Nitro Engines for Your Nitro RC Cars

Nitro Engines: 2-Stroke

The 2-stroke is the engine most commonly found in nitro RC cars and trucks. “Stroke” is meant by the number of times the piston travels through the engine sleeve in the combustion chamber.  2-stroke engines produce power in one cycle, which is divided into the two “strokes.”  The piston has two positions: top dead center where the cycle begins and ends, and bottom dead center, which is the middle point of the power cycle.  Combustion causes increased pressure in the chamber and forces the piston down.  As this occurs, the exhaust ports are opened so gases can escape through the manifold.  The second stroke begins when the piston reaches bottom dead center and the crankcase and then moves back up the engine sleeve.  This causes the pressure to build up again as the piston approaches TDC once again, completing the power cycle.  The next stroke occurs as soon as combustion from the glow plug sparks it again.

Nitro Engines: 4-Stroke

Less common but more powerful, 4-stroke engines are more like what you’ll find under the hood of your real car or your lawn mower.  Though similar to a 2-stroke, a 4-stroke engine has 2 full cycles with 2 strokes of the piston each (for a total of 4 strokes).  Unlike the simpler glow-plug ignition that a 2-stroke uses, a 4-stroke regulates the air and fuel in the chamber with a geared cam mechanism. Intake timing is how much and when this air/fuel mixture enters the cylinder, while exhaust timing refers to the escape of hot gas from the cylinder. 

The easiest way to understand what happens in the 4-stroke power cycle is imagine the 2-stroke cycle simply stretched out to get the most out of each segment of the piston’s movement.  The piston begins at TDC and as it travels down the cylinder the geared cam allows fuel and air into the combustion chamber. 

The intake valve closes when the piston reaches the bottom of the cylinder, which is then forced back up by the flywheel and drive train components.  This compresses the air and fuel, and the pressure causes combustion as the piston reaches the top of the cylinder again, completing what is referred to as the compression stroke. 

As the fuel mixture ignites it initiate the so-called combustion-stroke, during which the piston travels back down the cylinder and up again.  In the final “power” stroke the gases are forced out to the exhaust systems—just as in the 2-stroke engine.  The cycle is then repeated.

All 4-stroke engines rely on intake and exhaust valves to complete their power cycle.  This is combined with a number of other features—a moving crankshaft, several valve-train components, camshaft, rod and pistons and the geared cam mechanism—to make a more powerful, but more advanced engine.  The improved management of fuel and air flow in and out of the engine makes the 4-stroke more efficient, though their advanced mechanisms mean they require meticulous attention and maintenance.