All carburetors used in competition in the NASCAR Super Truck and NASCAR Grand National Sportsman divisions must be Music City Motorplex approved. Track officials may use a carburetor provided by the manufacturer as a guide in determining whether a competitor’s carburetor conforms to the specifications set forth in the rulebook. No equipment will be considered as having been approved by reason of having passed through inspection unobserved. Any carburetor which does not conform to specifications or tolerances contained in this and/or the NASCAR rule book will not be eligible for approval and competition.   All carburetors must conform to track tech tools.

1.             ELIGIBLE CARBURETORS

1.1  ALL MCM Approved “Crate” Engines: Carburetor allowed is the approved Holley 650 cfm four barrel, model 4150 HP, sales number 0-80541-1, must

remain box stock except modifications to jets using only Holley replacement parts.  No altering or cutting will be allowed.  This rule is only effective for Grand National Sportsman and Super Trucks.  Late Models refer to section 14.

1.2  Super Truck “Machine” Engines:  May run “450” CFM following section 9 rule 1.4.

1.3  GN Sportsman “Machine” Engines: Music City Motorplex has approved the Holley “450”  two (2) barrel carburetor, following guidelines 1.4.

1.4  “450 and 500” Carburetor Guidelines:

(1)   Main Body: Reshaping, polishing, grinding, or drilling of additional holes will not be permitted.  Screw in air bleed jets will not be permitted in the 4412C main body.  Screw in air bleed jets will be permitted for the 80583-1 HP main body.  For the Holley 4412 main body the amount of holes and passages must remain as manufactured. Additional and/or plugging holes or passages will not be permitted in the Holley 80583-1 HP main body.

(2)   Choke may be removed, but all screw holes must be permanently sealed.

(3)   Choke Horn must not be removed.

(4)   Carburetor Boosters: The booster type must not be changed.  Size or shape must not be altered.  Height and location of the boosters must remain as manufactured.  All boosters must maintain an outside minimum outside diameter of 0.61 plus or minus .010 inch. The addition of material will not be permitted to the boosters with the exception of a small amount of epoxy that may be used to assist in securing the booster stem to the main body of the carburetor.  All dimensional aspects must remain as manufactured from Holley. Safety wire recommended. The hole inside the Booster may not be changed, however the feed hole may be changed.

(5)   Carburetor Venturi: The venturi area must not be altered or reshaped in any manner.  The venturi must maintain a circular (round) cross section.  The casting ring must not be removed. The location of the venturi must remain as produced by the manufacturer. Alterations that, in the judgment of Track Officials, were made to allow additional air to be picked up below the opening of the venturi such as altered gaskets, base plates, and drilling holes into the carburetor will not be permitted.

(6)  Carburetor Throttle Body: The carburetor throttle body must be used as provided by the manufacturer.  The positioning of the throttle bores in the carburetor throttle body must be the same as provided by the manufacturer.  The throttle bores must be completely round.  The throttle bores must be straight without taper from top to bottom.  The throttle bores must remain perpendicular to the top and bottom of the carburetor throttle body.  The throttle body must not be altered in shape or size.  All vacuum holes must be threaded and plugged.

(7)  Throttle Plates (butterflies):  Stock throttle plates (butterflies), for that model carburetor, may not be thinned or tapered.  Idle holes may be drilled in butterflies.  Screw ends may be cut even with the shafts, but the screw heads must remain standard as from Holley.

(8)  Transition Rings:  Transition Rings are allowed between base plate and main body on 450 carburetor only.  Base plate or main body may not be machined or beveled.

(9) Throttle Shafts:  Shafts must remain stock as manufactured and must not be thinned or cut in any manner.

(10)  Carburetor Metering Blocks: 

Grand National Sportsman & Super Trucks: Only Holley metering blocks can be used.  Surfacing of the metering blocks for improved gaskets seal will be permitted.  The only metering block permitted for the Holley 0-4412C will be the Holley, machined number 5925-sames number 134-137 or the Holley 0-80583-1HP will be the Holley machined number 12201-N-sales number 34R12203A-N.  For the approved metering blocks, the amount of holes and passages and the location must remain as manufactured with screw in emulsion bleed jet passage, however, hole sizes may be altered in the jets.  Additional holes or passages will not be permitted.

Grand National Sportsman:  Only “450” Holley, card must follow the same guidelines as above.  With no transition rings.

(11)  Accelerator Pump:  Only Holley accelerator pump discharge nozzles are allowed.  The retaining screw must not be drilled for a discharge passage.

(12)  Power Valves and Floats:  May be changed.