Here is the NEW ROAR rules where .15 nitro engine are legal as long as there are not the Big Block type like the Traxxas 2.5. Leave you options open as there will be .15 you can race
ROAR 2003 Nitro rules:
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NITRO FUEL RULES
6-1: The minimum acceptable outer barrier for 1/10 off-road is 1/2” x 4” plywood. For 1/10 onroad
and 1/8 off and on-road, the minimum is 3/4” x 8” plywood. The minimum for any scale oval
track is 3/4” x 11 7/8” plywood (see Rule 1-27 for additional information). The ends of the barrier
must be linked so that no sharp edges or overlaps face the direction of travel.
6-2: Interior lane markers should be 2” x 4” boards, or similar material, on edge, and should be
anchored to the race surface. On off-road courses, 3” smooth PVC pipe is acceptable.
6-3: Fuels will contain only methanol, nitromethane, and a lubricant. The following additives are
specifically prohibited: hydrazine, hydrogen peroxide, propolene oxide, and toluene. Old fuel, not
stored in the original container, can become unstable and should not be used
6-4: Fuel tanks must be securely mounted. Maximum fuel system capacities are 75cc for .12,
80cc for .15 engines, and 125cc for .21 engines. For measurement purposes, 1cc is equal to 1ml.
6-5: Any carburetor may be used as long as the bore does not exceed the maximum allowable for
the engine size. Restrictors may be used to achieve the legal diameter, but must be securely
fastened in place.
6-6: There are two approved ways to determine the fuel capacity of a vehicle. The first way is by
pouring the correct amount into the vehicle's system, and the second way pumps the fuel out of
the vehicle's system into a measurement container. The Race Director must insure that all waste
fuel is disposed of properly. To check a tank capacity the first way, drain all fuel from the system
including fuel and pressure lines. Pinch off the pressure line at the tank, and disconnect the fuel
line from the carburetor. Using a graduated cylinder, measure the proper amount of the driver’s
fuel and pour it into the tank, allowing fuel line and filter to fill. The fuel should fill the tank to the
top of the filler neck, or to a point where fuel overflows or is forced out when the lid is closed. If it
does not, the tank is oversize and must have an insert added to bring it down to legal capacity.
The graduated cylinder is read at the bottom of the center of the curve when viewed from the side
of the cylinder at eye level.
To check the tank capacity the second way, fill the tank to the top of the filler neck. Make sure
all fuel lines are full. Attach a fuel pump or large capacity syringe to the end of the tank-to-engine
fuel line. Transfer the fuel completely out of the vehicle's system into a graduated cylinder or
another accurate liquid measuring device. (Reading a graduated cylinder is described above, in
this rule.) If there is more fuel retrieved than allowed, the tank is too big and an insert must be
used to reduce the tank capacity.
6-7: Any type of bearings and any connecting rods may be used,(except ceramics).
6-8: Engines must be of single cylinder, two stroke, air cooled, glow plug design. Only one single
throat carburetor is permitted. No supercharging or turbocharging is allowed. Only standard glow
plugs with 1/4-32 thread, using a .25” gasket, will be allowed in .12 and .15 engines. Turbo style
plugs are permitted only in .15 Open and .21 Open engines.
6-9: Cars must have brakes in working condition capable of stopping and holding them
motionless with the engine running. Cars must also have an operational de-clutching device.
6-10: Increasing the displacement of a .12 engine to .15 by changing or modifying the piston,
sleeve, and head is illegal unless the new displacement is permanently indicated on the head.
6-11: Exhaust port height is the distance from the top of the piston, at bottom dead center, to the
highest point of the exhaust port on the piston side of the sleeve. Shims may be used to adjust
exhaust port height.
6-12: To determine the displacement of an engine measure the diameter of the bore, divide this
number by 2, square the number, and multiply the result by Pi (3.1416). This result is then
multiplied by the stroke. To calculate the stroke measure the distance from the top of the sleeve
to the top of the piston at its bottom most position in the engine (bottom dead center) and subtract
the distance from the top of the sleeve to the top of the piston at its upper most position (top dead
center). As an example, if the bore measures .55” and the calculated stroke is .543” Then: .55/2 =
.275, .275 x .275 = .075625, .07625 x 3.1416 = .2376, .2376 x .543 = .1290cu.in. .1290 is the
maximum legal size of a .12 engine. An engine with the same stroke but measuring .595” in bore
would yield a displacement of .151cu.in., legal for a .15 engine but not legal as a .12.
6-13: All cars are required to use a muffler or tuned pipe through which the exhaust gas must
pass. Exhaust discharge must be parallel to the ground or lower. The maximum allowable sound
level is 85 decibels, measured at a ninety degree angle to the side of the car from a distance of 33
feet, 3 feet above the ground, with the car at maximum throttle and at all speeds. A Radio Shack
sound meter (Part #33-2055) or equivalent should be used to check the sound level.
6-14: Muffler outlet pipe must be a round, constant diameter tube, with the end cut at 90 degrees
to its centerline.
6-15: An industrial quality dial or digital caliper or go/no-go gauges should be used to check
engine specifications.
6-16: A car that loses its muffler will be black-flagged and not scored until repairs are made.
6-17: Variable exhaust timing, porting, or exhaust pipes with moveable parts are not allowed.
6-18: All gearboxes must be on a single shaft. Multiple-speed transmissions are allowed for
some on-road classes (see vehicle specifications), but not for off-road racing. Automatic or
variable overdrive systems are not allowed.
6-19: Hydraulic drive systems are not allowed.
6-20: Antennas must be the flexible type. Roll-over antennas are not permitted in any class.
6-21: In case of servo or linkage failure, cars must incorporate a positive action return spring
attached directly to the carburetor throttle arm to provide positive closure. Use of "fail safe" radio
systems is highly recommended.
6-22: A pit lane that has a convenient and safe exit from, and entrance back to the racing surface
will be provided. This area is to be used for refueling and repair of cars. There must be a safety
wall between the pit lane and the working pits. All refueling and repairs to the cars will be
accomplished in the working pits, and not in the pit lane. During qualifying, one pit member per
car will be allowed in the working pits. During the mains, two are allowed.
6-23: Engines, fuel tank capacities, carburetors, and other specifications may be checked at any
time by any event official.
6-24: Open flame or smoking is prohibited within 50 feet of areas where fuel is present.
:. Will one of these engines drop right in to my xxx-nt?
