T-MAXX • 17
THE TRX 2.5 RACING ENGINE
Header
- The aluminum tube that connects the exhaust system to the
engine exhaust port. The length and diameter of the header must be
carefully selected to extract the most power from the engine.
High-speed needle (HSN)
- Adjusts the carburetors fuel/air mixture at
high throttle openings.
Idle speed
- The speed (RPM) the engine runs at when the transmitter’s
throttle trigger is at neutral.
Idle speed screw (ISS)
- Located on the carburetor body. This screw
adjusts the idle RPM of the engine.
Lean
- A running condition where the engine is not getting enough
fuel (for the available air). Symptoms include engine overheating,
or the engine runs for a short time and then stalls, particularly at
high speed. This is a dangerous condition that should be corrected
immediately or it can ruin your engine.
Leaning the mixture
- Turning either the high-speed and/or low-
speed needle(s) clockwise to decrease the amount of fuel the engine
receives.
Low-speed needle (LSN)
- Needle valve that controls the fuel mixture
at low throttle openings.
Needle valve
- Valve consisting of a tapered needle that closes against
a corresponding seat to regulate fuel flow.
Nitro
- Abbreviation for nitromethane, a component of model engine
fuel that improves fuel combustion and power output. Nitro also
refers to a class of R/C powered by model engines instead of electric.
Nitro content
- The amount of nitromethane used in the fuel. Usually
measured as a percentage of the total fuel volume. Traxxas engines
are optimized to use 10-20% nitro. 33% nitro may be used for racing.
Nitromethane
- Nitromethane is a component in the fuel that increases
power from the combustion process up to a point. Engines are
generally optimized to use a range of nitro content for the best
power.
O-ring
- Rubber “O”-shaped ring used as a sealing gasket.
Pipe
- Abbreviation for the tuned exhaust pipe on a nitro engine. See
“Tuned Pipe”.
Piston
- The piston is the internal engine part that is attached to
the upper end of the connecting rod and moves up and down
in the cylinder sleeve. The precise fit between the piston and the
sleeve creates a seal that allows the engine to have the required
compression for combustion.
Port
- Ports are openings in the sleeve that allow atomized fuel to enter
the combustion chamber and burned exhaust gases to exit. The
shape and location of the ports are a large factor in controlling the
engine timing and power output.
Priming
- Manually causing fuel to move from the fuel tank up to the
carburetor. This is sometimes necessary after the engine has been
sitting for a long period of time and all of the fuel has drained back to
the tank. On a Traxxas model, this is done by holding your finger over
the exhaust tip for one or two seconds while the engine is starting.
Punch
- A term that refers to how quickly the model responds to
throttle input or how quickly it accelerates.
Rich
- A running condition where the engine is getting too much
fuel for the available air. It is better to run an engine slightly rich
to increase engine life. Excessively rich mixtures cause the engine
to have sluggish performance with exaggerated blue smoke and
unburned fuel coming from the exhaust.
RPM
- Abbreviation for revolutions per minute (how many times the
engine crankshaft spins in a minute).
Sleeve
- Internal engine part that contains the piston. The precise fit
between the sleeve and the piston creates a seal that allows the
engine to have the required compression for combustion. The sleeve
in a TRX engine is made of brass and is then hard-chrome plated.
Slide carburetor
- The throttle on a slide carburetor closes and opens
by sliding a barrel in and out of the carburetor body. This type of
carburetor is preferred for performance use because it provides a less
restrictive “straight-through” air path than the barrel carburetor design.
Stall
- When the engine stops running, usually due to an incorrect fuel
mixture setting or running out of fuel.
TDC
- Top dead center. The top-most position of the engine
piston stroke.
Tuned pipe
- The tuned exhaust pipe usually consists of a specially-
shaped metal or composite chamber with baffles that is designed to
enhance the power output of the engine.
Wear-in
- Fitment process that occurs during engine break-in where
internal engine parts develop an even more precise matched fit
through actual use under controlled circumstances.
WOT
- Abbreviation for wide-open throttle.
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