Terms to Know
You’ll find these Nitro R/C engine terms throughout this section of the manual.
.15
- .15 or “15” refers to the displacement of the engine. The TRX 2.5R
Racing Engine is .15 cubic inches or 2.5 cubic centimeters (cc). The name
“TRX 2.5R” is derived from the cc measurement.
ABC
- Abbreviation for aluminum, brass, and chrome. Refers to engine
construction that consists of an aluminum piston that slides in a chrome-
plated brass sleeve. The TRX 2.5R Racing Engine uses ABC construction.
Air filter
- The air filter sits atop the carburetor and prevents harmful dust
and dirt from entering the engine. Dirt ingestion is the number one cause
of premature engine failure so the engine should never be run without the
air filter in place.
Big Block .15
- A .15 (2.5) engine that uses a larger crankcase size and longer
stroke than typical .15 engines. Generally only used for specific racing
classes.
Break-in
- Break-in is the procedure for running a brand new engine
according to specific instructions. This correctly prepares the engine for
normal running. The break-in procedure can be different for different
makes of engines. Follow the Traxxas directions for break-in exactly.
Carb
- Abbreviation for carburetor.
Carburetor
- The carburetor atomizes (mixes) the fuel with the air so that
the engine can burn it. There are two types of carburetors, slide carbs and
barrel carbs. The TRX 2.5R uses the superior slide carburetor design.
Clean-out
- Cleaning-out is a condition that occurs when the engine is
accelerating and the fuel mixture becomes sufficiently lean to allow the
engine to continue into its upper RPM power band. Usually characterized
by a noticeable decrease in blue exhaust smoke and a dramatic increase in
engine speed.
Combustion chamber
- The combustion chamber is machined into the
bottom of the cylinder head. This is where the glow plug ignites the fuel.
The shape of the combustion chamber is designed to promote more
efficient burning of the fuel.
Connecting rod
- The connecting rod transfers the piston motion to the
crankshaft. The TRX 2.5R Racing Engine uses a “knife-edged” connecting
rod. The aerodynamic, sharpened edges allow it to “slice” through the
pressurized air/fuel mixture inside the crankcase.
Cooling fins
- The cooling fins are molded into the cylinder head and
crankcase and cause heat to be drawn away from the engine. Heat is
removed when it dissipates into the air passing across the cooling fins.
It is important to keep the fins clean of dirt and debris for maximum
cooling efficiency.
Crankcase
- The engine “body” that contains all of the running
mechanical components.
Crankshaft
- The main shaft of the engine that contains the
rotating assembly.
Cylinder head (head)
- The finned aluminum part on top of the engine that
is responsible for dissipating most of the engine’s heat. The combustion
chamber is machined into the bottom of the head.
Damper
- Another term for shock.
Damping
- Resistance force caused by the piston moving through the oil
used to absorb bump and spring rebound energy.
Dyno
- Abbreviation for dynamometer. A precise piece of testing equipment
that accurately measures engine power and torque output over the
engines entire RPM range.
EZ-Start
- Second generation Traxxas on-board electric starting system. The
system consists of a hand held starter control unit and an on-board
gearbox with an electric motor to spin the engine.
Filter foam
- The oiled foam element inside the air filter housing. The filter
foam in the TRX 2.5R Racing Engine must be thoroughly cleaned and re-
oiled after every hour of run time.
Fit
- Usually refers to the fit of the piston and sleeve. If the fit is tight, then
the piston will feel very tight at top of the sleeve and the engine will have
good sealing and compression. If the fit is loose, then compression will be
low and the piston and sleeve should be replaced.
Flame-out
- Occurs when the engine stops running at high RPM. Usually the
fault of an excessively lean fuel mixture or glow plug failure.
Fuel
- (10% 20%) The TRX 2.5R must have model engine fuel to run. Traxxas
Top Fuel is recommended. Fuel is sold in quarts and gallons from hobby
dealers. The 10 and 20% labeling refers to the percentage amount of
nitromethane contained in the fuel (see “nitro percentage” definition).
Fuel mixture
- The ratio of fuel to air as determined by the needle settings
of the carburetor.
Fuel tubing (fuel line)
- The thick silicone tubing that carries fuel from the
fuel tank to the carburetor.
Glow plug
- The glow plug is located in the cylinder head at the top of the
combustion chamber. It contains a platinum element that glows red hot
20 • Revo
The TRX 2.5R Racing Engine
