16 • T-MAXX
THE TRX 2.5 RACING ENGINE
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 2.5
Racing Engine is .15 cubic inches or 2.5 cubic centimeters (cc). The
name “TRX 2.5” 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 2.5 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.
BDC
- Bottom dead center. The bottom-most position of the engine
piston stroke.
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 2.5 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. It is 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 2.5 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.
Crankcase
- The engine’s “body” that contains all of the running
mechanical components.
Crankshaft
- The main shaft of the engine that holds the
reciprocating assembly.
Cooling fins
- The cooling fins are milled 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.
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.
Dyno
- Abbreviation for dynamometer. A precise piece of testing
equipment that accurately measures engine power and torque
output over the engine’s entire RPM range.
EZ-Start
- 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 2.5 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,
the piston will feel very tight at the top of the sleeve (top dead
center), and the engine will have good sealing and compression.
If the fit is loose, compression will be low and both 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%, 33%) The TRX 2.5 must have model engine fuel to
run. Traxxas Top Fuel
™
is recommended. Fuel is sold in quarts and
gallons from hobby dealers. The 10, 20, and 33% labeling refers to the
percentage of nitromethane contained in the fuel.
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 an element that glows red
hot when voltage is applied. When the engine is being started,
the heat from the glow plug ignites the fuel mixture and starts the
combustion process.
Glow plug driver
- This tool clips onto the glow plug and supplies the
required voltage to light the glow plug element. It is also called an
igniter. EZ-Start equipped engines do not require this separate tool.
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