Hootenanny X275 Radial Rules

X275 is a heads-up class designed for small tire, single power adder small block and big block engine combinations to compete on the eighth mile. Centrifugal Superchargers, Turbochargers and Nitrous Combinations are restricted to specific dimensions/sizes to ensure overall class parity. All entries have the option to run either a 275 or 28 x 10 drag radial tire or 28inch by 10.6inch bias slick on any type of rear suspension.

Note: This set of class rules is presented to all competitors under the assumption that any modifications not specifically written within these rules shall be deemed illegal, unless the competitor has the expressed written consent from the Event Tech Director. All parts and assemblies subject to tech inspection.

This class will be a 16 or 32 car field, heads-up – Pro Style Ladder on a .400 Pro Tree


6 Cylinder diesel (Cummins) Turbo 88mm 431 3200 85 mm 3125

6 Cylinder/4 Cylinder Turbo up to 88mm 431 2825 Turbo +25 for auto w/NOS

Small Block Nitrous 500 cu in 2325 (+25lbs. inline non SVA +50 non-inline /any intake/carb)(nothing lighter than 2300 lbs. regardless of deductions)(+25 lbs. for 10.2 deck height)

Small Block Supercharger max 4.025” Inlet 480 cu in 2875 non-inline and 2800 inline (6 cyl deduct 150 lbs. no other deducts for cubic inch permitted)

Small Block Supercharger max 4.200”Inlet and 4.025 Inlet “R” model 480 cu in 2950 non-inline and 2875 inline (6 cyl deduct 150 lbs. no other deducts for cubic inch permitted.)

Small Block Roots Supercharger 871 (on M1 with billet head or block) 2925

Small Block Turbo 80mm 480 2800 base

Small Block Turbo 85mm 480 3050 base (+25 for Q16/E85/C85)

Small Block Turbo 88mm 480 3100 base (+25 for Q16/E85/C85)

Big Block Naturally Aspirated 750 2600

Buick, Olds, Pontiac – 550 cu in Nitrous w/any intake 2700 lbs.

Big Block Conventional Head Nitrous up to 588 2725

Big Block Un-Conventional Head Nitrous up to 588 2800

Big Block Conventional Head Nitrous 589-610 2775

Big Block Conventional Head Nitrous 611 to 650 2800

Big Block Un-Conventional Head Nitrous up to 650 2850

Base weights are set with gasoline as fuel (see notes)


Maximum CID for all small block boosted entries is 480 inches.

Maximum CID for all small block nitrous entries is 500 inches.

Maximum CID for 4.84/4.90 nitrous big block entries is 650 inches (add 2.5lbs per cubic inch over 632 for nitrous combos)

Maximum Deck Height for all boosted/blown small block combinations is 10.000 inches.

Maximum Deck Height for nitrous small block & GM Big Block combinations is 10.200 inches.

Maximum Deck Height for Ford Big Block Combinations is 10.300 inches.

Maximum Deck Height for Mopar Big Block Combinations is 10.700 inches.

6cyl/4cyl combinations are permitted intercooler and Nitrous with gasoline as fuel.

(Prohibited with M1 as fuel unless using auto trans)

Boosted diesel combinations may only use nitrous oxide as a second power adder. (jet limit TBD)


Add 50lbs for M1 with Turbocharger (intercooler not permitted with M1)

Add 50lbs for M1 with Supercharger (intercooler not permitted with M1)

Add 50lbs for BB NOS using lock up transmission and/or converter (no add for NA or SB NOS)

Add 75lbs for cast/cast boosted with lock up

Add 150 lbs for turbo or supercharger with billet head or block)(25lbs. for SVA Turbo combinations) for any combination using a lockup transmission/convertor.

Add 50 lbs. for Inline 6 with 5 speed/clutch or lock up

Add 50lbs. for billet head (must be used with cast block only of stock bore space all combinations)

Add 50lbs. for billet block includes coyote (must be used with cast head only and be stock bore space all combinations)

Add 25lbs. for SR20 or equivalent BB cylinder head must maintain 20 deg. Valve Angle and conventional port layout

Add 50lbs. for any Hemi Style Head

Add 25lbs. for any exducer tip to tip measurement larger than 134mm

Add 25lbs for 4 link rear suspension – * see rear suspension notes

Deduct 25lbs for any SB Nitrous combination using inline non-stock valve angle 12deg to 18deg cylinder head.

Deduct 50lbs. for blower/boosted with mass produced cast carb type intake.

Deduct 50lbs for cast iron small block Chevrolet 9.025 or LS w/ iron block

Deduct 50lbs. for turbo without ram-air

Deduct 50lbs for IRS

Deduct 50lbs for belt driven centrifugal supercharger.

Deduct 50lbs. 3.70 inducer diameter centrifugal supercharger (from 4.025 base weight)

Deduct 50lbs for NA/SB NOS combinations using a 4150 carb/throttle body/25lbs deduct for boosted combo

Deduct 50lbs for any SB Nitrous combination using RR Stock Valve Angle (23*GM, 20* Ford, 18* Mopar, or any square port 15*LS)

Deduct 50lbs for any SB boosted combination using inline 11deg or down cast cylinder heads (unless sub 365 cu inch -25)

Deduct 75lbs for any SB boosted combinations using 12deg to 15deg inline square port heads or Stock Valve Angle (23* GM, 20* Ford, 18* Mopar) Raised Runner Heads (unless sub 365 cu in – 50lbs)

Deduct 100lbs. 4.10 inducer diameter centrifugal supercharger (from 4.200 base weight)

Deduct 75 lbs. PTE 85/88 Gen II PM (must have 133 mm tip to tip and 133 mm backing plate)

Deduct 125lbs. GTX55-85 GTX55-88 GEN 1 (118 mm compressor exducer back-plate)

Deduct 50lbs. any non spray bar plate nitrous system

Deduct 100 lbs. for standard bar type plate

Deduct 100lbs. SB Nitrous and SB boosted entries using cathedral port LS – 13.5/15 degree or Stock Valve Angle 23*GM, 20*Ford, or 18*Mopar non raised runner inline valve heads.

Deduct 175lbs for any cast Ford Modular engine combinations or cast 8.2 deck height combinations

Deduct 150lbs for any 365 Cubic inch or smaller pushrod combinations (3.8L 4.1L and 4.3L V6 will deduct from Inline 6 88 mm base weights)





Any aftermarket cast iron or aluminum engine block permitted. Billet engine blocks are permitted. Billet blocks are only permitted to be used with cast cylinder heads. The use of billet cylinder heads on billet blocks is prohibited. Factory OEM bore spacing for particular engine brand being used is required for all entries. Diesel combo exempt.


SFI Spec 18.1 balancer is required.


Engine block and cylinder heads cannot be in contact with the firewall.


Any aftermarket cylinder head is permitted. Small block entries are permitted to use billet cylinder heads. Billet cylinder heads are only permitted to be used with cast engine blocks. The use of billet cylinder heads with billet blocks is prohibited. Big block entries are permitted to run any cast conventional and unconventional style heads with prior tech approval. Twin spark plugs per cylinder are permitted for Factory OEM applications (Gen III Hemi). Diesel combo exempt.


Any intake manifold is permitted. Except on Big Block conventional or Big Block unconventional stock bore space, nitrous combos, these combos will only be permitted a single opening intake manifold out of any material.


I6 entry with automatic transmission limited to single entry nozzle at inlet of intake/throttle body.

Small Block Entries: Allowed to use any multi-stage system.

Big Block Entries: Allowed to use any single-stage system with a maximum of one nozzle per intake runner.

Big Block & Small block nitrous are permitted water/meth injection. All EFI Big Blocks will only be allowed 2 nitrous solenoids for a dry nitrous system and will only have 1 line per nozzle/per cylinder. (Using both sides of the fogger nozzle on a dry EFI NOS BB combo is prohibited (Cold nitrous ok)


All air must enter through the inducer minor – I.E. the smallest inlet dimensions called out in the rules. Applies to forward facing map grooves that must be 90*. Any other means of air entry into the turbo or supercharger not permitted.


Centrifugal superchargers are allowed a maximum impeller inducer diameter of 4.200 inches with a maximum exducer outside diameter of 6.00 inches (factory dimensions). Supercharger impeller must only be constructed of cast or billet aluminum. Supercharger is permitted a fresh air source from either the front bumper or grille area of the vehicle. Factory dimensions only for F3D-102/F3D-106 and V30-102/V30-105


Single turbocharger limited to 88mm maximum. *Garrett GTX GEN II/PTE XPR/GENX (using current X275 exhaust/turbine measurements). Turbocharger size will be verified by measuring the housing bore at the leading edge of the impeller wheel and must maintain the contour of the compressor housing. (Stepped compressor wheel prohibited) Inducer minor dimensions may not exceed 80.9/85.9mm/88.9mm and Exducer backing plate and blade tip to tip dimensions may not exceed 133mm on MID FRAME turbos except where noted. *The Garrett GTX GEN II/PTE XPR Inducer dimensions may not exceed 85.9mm/88.9mm, Exducer backing plate dimensions may not exceed 133mm. The Exducer tip to tip major diameter may not exceed 142.5mm. On mid-frame turbo claiming 85.9/88.9 on tip to tip inducer measurements the inspection tool must capture .200 of the blade tip to be eligible for the latest deductions in weight. (Tech insp. discretion) On LARGE FRAME turbos the inducer may not exceed 85.9/88.9mm and Exducer major dimensions may not exceed 141.224mm. The maximum diameter of the housing bore at the leading edge of the wheel may not exceed 2 mm more than the maximum allowable turbocharger size permitted. Inserts or reducers to achieve inlet or outlet dimensions prohibited. Compressor map groove will not exceed .250 of an inch and must be maintained throughout the entire circumference of the groove. Adjustable map groove rings prohibited. Any turbocharger entry may be asked to remove the compressor cover and/or turbine housing for inspection. The turbine wheel may not exceed 113mm X 103mm on ANY turbocharger. Turbine wheels are only allowed to be constructed of Inconel material. Billet aluminum compressor wheel/impeller permitted. Any inconsistent modifications to compressor or turbine wheel, blades, hubs, cover, or housing, beyond accepted commercially available manufacturing process, is PROHIBITED. No reduction or milling permitted on the compressor or turbine retention nuts. (hub and turbine retention nut diameter minimum is .850) No bore-less shaft turbochargers permitted. Welded covers not permitted on any 80/85/88 or any other size permitted in X275. Cover revision from March 2020 applies. Please note all turbos will have a cast 1 piece cover. No inserts, welding, or two piece covers permitted. Compressor housing and inlets must be manufactured solely from a single continuous casting. Any turbo not meeting this criteria will be deemed illegal and will not be permitted to compete in X275.


All boosted gasoline, diesel or E85 entries are permitted to use one intercooler. Intercoolers can either be air-to-air or air-to-water. Water and/or ice are the only agents allowed to be used with intercoolers. The use of any other agent to assist in the cooling of discharge and/or inlet air for boosted applications is prohibited. Use of intercooler with M1 (Alcohol) is prohibited (except on 6cyl/4cyl with M1 or Factory intercooled V8 and automatic trans).


Meth injection permitted. The use of a single nozzle/injector in any engine combination forward of throttle body/carburetor in the charge tube is permitted but must be within 6 inches of throttle body or carburetor and must supplied fuel directly from intake mounted fuel rail (diesel combo permitted stand-alone fuel supply).


All entries are required to have an oil retention device. The device can either be a custom built ballistic blanket or a ‘’belly’’ style pan.


Any cooling system permitted. Radiators are not required.


Any exhaust system permitted. Exhaust may exit underneath car or out the front fenders but must not affect timing or staging beams.


Any electronic, mechanical or belt driven fuel pumps are allowed. Electronic fuel pumps must shut off with the master electric cut-off switch. Fuel cell must have a pressure cap and be vented to the outside of the body. Front mounted fuel cells must meet SFI Spec 28.1 and be mounted between the frame rails or enclosed in a round tube frame. A round tube frame must be constructed of a minimum of 1 ¼-inch O.D. x .065-inch chrome moly tubing. Artificial cooling or heating of fuel (i.e., cool cans, ice, Freon, etc.) prohibited. Circulating systems that are not part of the normal fuel pump system are prohibited.


Any aftermarket electronic or mechanical fuel injection may be used.


Any aftermarket throttle body permitted. Nitrous and Boosted applications are limited to a single throttle body and N/A entries are permitted two.


Aftermarket carburetor is permitted. Spread or Split carburetor is permitted.


Throttle control must be operated by the driver’s foot


VP Racing Fuels Gasoline, Q16, M1, C-85, and E-85 are the only fuels permitted. Diesel combinations must use VP Racing Fuels Torque Diesel (Car must be equipped with fuel sample valve). Event Tech Director reserves the right to inspect fuel at any time during competition Failure to pass Fuel Check is grounds for disallowance of the run during competition and disqualification from the event during eliminations. Fuel is checked using various means. Samples given to Fuel Check Technical Inspectors are compared to data taken from known fuel samples provided by VP, adjusted for temperature, and within a tolerance determined by Event Tech Director. Failure occurs when the sample readings fall outside those tolerances.



Clutch and flywheel meeting SFI Spec 1.1 or 1.2 up to a twin-disc maximum is mandatory. Steel flywheel shield meeting SFI Spec 6.1 is mandatory. Flywheel shield cannot be modified for clutch adjustment and/or cooling holes


Aftermarket transmissions with a maximum of 5 forward speeds are permitted. Clutchless transmissions are permitted. All gear changes must be a direct action of the driver. Pneumatic, electric, hydraulic, etc. shifters are prohibited. (Import exempt)


Any OEM or aftermarket automatic transmission is permitted. Lockup convertors permitted. Trans-brakes are permitted. Pneumatic, electric, hydraulic, etc. shifters are permitted. Bruno converter style transmission prohibited. Any entry with lock up will carry the lock up weights regardless of use.


Any steel, aluminum or carbon fiber driveshaft meeting SFI 43.1 spec is required.


Any automotive type rear-end is permitted.



Front and rear hydraulic brakes are required. Automated brakes are prohibited. The application and release of the brakes must be a function of the driver. Dual reservoir master cylinder is required. Line-lock is permitted only on the front wheels using one line-lock button and solenoid. Any other electrical, pneumatic, hydraulic, etc. switch in braking system is prohibited.


Any American production type steering system permitted.


Aftermarket stock-type shocks/struts permitted.


Factory type front suspension only. Coil over shocks are allowed. Aftermarket replacement control arms are allowed. Aftermarket K-Members/Commercially available sub-Frames allowed. (Must have prior approval from tech) Strut towers must be in factory location with factory sheet metal attaching factory frame rail to top of strut tower, can be notched, windowed, or trimmed for header clearance but must maintain factory sheet-metal attachment.

Pre-1978 and Older Vehicles: The use of aftermarket bolt-on front suspension kits for engine fitment is permitted. Factory strut/shock towers are optional in pre-1978 vehicles using an aftermarket bolt-on front suspension kit.


Stock-type, ladder bar, and OEM COPO/Drag Pak/Cobra Jet suspension systems are permitted. NHRA SS GT/Super Mod FWD conversion keeping rear frame rail permitted. 4 link permitted on SB NOS Combo without penalty. *see weight add


The use of wheelie bars is not permitted.



All vehicles must have a chassis that meets the guidelines set by SFI for their respective speed and elapsed time. A valid NHRA serialized sticker is mandatory at an NHRA Member Track.


Stock frame required from the front engine/motor plate to the back of the rear wheel tub. Back-halved cars are prohibited. Front and rear sub frames may be joined together. Horizontal and vertical notching of rear frame rail is permitted for tire/rear end clearance.


All entries must maintain a wheelbase of +/- 1inch from OEM specifications.


A minimum of 3 inches from the front of the vehicle to 12 inches behind front spindle centerline is mandatory. A minimum of 2 inches for the rest of the vehicle is mandatory (except for oil pan and exhaust headers).



All entries have the choice to either use a 28-inch tall by 10.6-inch wide bias slick or a 275/60/15 or Pro Bracket drag radial tire. Tire tread may not extend outside of the fender. Any racing wheel permitted.



Interior must maintain a factory appearance. Any aftermarket racing style seat is permitted. Driver’s seat must be located in the stock location. Passenger seat is not required. Door panels are required. Floor and transmission tunnel where visible must be carpeted or upholstered.



All Vehicles must retain its original appearance, profiles, and dimensions must be used for year being used. OEM body shell must be intact. Light weight body panels are restricted to hood, front fenders, doors, deck-lids/trunk lid, hatch, and bumpers only. All front ends must be of factory dimensions. Any beam tripping devices forward of the bumper are prohibited. Composite roof panels are permitted on 2005 and newer vehicles. One piece frontends will be legal but must have a means of removal for safety in the event of a fire. (Track tech official will have final say) A hood must be used: scoop or hood must cover the entire induction system. Forward facing hood scoops/ turbo or supercharger inlets are permitted. Alterations or aerodynamic modifications are prohibited. Any aftermarket/modified front bumper/valence must have prior approval from the Event Tech Director tech. Pre-64 body will receive a 25 lbs. deduct.


Forward facing hood scoops are permitted for nitrous assisted entries and may not extend above the roof line. Vehicles that are equipped with an EFI system are not required to run a hood scoop. Carburetors must be completely covered by the hood or hood scoop. Sensors, transducers, vents, wiring, hoses/lines, etc. are prohibited from being inside the hood scoop.


All entries are required to have an OEM cowl area, except 4th Gen GM F-body vehicles.


Factory Grille or facsimile (painted or decal) permitted.


Stock, factory firewall location is required. Notching and smoothing of firewall is permitted but must be identifiable as being in the factory location. Factory OEM fiberglass firewalls (Corvette) are permitted to replace the factory firewall with a minimum of .024 thick steel located in the factory location. No part of mid-plate may attach or support the firewall.


Fender splash pans may be altered.


All entries are permitted to use Lexan windows.


All entries are required to have stock floor pans on both the driver’s side and passenger’s side of vehicle. Transmission tunnel may be removable and must be made of either .024 inch thick steel or .032 inch thick aluminum. Removable floor panels are prohibited. Patching permitted.


All entries all permitted to use steel, aluminum, or carbon fiber wheel tubs.


All entries are permitted to use rear wing/spoilers. Wing/spoilers are allowed a maximum length of 26 inches. Any adjustments to the wing/spoiler during a run are prohibited.


All entries must have operational headlights and/or fog lights and taillights.


All cars in competition must be painted or wrapped. Advertising graphics are permitted on the body. In order to be eligible for the X275 points championship program, all sponsors’ decals must be easily visible and located on the outside of the vehicle. Failure to do so can result in the driver forfeiting all claimed championship points for that particular event. The X275 points championship program requires that all entries run the following decals:

1. Championship Windshield Banner: Decal needs to be located on the top of the windshield or just above the windshield located on the body.

2. Championship Series License Plate: Plate must be located on the front of the vehicle

3. Class Sponsor(s): Decal must be located on the passenger’s side lower portion of the windshield.

4. Class & Competition Numbers: Numbers must be easily visible/legible and located on the front, back, and both side windows.



A maximum of two batteries is allowed.


Any battery operated ignition system and distributor drive system is permitted.


All entries must be self-starting with an on-board starter.


An operational master cutoff switch is mandatory.



Computer/data recorders are permitted and must standalone and to be only used for information gathering purposes.


The use of any device (electrical or mechanical) that allows a driver to ascertain the position of their car on the track prohibited.


A maximum of one pressurized container (excluding nitrous and fresh air systems) per vehicle is permitted. All pressurized bottles must meet D.O.T. 1800lb minimum specification.


The use of tow vehicles is permitted.
X275 reserves the right to adjust the rules at ANY TIME.