restart

7. If two (2) or more snowmobiles do not travel fifty feet from the starting line, the race will be restarted.

1. (Mandatory in all classes except Stock where it is recommended.) The clutch cover must be separate of cowl 'configuration and cover clutches down to center of clutch bolt or below. Must be .060 inch, 6061T6 aluminum or equivalent steel material and be covered with 6 inch wide belting. Snowmobile with removable side panels may bolt clutch cover to side two panel to meet this requirement.

2. Brake control handle must remain in OEM location (left, front side). Double brake system allowed as long as it remains on the left side.

3. Brake components must be commercially available and may not be modified or altered.

1. All snowmobiles must have a minimum of two (2) inches of compression travel with the rider on the snowmobile. Travel measured at bumper.

2. Titanium suspension springs allowed in all modified classes.

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

Irregular shaped host bar carbides will not be allowed in competition for the 2009 -10 season. The use of carbide bars WITH irregular shaped host bars is under a one year notice for review of design criteria. Review in the 2010-2011 meeting

1. All snowmobiles must have a minimum of two (2) inches of compression travel with the rider on the snowmobile. Travel measured at bumper.

2. Titanium suspension springs allowed in all modified classes. Titanium springs not allowed in Stock classes unless OEM for the model.

3. Slide rail lubrication systems allowed if not in violation of local environmental laws.

1. The track studs may be no more than 3/8 inches above the track lug.

2. On one-piece molded rubber tracks: Plates welded onto track clips must be no longer or wider than track clip. Only one plate allowed per track clip. Rubber between ends of track clip may be trimmed to allow welding on stud plate.

1. Composite materials may be used only when specified.

2. (All snowmobiles in all classes). The rear of the tunnel must be enclosed with steel or aluminum comparable in strength to the tunnel material. The tunnel enclosure is required to reduce the possibility of skis and driver's extremities entering the tunnel area. The enclosure shall cover the rear and both sides and extend forward to the rear suspension mounting bolt. The bottom of the enclosure shall be no higher than one (1) inch above the center of the rear axle (with the driver in place) The rear of the enclosure shall be no further than 2.5 inches from the rear of the track. The tunnel enclosure must be securely welded, bolted, or riveted to the tunnel.

3. All casting numbers, model numbers must be left intact and affixed to the corresponding components of the engine and chassis.

4. Stirrups or foot pegs of rigid material allowed. The dimensions of the foot stirrup must not exceed the maximum width of the right-hand side of the hood nor the maximum height of the right-hand side of the hood. (Not including bumpers, skis, trim, etc.). Stirrups or pegs may be padded.

5. The color orange is not allowed on any snowmobile in Oval track racing.

6. Ballast may be used to equalize weight. Ballast must be securely contained.

1. For stock competition, a current OEM production stock qualified snowmobile tail and stoplight is required. Light must remain illuminated at all times sled is in the field of competition, whether the engine is running or not.

2. For Modified classes a taillight using an approved LED light illuminated at all times is required

3. Taillight failure during the race is not subject to disqualification.

4. Data acquisition and data acquisition systems allowed.

1. Snowmobile must comply with the GENERAL RULES AND REGULATIONS SECTION.

2. The snowmobile must have original OEM (or factory designated replacement) engine, frame, hood, and clutches supplied by the manufacturer for that particular model. All components must be OEM for the model and year, or properly filed OEM replacement parts that supersede the original OEM parts. Factory options are not allowed unless otherwise specified.

3. Any stock production 600 cc snowmobile is allowed, no special builds or 600 cc Super Stock sleds will be allowed.

4. Removal of any material from total snowmobile by means of heat, acid, drilling, grinding, sand blasting, peening, substitution, or total elimination will not be allowed unless otherwise specified in this section.

5. Stock 600 engine limitations for 4-stroke powered models.

1. No component of the engine may be altered, changed or enlarged from the engine manufacturer's original stock specifications, nor may any additional components be added to the engine. No engine kits allowed.

2. Blueprinting is not allowed. No removal of material whatsoever will be allowed. This is to include polishing, port matching, deburring, glass or sand blasting surfaces or material removal for the purposes of engine balancing or other reasons.

3. No changes in engine dimensions can be made by gasket adjustments. Gaskets may be trimmed but must remain OEM and OEM thickness.

5. Stock OEM pistons only are allowed for replacement.

6. OEM carburetor slide valve and replacement jet components without modification will be allowed in all Stock classes. No modification to carburetor body will be allowed.

7. CDI/ECU module may be reprogrammed.

8. No additional fuel pumps may be added.

9. Oil injection pump must remain in place and remain functional. Lines may be removed and plugged. Premix gasoline may be used. Stand-alone oil injection tanks may be removed.

10. Thermostats will remain in place and be functional.

11. Cooling system must remain in the OEM location except that tunnel-mounted heat exchangers may be relocated for stud clearance, but must remain within the confines of the tunnel.

12. The exhaust system must be OEM for the model and be mounted in the OEM location for the model.

13. Throttle lever may be replaced but must be thumb operated with a direct mechanical operated mechanism on rear side of right handlebar.

1. Clutches must be OEM for the model.

2. No machining, grinding, cutting or welding allowed on clutches unless otherwise specified.

3. Primary clutch - any combination of OEM for the brand, properly filed, springs, weights, and ramps may be used. Metal may be removed but not added to ramps or flyweights in the primary clutch.

4. Secondary clutch - helixes must be OEM for the brand and properly filed.

5. No machining on the clutches to accommodate springs, weights, helixes.

6. Drive chain sprockets may be changed provided that they are options filed by the manufacturer.

7. Track drive axle, track drive sprockets and non-driving wheels may not be replaced. No material substitution allowed.

8. Brake components must be OEM for the model and brand. Aftermarket pads allowed. Drive belts do not have to be OEM.

1. Ski suspension and steering must be OEM for the model unless otherwise specified.

2. Maximum ski stance is 43.5 inches measured between the ski runner cutting edges under the spindle. Ski runner cutting edges must be centered on the ski board and on the spindle.

3. The ski stance distance must be centered on the center of the tunnel.

4. Titanium springs not allowed unless OEM for the model.

5. Limiter straps allowed, but snowmobile must retain two (2) inches of vertical travel. Travel will be measured at the front and rear bumper.

6. Handlebars may be replaced, including extensions, to fit the driver. All ends must be plugged (see diagram in GENERAL COMP. SECTION). The handlebar must be of the same material with the same wall thickness (or greater) and tubing outside diameter.

1. OEM (for the brand) skis only. Must conform to General Competition Rules.

2. Reinforcement is allowed on the top of the ski board only.

3. Carbide cutting edge must be mounted in a host bar meeting current ISR rules. No more than 10 inches of cutting edge allowed.

1. Track suspension must be used as provided by OEM. Limiter straps allowed, but snowmobile must retain two (2) inches of vertical travel. Travel will be measured at the front and rear bumper. Front suspension shock spring may be modified, changed or removed. Rear suspension front shock may be removed, but if used, may not be modified or altered, and must remain in OEM mounting location.

2. Titanium springs not allowed unless OEM for the model.

1. OEM track for the model and brand must be used.

2. The track must be used as produced by the molder of the track. No cutting or other modifications allowed.

1. OEM windshields for the model only. The windshield may be altered for driver safety and comfort, but must extend five (5) inches above the highest part of the cowl. Windshield must have a safety edging. Windshield must remain in OEM mounting location. Windshields must be intact at the start of the race.

2. Fuel tank must remain OEM for the model. The fuel tank is the only tank that can be used for fuel.

3. Seat must be OEM for the brand.

4. Existing vents may be used to direct cooling to the braking mechanism. Removal of stock air vent grills including intake or exhaust is not allowed. No additional venting allowed. Protective taping or screening is restricted to the external opening only.

1. Ignition must be OEM for the year and model.

2. CDI/ECU module may be reprogrammed.

3. Fixed ignitions may be advanced or retarded a maximum of 4°.

4. No aftermarket device allowed which interrupts ignition for the purpose of launch control or traction control unless OEM for the model.

5. Headlight must be OEM for the model, and remain in place. Glass lenses must be taped.

6. OEM taillight must be illuminated at all times while on the racing surface, whether the engine is running or not.

7. Gauges-tachometers, speedometers and heat gauges may be added or removed. Openings must be closed.

1. Only single-track snowmobiles allowed.

2. Any changes or alterations allowed in the stock classes are allowed.

3. The brand of engine, hood and logo need not match.

4. All snowmobiles must comply with

GENERAL RULES AND REGULATIONS section.

5. Snowmobile must weigh a minimum of 375 pounds. No minimum combined weight of snowmobile and driver.

6. Ballast may be used to equalize weight. Ballast must be securely contained.

1. The designated engine must originate from a stock qualified 1995 or newer two cylinder snowmobile. The displacement of the stock qualified engine must be no more than 440cc (as produced and filed by the manufacturer).

2. The cylinders must be located on the engine, with the intake and exhaust ports in OEM/stock orientation to the crankcase.

3. Engine stroke may not be changed or altered.

4. Engine oil injection pump may be removed.

5. The following OEM/stock engine components may be modified, but the OEM/stock quantity of cylinders must be maintained.

a. Crankcase

b. Crankshaft - no stroke change.

c. Cylinders-may overbore not to exceed class displacement limit (440cc).

d. Cylinder heads - Spark plug quantity and location must remain OEM for the engine.

6. The following OEM/stock components may be modified or replaced.

a. Bearings

b. Connecting rods. Must maintain OEM/stock center-to-center distance.

c. Pistons

d. Rings

e. Pins

f. Gaskets

g. Intake and exhaust flanges and manifolds.

h. Rotary and reed intake valves.

i. Additional fuel pumps may be added.

j. Exhaust valves (if OEM for the model)

k. Water pump housing or cooling fan housings may be altered, removed or replaced.

I. Engine mounting plates and brackets may be altered, removed or replaced.

m.Rubber isolation mounts.

7. Mikuni VM 34 round slide carburetor only (34.1 mm maximum bore size). Only one carburetor per cylinder.

a. If the 440cc stock qualified snowmobile engine was produced with carburetors

larger than 34mm, the engine may be used with the larger carburetors only in

combination with the stock qualified chassis. The snowmobile will be allowed to

compete, but it must conform to all rules in the STOCK CLASS RULES section of Oval Sprint chapter.

b. No smooth bore, flat slide or taper bore carburetors allowed.

c. No internal changes to carburetor body allowed.

d. No modification of a carburetor bore (venturi) is allowed.

e. Outside diameter of outlet spigot may be increased. (See illustration)

f. Cut off straight portion at inlet.

g. Airbox, filter, tapered bell may be added to inlet end of carburetor.

h. Power jet carburetors and power jet carburetor kits are not allowed unless OEM for the model of engine.

i. Butterfly throttle valve carburetors are not allowed unless OEM for the model engine.

j. Larger than specified carburetors may not be downsized to meet these rules.

k. Unless otherwise specified, the only carburetor changes allowed will be replacement of tuning parts. Modifications not allowed to tuning parts.

8. No fuel injection or pressure charging is allowed.

9. The intake concept may be changed (i.e. from reed valve to rotary valve or from piston port to reed valve).

10. Intake systems that allow more than one (1) cylinder to receive intake air from a carburetor are allowed only if system is used on a stock qualified model from the same OEM manufacturer. Except for mounting, the system must be used without modification.

11. Air box may be removed or replaced.

12. OEM cooling concept must be maintained.

13. Engine torque arms, limiters, snubbers, and suppressors may be used.

14. All snowmobiles are required to have a functionally silenced exhaust system. Exhaust system must not protrude more than three (3) inches outside the hood/chassis. NOTICE: Effective 1 Jun , Additional sound level restrictions may be adopted.

1. Any commercially available drive and driven clutches and internal components may be used. Clutches and components may be modified.

2. Chain case and internal components may be altered, removed or replaced. Chains and sprockets may be altered, removed or replaced.

3. Jack shaft / track shaft may be altered, removed or replaced.

1. Front suspension components (arms, spindles, rod ends, spherical joints, the rods linkages, IFS trailing arms and radius rods) may be altered or replaced. Maximum overall width is 45 inches.

2. Front suspension springs may be altered or replaced.

3. Sway bars and links may be altered, removed or replaced.

4. Shocks and TSS struts may be altered, removed or replaced.

5. Snowmobile must maintain two (2) inches of useable vertical suspension travel.

6. Handlebars, column and controls may be altered or replaced. Aluminum handlebars allowed if produced by the OEM manufacturer.

1. Skis may be altered or replaced.

1. Track suspension may be altered or replaced.

2. Rear suspension to tunnel mounting locations is not restricted; safety and structural integrity must be maintained.

3. Snowmobile must maintain two (2) inches of useable vertical suspension travel.

1. No cleated tracks allowed. Track must be commercially available, one-piece, molded rubber track. Track must be used as produced by the molder of the track. No modification allowed unless specified.

3. Track must be "R" rated from the molder. It is recommended that the

1. Chassis/frame origination and modification are not limited or restricted. Maximum width is 45 inches.

2. Any hood allowed. May be cut out, behind the windshield for additional venting. Headlight fairing or cowling may be removed. Dash and/or console may be altered, removed or replaced.

3. Windshield not required.

4. Fuel tanks may be altered or replaced.

5. Seat may be altered or replaced.

6. No radiator may protrude from or thru the hood or chassis.

7. Heat exchangers may be mounted on the front and bottom surfaces of the belly pan if mounted flush to the pan.

1. Ignition system (CDI box, flywheel, and stator) must be OEM for the model engine. No modification allowed.

2. Ignition high-tension coil may be modified or replaced.

3. Instruments, gauges and headlights may be altered, removed or replaced.

4. An approved LED taillight must be illuminated whenever the snowmobile is on the racing surface, whether the engine is running or not.

Competition at certain tracks may be limited, restricted, or prohibited due to track and facility design.

1. Drivers and snowmobiles will be subjected to high standards of safety, construction, and driver ability. Snowmobiles and/or drivers may be restricted from competition at any time by the race/tech director without appeal.

2. Only single-track snowmobiles may compete in the 600 Open Class

3. Any changes or alterations allowed in the Stock classes are permitted in the 600 Open class.

4. The brand of engine, hood and logo need not match.

5. All snowmobiles must comply with GENERAL RULES AND REGULATIONS section.

6. Max. overall width is 45 inches.

7. Minimum weight of snowmobile powered by a two-stroke engine is 375 pounds. Minimum weight of a snowmobile powered by a designated four-stroke engine is 425 pounds.

1. The designated two-stroke engine must originate from a stock qualified 1995 or newer two (2) cylinder, two-stroke model. Four-stroke engines must originate from a stock qualified snowmobile and be designated by the ISR four-stroke classification committee.

2. Engine stroke may be changed or altered.

3. Engine oil injection pump may be removed.

4. The following OEM/stock engine components may be modified, but the OEM/stock quantity of cylinders must be maintained.

a. Crankcase

b. Crankshaft

c. Cylinders maybe over-bored not to exceed class displacement limit 600 cc for two- stroke engines or designated four-stroke displacement 1050 cc maximum.

d. Cylinder heads may be modified, changed or altered.

5. The following OEM/stock components may be modified or replaced.

a. Bearings

b. Connecting rods.

c. Pistons

d. Rings

e. Pins

f. Gaskets

g. Intake and exhaust flanges and manifolds.

h. Rotary and reed intake valves.

i. Additional fuel pumps may be added.

j. Exhaust valves on two-stroke models

k. Complete valve train and camshafts on four cycle models.

I. Water pump housing or cooling fan housings may be altered, removed or replaced.

m.Engine mounting plates and brackets may be altered, removed or replaced.

n. Rubber isolation mounts.

6. Two-stroke engines must comply with the following restriction: Mikuni VM 34 round slide carburetor only (34.1 mm maximum bore size). Only one (1) carburetor, per cylinder. Four cycle engines are limited to a maximum of 42mm. throttle body, or 38mm carburetor systems.

7. Two-stroke engines only: If the stock qualified engine was produced with larger (than 34 mm) Mikuni VM round slide carburetors, they may be used, but only on the particular model engine.

8. Two-stroke engines only: Power jet carburetors and power jet carburetor kits are not allowed unless furnished as OEM stock on the particular model engine.

9. Butterfly throttle valve carburetors are not allowed unless furnished as OEM stock on the particular model engine.

10. Two-stroke engines only: No smooth bore, flat slide or taper bore carburetors allowed.

11. Two-stroke engines only: Larger than specified carburetors may not be downsized to meet these rules.

12. Two-stroke engines only: No modification of a carburetor bore (venturi) is allowed.

13. Two-stroke engines only: Unless otherwise specified, the only carburetor changes allowed will be replacement of tuning parts. Modifications not allowed to tuning parts.

14. Any form of plenum or air box may be used.

15. Engine torque arms, limiters, snubbers, and suppressors may be used.

16. All snowmobiles are required to have a functionally silenced exhaust system. Exhaust system must not protrude more than three (3) inches outside the hood/chassis.

1. Chaincase and internal components may be altered, removed or replaced. Chains and sprockets may be altered, removed or replaced.

2. Jack shaft / track shaft may be altered, removed or replaced.

1. Front suspension components (arms, spindles, rod ends, spherical joints, the rods linkages, IFS trailing arms and radius rods) may be altered or replaced. Max. overall width is 45 inches. Minimum 3/8 inch dimension heim ends must be used on tie rods. Minimum 1/2 inch dimension heim ends must be used on all suspension articulated components.

2. Front suspension springs may be altered, removed or replaced.

3. Sway bars and links may be altered, removed or replaced.

4. Shocks and TSS struts may be altered, removed or replaced.

5. Machine must maintain two (2) inches of useable vertical suspension travel.

6. Handlebars, column and controls may be altered or replaced. Aluminum handlebars allowed.

1. Skis may be altered or replaced.

1. Track suspension may be altered, removed or replaced.

2. Rear suspension to tunnel mounting locations is not restricted; safety and structural integrity must be maintained.

3. Machine must maintain two (2) inches of useable vertical suspension travel.

1. Any commercially available track may be used.

2. No cleated tracks allowed. Track must be commercially available, one-piece, molded rubber track. Track must be used as produced by the molder of the track. No modification allowed unless specified. Minimum lug height is Y, inch.

1. Chassis/frame origination and modification are not limited or restricted. Max. width is 45 inches.

2. Fuel tanks may be altered, removed or replaced. Open class snowmobiles for Sprint competition may not carry more than 2 US gallons of fuel.

3. Seat may be altered or replaced.

4. No radiator may protrude from or thru the hood or chassis.

5. Heat exchangers may be mounted on the front and bottom surfaces of the belly panif mounted flush to the pan.

1. Ignition system type and control is open.

2. Instruments, gauges and headlights may be altered, removed or replaced.

3. An approved LED taillight must be illuminated whenever the snowmobile is on the racing surface, whether the engine is running or not.

Snowmobiles in this class must be built to resemble a Sprint or Champ snowmobile from any of the current brands. In stock and stock based classes, no change or modification is allowed unless specifically allowed by these rules. If these rules do not specifically allow a change or modification, then it must be assumed that the change or modification is not allowed. NOTICE: Rules may be frozen for 5 years starting with the 09-10 season subject to review at the 09 rules meeting.

1. Snowmobile must comply with the GENERAL RULES AND REGULATIONS.

2. The snowmobile must originate from 1989 - 1992 Polaris Indy 500 carbureted model.

3. The brand of hood, engine and logo need not match.

4. Removal of any material from total snowmobile by means of heat, acid, drilling, grinding, sand blasting, peening, substitution, or total elimination will not be allowed unless otherwise specified here.

5. Minimum weight is 400 pounds.

6. Maximum overall width of sled is 45 inches.

1. No component of the engine may be altered, changed or enlarged from the engine manufacturer's original stock specifications, nor may any additional components be added to the engine. No engine kits allowed.

2. Blueprinting is not allowed. No removal of material whatsoever allowed. This is to include polishing, port matching, deburring, glass or sand blasting surfaces or material removal for the purposes of engine balancing or other reasons.

3. No changes in engine dimensions can be made by gasket adjustments. Gaskets may be trimmed but must remain OEM and OEM thickness.

4. Maximum cylinder overbore for wear or cylinder repair cannot exceed .020 inch.

5. OEM for the model and Kimpex or SPI for the model pistons, rings and engine gaskets are allowed for replacement.

6. Replacing OEM carburetor slide valve and replacement jet components without modification allowed in FORMULA 500. No modification to carburetor body allowed.

7. No additional fuel pumps may be added.

8. Air box and oil injection system may be removed.

9. Thermostat may be removed.

10. Cooling system must remain completely stock and in the OEM location.

11. Spark plugs, spark plug wires and connectors do not have to be OEM.

12. The exhaust system must be OEM for the model and be mounted in the OEM location for the model. Welded-on after muffler and internal stinger pipe may be removed and replaced with any size stinger. The exhaust system must be functionally silenced. The ball socket on exhaust chamber may be repaired or replaced but MUST maintain original tuned length and inside diameter. NO OTHER CHANGES ALLOWED.

13. No changes or repairs allowed to "Y" pipe.

14. Engine must remain in stock location and must use stock engine plate and mounts. Torque limiters allowed.

1. Drive clutch must be P-85 Polaris.

2. Any commercially available driven clutch and internal components allowed.

3. Clutches and components may be modified.

4. Chain case, jackshaft, brake disc and track shaft must remain stock and in stock location; no modifications or lightening allowed. Chain and sprocket ratio may be changed. Belt drive system is not allowed.

5. Brake cooling duct, inside the hood, is allowed.

1. Ski suspension and steering must be OEM for the model unless otherwise specified.

2. Radius rods and tie rods may be replaced or modified.

3. Maximum outside to outside width across the skis is 45 inches.

4. Maximum total offset allowed is 1 inch, measured from the center of bulkhead. EXAMPLE: 23 inches from the center of bulkhead to the outside right

ski and 22 inches from center of bulkhead to the outside left ski = 45 inches outside ski stance with 1 inch total offset.

5. Must use all original suspension mounting points on chassis and struts.

6. May use any spring or spring adjusters. Titanium springs are not allowed.

7. POLARIS part # 7041144 is the only ski shock allowed. Shock absorbers must be OEM for the model or ISR designated replacements.

8. Sway bars may be replaced but must fit in stock location thru bulkhead.

9. Limiter strap allowed, but must maintain two and a half (2.5) inches of usable downward travel with the driver seated. Travel measured at the front bumper.

10. Suspension components may be reinforced but no geometry changes are allowed except camber.

11. The steering column and handlebars may be relocated and/or replaced. Extensions may be added to suit the driver. The lower end of the steering column must be secured with a minimum of 4 bolts. One of the 4 bolts must be in one of the OEM mounting holes. The handlebar and column material must be of same as the OEM material with the same wall thickness (or greater) and tubing outside diameter as the OEM components. The use of a universal joint is not allowed.

12. Throttle lever may be replaced but must be thumb operated with a direct mechanical operated mechanism on rear side of right handlebar.

1. OEM (for the brand) or aftermarket skis allowed. Must conform to. General Competition Rules. Ski mount on spindle may be narrowed to allow ski mounting.

2. Minimum flat length of ski bottom is 14 inches. Minimum ski width is 3 1/4 inches.

3. Reinforcement is allowed on the top of the ski board only.

4. Maximum carbide length is 6 inches per ski. Must be one, continuous cutting edge, with no other sharp edges on the ski.

1. Complete track suspension and components MUST be OEM stock for the model unless otherwise specified.

2. Track suspension must maintain a minimum of 2 inches of useable, vertical travel with the driver seated.

3. May drill new holes in tunnel or rail to change mounting locations. May not, drill excessive amount of holes, for lightening.

4. May modify or replace springs. Titanium springs are not allowed.

5. Shock absorbers must be OEM for the model or ISR designated replacements.

6. May remove front shock.

7. May relocate rear shock.

8. May change or add limiters to front and rear of track suspension. No remote limiter adjusters allowed.

9. May add or subtract marginal snow wheels and their mounts,

10. May add slide lubrication system.

1. Any commercially available 121-inch by 15 inch is allowed. Minimum track lug height is 0.50 inch,

2. The track must be used as produced by the molder of the track. No cutting or other modifications allowed.

3. No weld on hooker's plates,

4. No studs allowed directly under rails.

5. Traction products must conform to Oval Sprint requirements.

1. Must use 1989-1992 Polaris Indy 500.

2. Chassis may be reinforced.

3. May alter or replace hood, windshield, belly pan, seat, fuel tank and foot stirrups.

4. May remove bumpers, dash panels, oil tank, lights and wiring,

1. Ignition system MUST be OEM stock for this engine, no modification allowed, May not lighten flywheel.

2. Instruments, gauges and headlight may be removed.

3. Data acquisition and data acquisition systems not allowed,

4. An approved LED taillight must be illuminated whenever the snowmobile is on the racing surface, whether the engine is running or not.

The USSA / MIRA 500 Limited class offers the performance potential of a true racing snowmobile, with control factors in place to attempt to maintain afford ability, longevity of the chassis and engine, and rule continuity,

NOTICE: These rules are in force for 5 years from 1 Jun 08 to 1 Jun 13.

1. The 500 Limited class is open to 500 cc Stock Liquid and 600 cc Stock Fan class sleds in stock trim for the 09-10 season. NOTICE: This rule will be reviewed on an annual basis,

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

3. 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 Yearbook.

4. Engine, Chassis, and Hood need not match.

5. Minimum weight is 350 pounds,

6. Maximum width is 45 inches overall.

7. By entering the class, the competitor agrees that any chassis or engine components which to not comply to rules may be confiscated by the sanctioning body.

1.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,

2. Engine must conform to the 15-year rule,

3. Air Box/air induction piping may be removed.

4. OEM factory "Y"pipe for the engine must be used,

5. OEM Exhaust expansion chamber must be used. Allowable modifications to the expansion chamber are as follows:

a. After muffler/silencer canister may be removed.

b. Exhaust stinger may be modified or changed.

c. The expansion chamber proper must be maintained with no modifications, this is subject to the Technical Director's decision and may not be appealed.

d. Exhaust must be functionally silenced.

e. Chassis design must accommodate the exhaust system, no changes to the exhaust system for chassis fit are allowed.

6. Oil injection pump may be removed.

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

8. The OEM engine-cooling concept must be maintained,

9. Engine mounting plates and configuration may be modified or changed,

10. No additional modifications to the stock (as produced) engine are allowed,

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

2. No lightweight components allowed.

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

4. A chaincase/gearcase from any OEM stock qualified model may be used, (Diamond drive/Arctic Cat systems are allowed.) Chain case original origin must be declared during technical inspection if requested by technical inspector. Failure to declare will result in disqualification without appeal privileges. Chaincase may be modified to accept non OEM brake caliper.

5. Clutch guard must conform to General Oval rules for modified snowmobiles,

6. Commercially available hydraulic brakes only. Stock OEM brake discs only,

7. No lightweight brake discs.

8. No wave brake discs.

9. Brake discs may be mounted on jackshaft or front drive axle,

10. Liquid cooled brakes allowed.

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

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

3. No external adjusters except "clicker" adjusters allowed,

4. No remote reservoirs shocks allowed.

5. No air spring/ "float" shocks allowed,

6. No electronically monitored or controlled shocks allowed,

7. Any shock determined to not be in "the spirit of the rule" must be removed and replaced with a conforming shock absorber. Technical inspectors determination is final.

1. Skis and ski runners must conform to General Rules for Oval Sprint Racing.

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

2. No external adjusters except "clicker" adjusters allowed.

3. No remote reservoirs allowed.

4. No air spring! "float" shocks allowed.

5. No electronically monitored or controlled shocks allowed.

6. 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.

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

8. No titanium shafts/ titanium allowed anywhere in the suspension.

9. Suspension must use a production based slide rail. Slide rail origin must be declared when requested by the technical inspector. Failure to declare origin will result in disqualification without appeal privileges.

1. Track must be "R" rated commercially available one-piece molded rubber track.

2. Minimum length is 116 inches. Maximum is 121 inches.

3. Minimum width is 15 inches.

4. Any track wear clip combination is legal.

1. A rear tunnel enclosure is mandatory.

2. 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.

3. No carbon fiber is allowed anywhere on the snowmobile.

4. Any belly pan/lower body allowed.

1. Ignition system must be OEM for the model engine.

2. An approved LED taillight must be illuminated whenever the snowmobile is on the racing surface, whether the engine is running or not.