Light Modified Rules
Updated: Jan 19
Maximum weight 6000# unless noted otherwise
Hitch Height 20”
Weight is 6000lbs no tolerance unless noted
Allowable fuels, alcohol, diesel, kerosene, any form of gas/race gas, absolutely no nitromethane or nitrous oxide allowed.
EFI is allowed on any engine combination listed below.
Maximum of one 600ci hemi headed v8 automotive style engine with a maximum blower size of 14-71, no screw blowers or turbos allowed. Variable speed supercharger devices prohibited.
One fuel injected Allison v12 aircraft engine limited to 8.8-1 supercharger overdrive ratio.
Allow Allison (alcohol ok) to run one turbo per bank as a trial (cast wheels in turbo, no billet wheels), with no intercooler or supercharger.
One carbureted gas Allison v12 aircraft engine limited to 9.6-1 supercharger overdrive ratio.
One carbureted gas Merlin or Packard style v12.
Any combination of N/A wedge head automotive style engines with a combined displacement of 1500ci (no power adders).
Under 710ci N/A will be allowed to run at 7000lbs.
Any combination of forced induction wedge head automotive style engine with combined displacement of 750ci air forced induction. 2 big blocks (650ci ea max) with max 8-71 Blowers can run with Percentage of OD reduced on blowers, Hi Helix reduced more… (Approx Hp each 1250HP)
A) Turbos limited to one per bank 76mm inducer compressor side, 76mm exducer turbine side for aluminum headed engines and 88mm inducer compressor side, 88mm exducer turbine side for cast iron heads.
B) Under 355ci will be allowed to run at 7000lbs.
C) Any type of engine driven blower excluding screw type no over drive limit no variable speed device. D) No intercoolers allowed.
E) Cannot run blower(s) combined with turbo charger(s).
F) If more than one power unit under 750 ci, if turbochargers are used, will be limited to max of (2) 88mm turbos per vehicle.
10) Any agricultural engine with a cubic inch of 505 or less on alcohol, or any cubic
inch diesel (2 stages turbo max) may be used.
Aftermarket aluminum heads allowed no overhead cams or hemi style combustion
B) Alcohol 510 to 640 cubic inch motors are limited to one (1) 4.1 max. turbocharger.
Twin Lycoming L-1, L-11 allowed military specifications. One Avco Lycoming T53 turbine or one GE T58 turbine. Twin Turbine combo, L-11, T-53 rated at 2200 hp or less is allowed.
A) No turbine engine will be operated beyond military temperature and RPM limits.
B) Turbine engine or combinations of turbine engines are allowed maximum military rating of 2500 HP. Any engine or combination of turbine engines with HP rating of 2200 or less are allowed water/methanol injection. Nothing allowed to be sprayed or injected in the airstream of the intake or turbine engines that total more than 2200 horsepower. All turbines to have over-speed safety devices set to a maximum of 100%.
C) T53 will be allowed to weigh 6200#
D) Any combination of automotive style diesel engines limited to 900ci displacement may run one turbo per engine limited to 3” inducer compressor side and 3.5”exducer turbine side. No intercoolers, Water injection is allowed.
E) Under 450ci will be allowed to run at 7000lbs
F) One 1100ci Ford GAA engine on alcohol limited to two non-staged turbo chargers. 88mm is allowed
12. Griffon Rolls Royce will run on low supercharger speed, and with an intake restrictor to 5”.
Any motor combination not already mentioned in the rule book must be approved by the RRTTPA Board.
All superchargers must be mounted to the intake by use of aluminum studs. STEEL STUDS PROHIBITED!
Supercharger restraint system is mandatory and shall consist of four separate straps, one on each corner of the supercharger and sandwiched between the charger and injector. Safety straps must be connected to the exhaust flange on the cylinder head.
Supercharger belt shield must be wider than all components, idler, belt, pulleys, etc. and extend to the bottom of the crankshaft.
No screw type superchargers allowed.
Turbo chargers are allowed to be ran on V8 engines (1) 88mm turbo with a billet wheel or (1) holset turbo up to 4 inches with cast wheel in and out non-staged turbo per bank on (1) V8 automotive engine with a maximum of 600 cubic inches. Iron cast heads only.
No turbine engine will be operated beyond military temperature and RPM limits.
Turbine air intake must be screened with metal screen that has openings no larger than 3/16-inch.
Turbine engines must have a 3/8 steel shroud that surrounds the engine. Shroud must extend a minimum of 5 inches forward and ten (10) inches to the rear of
the turbine section. The shroud must incorporate a minimum of 3/8-1/2” thick
flanges (under 1500 hp will have a 3/8”, over 1500HP will have a ½” steel shielding) that extend radially inward from the shroud on both ends of the
shroud with a maximum of 1 inch of the engine casing. A ½ inch gap between
the engine and the ID of the flange must be maintained for air circulation inside the shroud. The flanges may be scalloped out to clear turbines accessories, brackets, etc. And maybe either rolled edged of the shroud or steel rigs attached by welding or riveted to the shroud.
Two independent over speed protection devices are required to power turbine wheel.
The governor setting must not exceed manufacturer’s maximum specs. Over speed shut down consist of speed monitor that activates a normally closed solenoid valve located between the fuel control and fuel manifold. Trip setting to be low enough to prevent over speed in event of driveline failure. No TF-35 or T55-L-11 engine allowed.
Turbine engines allowed starter motor onboard or auxiliary power unit to be carried onboard and running during a competitive attempt but must not be hooked into the drive train during competition attempt
No turbine engine is allowed to run a clutch/flywheel assembly or any automatic transmission.
Exhaust pipes on turbines must extend a minimum of 6 inches above the top of the exhaust opening.
Exhaust stack diameter to be no smaller than 1 inch of engine outlet.
Naturally aspirated aviation engines, the gearbox output shaft must not exceed one and one-half the speed of the crankshaft.
Mechanical clutch equipped vehicles must have a SFI approved explosion-proof bell housing and a “block saver” steel or aluminum plate between the engine and bell housing. Bell housing must be bolted to a ¼ or greater steel plate with a minimum of (12) 3/8-inch bolts (grade#5) evenly spaced around the bell housing,
OR the entire clutch area enclosed front and rear, 360 degree coverage, with min 3/8”steel, ½” away from rotating mass and shall be covered with a 4.2 SFI blanket (min 12” wide) around clutch housing with 6” overlap.
The plate must be securely fastened to the frame by (8) 3/8-inch bolts (grade#5) with (4) bolts on each side of the frame.