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IMCA Hobby Stock
2013 Hobby Stock Revised November, 2010. Revisions/clarifications underlined, recommendations italicized. The rules and/or regulations set forth herein are designed to provide for the orderly conduct of racing events and to establish minimum acceptable requirements for such events. These rules shall govern the condition of all events, and by participating in these events, all participants are deemed to have complied with these rules. NO EXPRESSED OR IMPLIED WARRANTY OF SAFETY SHALL RESULT FROM PUBLICATIONS OF OR COMPLIANCE WITH THESE RULES AND/OR REGULATIONS. They are intended as a guide for the conduct of the sport and are in no way a guarantee against injury or death to a participant, spectator or official. The race director shall be empowered to permit reasonable and appropriate deviation from any of the specifications herein or impose any further restrictions that in his opinion do not alter the minimum acceptable requirements. NO EXPRESSED OR IMPLIED WARRANTY OF SAFETY SHALL RESULT FROM SUCH ALTERATION OF SPECIFICATIONS. Any interpretation or deviation of these rules is left to the discretion of the officials. Their decision is final. 2011 Hobby Stock - No one with an IMCA license during the same calendar year in any other division may compete in this division, except: licensed SportMod™ drivers (must still purchase Hobby Stock license). Unless otherwise noted, all parts to be approved OEM and must match make and year of car. 1. SAFETY EQUIPMENT: Rules apply at all times car is on track. Snell-rated SA2000, SA2005 or SA2010 helmet required. Roll bar padding required in driver compartment (Fire retardant recommended). SFI-approved full fire suit required. Fire retardant gloves, shoes and neck brace (or head and neck restraint) required. Right and left seat head supports required if using head restraint system with no neck collar. Recommended: Fire retardant head sock and underwear; collapsible steering shaft. Driver-side window net required, minimum 16 inch by 20 inch ribbon or mesh style, and must be mounted to roll cage so latch is at top front of window. Minimum three inch (two-inch with head restraint system) wide SFI-approved five point safety belt assembly required (Y-type shoulder harness not allowed), must be mounted securely to roll cage, recommended to be no more than two years old. Kill switch required within easy reach of driver and must be clearly marked ‘OFF’ and ‘ON’. 2. FRAME: Any American OEM full body rear wheel drive passenger car, 1964 or newer, full frame or unibody. Frame must match body. Minimum 107.5 inch wheelbase, maximum one inch difference from side to side. Rear of frame behind rear tires, no further forward than one inch behind factory seam, may be replaced in OEM location with two inch by three inch steel tubing with minimum 0.095 inch wall thickness, same length as material removed. Factory seam must remain visible. Unibodies must tie rear frame to front frame. Frames may be “X” braced. No Station Wagons, Camaros, Firebirds, or Mustangs. 3. ROLL CAGE: Main cage must consist of continuous hoops, minimum 1.75 inch O.D. tubing, with wall thickness of at least 0.095 inch, low carbon or mild steel recommended. Four-post roll cage required, front down bars and rear hoop must be welded to OEM frame. Driver’s head must not protrude outside cage with helmet on. Rear hoop must have “X” brace, consisting of one full horizontal and one full diagonal bar, minimum 1.25 inch O.D. with 0.083 inch wall thickness. Front down bars must be tied together, passenger side front down bars must be maximum 11 inches in from top of door. Must be minimum 40 inches between front and rear down bars at top of door panel. Maximum 41 inches from top center of windshield to front edge of rear hoop; maximum 13 inches to front edge of top halo. Top halo must be minimum 40 inches across, outside to outside. Rear hoop may be maximum 12 inches in from bottom of opera window. Minimum one cross bar in top halo. May have maximum two horizontal bars, (in addition to bar tying front frame horns together) for radiator protection; must be behind bumper, within confines of body, no wider than OEM frame horns. Rear kickers (down bars) and engine hoop required, and must be minimum 1.25 inch O.D. tubing with 0.083 inch wall thickness. Fuel cell protection required, must be mounted frame rail to frame rail, no higher than fuel cell, inside trunk area with maximum 1.75 inch O.D. tubing. All bars must be inside body. 4. DOOR BARS: All door bars and uprights must be minimum 1.75 inch O.D. with 0.095 inch wall thickness. Minimum three door bars, both sides, parallel to ground, and perpendicular to driver. Minimum four uprights tied from frame to top door bar on driver side, and minimum three uprights on passenger side. Steel door plates, 18 gauge or 0.049 inch minimum thickness, must be securely welded to outside of door bars on driver’s side. Plate must cover area from top door bar to rocker panel and from rear down post to five inches in front of seat. Must be visible for inspection. 5. BODY: All bodies must be unaltered OEM, or OEM replacement, in OEM location and match frame. Front body mounts must be visible. Sunroofs and T-tops must be enclosed. Aftermarket plastic nose piece allowed, recommended to match body. No spoilers, hood scoops, ground effects or skirting altering OEM appearance. OEM STEEL hood only, hood may be gutted. OEM STEEL trunk lid only, no gutting. Hood and trunk must be securely fastened and back of hood must be sealed off from driver compartment with metal. Hood must be separate from fenders. Front inner wheel wells may be removed, rear wheel wells may be removed to middle seam. Trunk floor directly over rear end housing must be removed. No overlapping or shortening of body panels. All glass must be removed, all windows in body must remain open; maximum seven inch metal sun visor allowed across top of windshield opening. All doors must be securely fastened. Fenders and quarter panels may be trimmed for tire clearance, ONLY. No reflective body panels. Car number must be minimum four inches thick and 20 inches tall and clearly visible, on both sides, top and back of car, and front, if possible. 6. DRIVER COMPARTMENT: Minimum three windshield bars in front of driver. Aluminum high-back seat only and must be bolted in, using minimum 0.375 inch bolts. Driver seat may be no further back than rear edge of B-pillar. Driver must be sealed off from track, driveline, engine and fuel cell. Dash not to extend more than 24 inches back from center of lower windshield opening. Dash must be flat, rear can be no higher than front, except for cowl in front of driver. No other interior tin or covers. Inside rear quarter panels, below window level, may be cut out. Doors may be gutted. No cutting out of firewalls, roof, floor, kick panels, rocker panels, except for roll cage clearance. All holes in firewalls and floor must be covered with metal. Rear firewall and speaker deck must be metal and be of OEM design for that make and model. No mirrors of any kind. 7. FRONT SUSPENSION: All components and mounts must be steel, unaltered OEM, in OEM location and match frame. OEM rubber A-frame bushings only. No aftermarket ball joints. No sway bars, spring spacers, chains or cables. Exceptions are: for 1978-1987 GM mid-sized metric frame, OEM upper A-frame may be replaced using aftermarket upper A-frame (steel or aluminum cross shaft allowed), must display “IMCA approved” decal on top of rear tube of A-frame; bolt on spindle savers allowed. Upper A-frame mount must remain OEM and cannot be moved. 8. STEERING: All components must be steel unaltered OEM, in OEM location and match frame. OEM steering column may be replaced with steel steering shafts (collapsible steering shaft recommended). Steel knuckles only. No steering quickeners, or remote power steering reservoirs. Steering wheel and quick release (required) may be aluminum. 9. SHOCKS: One unaltered steel, nonadjustable, OEM-mount shock, in OEM location, per wheel. No coil-over shocks, air shocks, remote reservoir shocks. No Schrader or bladder type valve allowed. No coil-over eliminators. Rear OEM shock location is 4.5 inches from bottom of housing to center of bolt hole, and centered on control arm bracket. $50 claim on any shock. One or all shocks on car may be claimed per event, counting as one claim on card, following shock claim procedures and penalties (Refer to www.imca.com). 10. SPRINGS: One steel spring per wheel only in OEM location. All coil springs must be minimum 4.5 inches O.D. and non-progressive. No spring rubbers allowed. 11. REAR SUSPENSION: All components and mounts must be steel, unaltered, OEM, in OEM location and match frame. OEM rubber control arm bushings only. Center of rear lower control arm bolt hole must be 2.25 to 2.5 inches from bottom of housing. No independent rear suspension. No sway bars, panhard bars, spring spacers, extensions, chains or cables. 12. REAR END: No floater rear ends. OEM, or OEM replacement (recommended) solid steel axles only. Nine inch Ford rear end allowed, but must be mounted like OEM rear end (centered) for that make and model. One inch inspection hole in housing required. No lightened ring gears. Must be welded spider gears, or mini spool. No torque dividing differentials. 13. BUMPERS/RUB RAILS: REAR bumper must be OEM in OEM location, capped to body with steel, welded or bolted. Maximum one inch wide by two inch tall steel or lexan rub rails allowed – bolted flush to body. Front and rear tow hooks mandatory. No sharp edges allowed on bumpers, rub rails or bolts. No bars past outside edge of body other than rub rails. All front bumpers must be mounted minimum six inches from front frame horns. Steel bumper mounts only. One of two FRONT bumper options must be used and must be OEM height: OEM: Bumpers not covered by plastic nose must be complete, unaltered OEM, capped to fender with steel, welded or bolted. Aftermarket: Fabricated tubular bumpers allowed, but must be covered by plastic nose and bent to fit with rounded ends. Main bumper bar must be minimum 1.5 inch O.D. (maximum two inch) with 0.083 inch (maximum 0.125 inch) wall thickness. 14. TIRES/WHEELS: Unaltered OEM 205/75, or 205/70, 14 inch or 15 inch passenger car tires only. All four tires and wheels must be same size. Tires must be inside body. No racing, snow, or all-terrain tires. No softening, conditioning, siping/grinding or grooving (Refer to www.imca.com for automatic penalties). Maximum seven inch wide, three to four inch offset, unaltered, D.O.T.-stamped steel wheels with standard bead bump – must weigh minimum 21 pounds. No wheel spacers. One inch O.D. steel lug nuts required. No bleeder valves. 15. BRAKES: Steel, unaltered OEM, or unaltered OEM replacement, operative four wheel, disc (front) and drum (rear) brakes, must match frame or rear end. Full OEM backing plates, no aftermarket. Master cylinder must be in OEM location. No antilock brake systems. No aftermarket brake pedal assemblies, brake shut-off or bias adjuster. Steel brake lines only, must be visible. No oil bath front hubs. Hubs/rotors, axle flanges and drums may be changed to different bolt pattern and larger studs. 16. EXHAUST: OEM cast iron exhaust manifolds only. No center dump type manifolds. Exhaust must extend past firewall and turn towards ground. Maximum two inch O.D. exhaust pipes. Must remain dual exhaust, no crossover or ‘Y’ pipes. No exhaust sensors. Mufflers recommended. 17. FUEL SYSTEM: Racing fuel cell required, maximum 22 gallon capacity (12 gallon recommended), must be in minimum 20 gauge steel container. Must be securely fastened in trunk above level of OEM trunk floor, behind rear tires, no further forward than factory seam where rear frame rail can be replaced, with minimum two solid steel straps around entire cell, two inches wide and .125 inch thick. No fuel cells allowed over rear end housing. Metal firewall must be between driver and fuel cell. All cell mounts must be steel, securely welded to frame/cage. No adjustable fuel cell mounts. Fuel cell vents, including cap vent, must have check valves. If fuel cell does not have aircraft style positive seal filler neck/cap system – a flapper, spring or ball type filler rollover valve is required. Fuel lines through driver compartment must run through metal pipe or metal conduit. One fuel filter allowed, cannot be in driver’s compartment. No cool cans. Air cleaner top/stud cannot direct air into carburetor. No top flow air cleaner housings, cold air boxes or air cleaner ductwork. Mechanical OEM type push rod fuel pumps only. CLAIM ENGINE: must use unaltered OEM two barrel carburetor for that engine, except: booster I.D. may be machined to 0.25 inch, venturi I.D. machined to 1.375 inch and throttle bore I.D machined to 1.6875 inch on Rochester carburetor. 0.625 inch minimum booster height on Rochester carburetor. Must remove carburetor choke plate. No carburetor spacers on claim engine. One 0.25 inch (maximum) thickness gasket only. GM CRATE ENGINE: must use GM two barrel Rochester carburetor and IMCA required carburetor adaptor – Speedway Motors, part # 135-3502G. Maximum of two 0.100 inch thick carburetor gaskets only. $50 cash claim on ALL carburetors, following carburetor claim procedures and penalties (Refer to www.imca.com). 18. FUEL: Gasoline only. Racing fuel allowed. No E85. No performance enhancing or scented additives. Fuel must pass both dielectric meter and chemical tests (Refer to www.imca.com for automatic penalties). 19. WEIGHT: No ballast allowed. Any item deemed as ballast will be required to be replaced – i.e. fuel cell straps, fuel cell cans, battery boxes, etc. No titanium, magnesium or carbon fiber products. No gun-drilled, tubular, hollow bolts or studs. Steel fasteners only. 20. BATTERY/STARTER: One 12 volt passenger car battery only, must be securely mounted between and above frame rails, and positive terminal must be covered. Battery must be in Marine type case if mounted in driver compartment. Starter must bolt in OEM location. Car must have capability of starting without being pushed or pulled. Car must leave initial staging area on demand, unaided, or go to rear of that race. 21. GAUGES/ELECTRONICS: No unapproved cameras, transmitting or listening devices (exception is one-way RACEceiver radio by officials), timing retard controls, or digital gauges (including tach). No electronic monitoring computer devices capable of storing or transmitting information except memory recall analog tach. 12 volt ignition system and OEM HEI distributor only. Ford/Chrysler may use HEI distributor. No billet housings or crank triggers. Ignition rotor, cap, coil and module must remain OEM-appearing. Crate engine MUST use original HEI distributor with MSD #8728 rev-control and 6,200 rpm chip. Claim engine MAY use MSD #8728 rev-control with any rpm chip. Rev-control must be out of reach of driver, but accessible for inspection. No ignition boxes. All wiring must be visible for inspection. OEM type alternator with internal regulator allowed. No electronic traction control devices (Refer to www.imca.com for automatic penalties). 22. TRANSMISSION/DRIVE SHAFT: All forward and reverse gears must be operational. Manual: Must be unaltered OEM three or four speed, with minimum 10.5 inch steel/organic single disc-type clutch and steel pressure plate assembly inside an explosion-proof steel bellhousing – minimum 270 degrees around top of clutch and flywheel area. No lightweight bellhousings. No hydraulic clutch release bearing. Steel unaltered flywheel only – 16 pound minimum – $150 fine if illegal. Automatic: Must be unaltered OEM, with unaltered OEM pump, original bellhousing and minimum 10 inch diameter torque converter containing a minimum of three quarts of fluid – $150 fine if illegal. Torque converter must have a minimum 0.125 inch plug. Must have approved scatter shield constructed of minimum 0.125 inch by three inch steel, 270 degrees around flexplate. Flexplate must be full, unaltered OEM, or OEM replacement. No manual bump starts allowed. Drive shaft: Steel drive shaft (minimum 2.5 inch diameter) and slip-yokes only. Drive shaft must be painted white. 360-degree driveshaft loop required and must be constructed of minimum 0.25 inch by two inch solid steel, or one inch tubing, mounted six inches back from front U-joint. 23. ENGINE COMPARTMENT: Engine must be in OEM location. On GM metric frame, center of fuel pump must be located minimum 1.75 inches in front of cross member (measured at frame). Ford metric frames must have back of fuel pump in front of cross member. Frame and cross member may not be altered for engine placement. Engine mount holes cannot be removed or altered on block. Aftermarket steel engine mounts allowed. No mid-plate allowed. Engine must be OEM appearing, must be able to be used in conventional passenger car without alteration. GM with GM, Ford with Ford, Chrysler with Chrysler. Minimum two-core radiator, must be mounted in front of engine. Overflow tubes must be directed to ground. Steel or aluminum V-belt pulleys only. No electric fans. 24. ENGINE OPTIONS AND SPECIFICATIONS: All cars must clearly display on driver side front roof post which engine they are competing with. Must be contrasting in color from body, minimum two inches tall and display CLAIM or CRATE. Markers not acceptable. (A) CRATE ENGINE: Must use unaltered sealed GM #88958602 or #19258602 crate engine. Upon inspection, any different, altered or missing GM seal bolts will result in disqualification, loss of all IMCA points for the season, $1,000 fine and one year suspension. GM seal bolt exception is IMCA approved and issued cable-lock rebuild system, and oil pan may be replaced by IMCA certified repair center with Kevko pan #1087NRHw/ISP and Kevko pick-up #1003-1 3/4. $250 fine for any crate engine not using required spacer, distributor, rev limiter, pushrods, valve springs or rocker arms. Any driver using crate engine cannot claim engine or have engine claimed. During same season, no driver is allowed to claim an engine after competing with a crate. If a driver switches to a crate after claiming an engine, the crate engine is then claimable. (B) CLAIM ENGINE: Any American make engine allowed. BLOCK: OEM steel passenger vehicle production block only. No GM Bowtie, Ford SVO or Chrysler W components allowed. GM approved block numbers are: 3892657, 3914660, 3914678, 3932388, 3932386, 3956618, 3970000, 3970006, 3970010, 3970014, 10066033, 10066036, 10243880, 14010207, 14010209, 14010287, 14016376, 14016379, 10054727, 14088528, 14088548, 14088552, 14093638, 14101148. Stroke must match block. No 400 or larger cubic inch parts allowed. Maximum 361 cubic inches (GM); 363 (Ford); 370 (Chrysler). Violation of cubic inch limit must be verified by removal of head and will result in disqualification, loss of all IMCA points for the season, $1,000 fine and a 30-day suspension. Maximum compression ratio is 9.0 to 1, no tolerance. Compression ratio checked using Whistler and cubic inches checked using pump, OR by visual inspection of part and/or casting numbers, pistons, etc (track option which method is used). Flat top or dish pistons only, no gas ported pistons. OEM or OEM replacement steel crankshaft only – cannot be lightened. No aerowing, bullnose, knife edge, undercut or drilling of second or third rod throws. OEM or OEM replacement steel rods only – GM 5.7 or 6-inch rod allowed. Cap screws allowed. Conventional flat tappet cam/lifters only, cannot alter lifter bores. OEM firing order cannot be changed (GM: 1-8-4-3-6-5-7-2). May use oil restrictors. ‘Wet’ sump oiling system only. Steel oil pans only. Racing oil pans allowed. Mandatory one inch inspection hole in all pans – no obstructions to crank and rods. Accumulator allowed, must be mounted under hood. CYLINDER HEADS: Steel only. Must be unaltered approved OEM and minimum 76 cc combustion chamber. Only GM OEM approved head numbers are: 14079267, 3986336, 3986339, 3986339X, 3986388, 3932441, 376445, 3928454, 3932454, 3876487, 3973487, 3973487X, 3973493, 3951598, 468642, 330862, 333882, 3998920, 3998991, 3998993, 3998997, 3970126. Maximum size valves on these heads are 2.02 inch intake and 1.60 inch exhaust. May use Engine Quest (EQ) Stock Replacement (SR) cylinder head, part number CH350I, head must remain as produced, seat angles and valve sizes can not be changed: three angle valve job only (absolutely no casting removal in valve pocket of EQ head, for any reason); Ford – no after market or SVO heads; Chrysler – no after market or W-2 heads, 360 cubic inch heads only. No porting, polishing or alterations of any kind to heads or intake, disqualification and $250 fine if illegal. OEM non-roller rocker arms only. GM – 1.250 inch maximum O.D. valve spring, no beehive valve springs allowed. Guide plates and screw-in shouldered studs (0.375 inch max) allowed. No stud girdles. Poly locks allowed. INTAKE: Must use unaltered OEM cast iron two barrel intake. No hi-rise or marine intake manifolds. Unaltered OEM type harmonic balancer only. OEM type steel or aluminum water pumps only. 25. ENGINE CLAIM: Refer to www.imca.com for claim eligibility requirements. (A) $550 cash claim on engine, $25 goes to wrecker for pulling engine and $25 goes to official. (B) Claim does not include – 1. flywheel, 2. clutch, 3. pressure plate, 4. bellhousing, 5. breathers, 6. carburetor, 7. starter, 8. motor mounts, 9. oil/temp. sending units, 10. fan and pulleys, 11. clutch ball, 12. clutch arm, 13. throw out bearing, 14. dip stick, 15. water pump, 16. fuel pump, rod and plate, 17. distributor, 18. plug wires, 19. water outlet and restrictor. 20. exhaust manifold and pipes. NOTE: During engine claim, block and head numbers should be verified, heads, intake, connecting rods and crankshaft should be visually inspected, exhaust manifold must be removed to inspect heads, and one spark plug must be removed to check flat top or dish pistons prior to transfer of engine to claiming driver. If, at this time, engine is found illegal, claimed driver is disqualified and suspended from all IMCA sanctioned events until such time as a $250 fine is paid, for first offense, second offense penalties will be $500 fine and/or suspension. Claimer then has option to accept or decline engine – if declined, driver is not charged with claim. 26. POINT STRUCTURE/PROCEDURES: Refer to www.imca.com. 27. EIRI: (Except in rare instances) Decisions of officials are final and binding without exception. In some cases, track safety rules may take precedence over IMCA rules – any discrepancy between IMCA and track rules should be brought to the attention of IMCA. Any rule changes or clarifications during the course of the year will be amended at www.imca.com as well as published in Inside IMCA, the official newsletter of IMCA, and will be considered as an official part of rules. For more information, call Tom Gutowski at 402-350-6120, or Kirk Niehouse at 515-231-9757 . Copyright © 2011 IMCA. All rights reserved. No part of this publication may be reproduced, stored, or transmitted in any form, without prior written permission.