Motorcycle engines: Understanding your bike's power and performance

A motorcycle engine works just like a car engine, but on a smaller scale. You’ll generally see them classified according to the following characteristics:

• Number of cylinders and their layout—single, parallel-twin, inline-three, inline-four, V-twin, L-twin, V4, and flat-twin

• Capacity and power output of the combustion chambers—measured in ccs, ranging from 50cc to 1000+cc

• Number of strokes in the power cycles—two- or four-stroke

• Engine cooling system—air- or liquid-cooled

Each component of the engine works together to dictate power and performance.

• Cylinder block and cylinders: the main body of the engine and the chambers where combustion takes place

• Piston and piston rings: the pieces that move within the cylinder and the rings that create a seal between the piston and the cylinder

• Valves: spring-loaded flaps that allow the air/fuel mixture to enter and the exhaust gases to exit the cylinder

• Fuel system: delivers fuel and air to the cylinder for combustion

• Spark plug: ignites the fuel and air mixture in the cylinder to create combustion

• Crankshaft: rotating shaft that converts the piston motion into rotational motion to power the back wheel

• Camshaft: a shaft that controls the opening and closing of the intake and exhaust valves

• Cooling system: regulates engine temperature in a liquid-cooled engine by circulating coolant and dissipating heat

• Exhaust system: carries exhaust gases away from the engine and reduces engine noise

Motorcycle engine power is a core selling point and differentiator when you’re comparing different types of motorcycles. If you’re looking for a bike that gets going and reaches top speed quickly, you’ll want more engine power. If you’re new to riding or are looking for a cruiser, you can get by with less engine power.

Engine power is determined by a combination of factors, and you’ll see it measured a couple of different ways. We’ll explore the variables below.

Torque refers to the engine’s twisting force. The pistons and cylinders transmit power to the crankshaft that turns the rear wheel and does the work of propelling the bike forward. More torque means there is more power readily available at any given time. So, for example, you can accelerate faster from a dead stop or pull strongly uphill.

Horsepower (hp) assesses the rate at which the engine performs the work. When the engine is doing the same amount of work, but faster, it’s producing more hp. We measure the rate in the horsepower equation in revolutions per minute (rpm). When the engine spins quickly—a high rpm—it achieves a higher horsepower.

The horsepower calculation isn’t especially useful to the average rider—not to mention that motorcycle manufacturers don’t typically advertise hp in motorcycle sales. But a higher hp generally translates to faster acceleration at speed and a higher overall top speed.

A motorcycle’s cc measures the total volume of the engine’s cylinders, or the amount of space dedicated in the engine to combustion. Large engines—meaning they have a higher cc—generally have the potential to produce more power.

Other factors, including engine design, number of cylinders, valve timing, fuel quality, and exhaust systems can greatly impact how an engine with a specific cc performs.

Combustion involves an engine’s pistons squeezing the air/fuel mixture in the cylinders. More compression makes it burn more powerfully and efficiently once ignited.

The compression ratio compares the volume of the cylinder when the piston is at its lowest point to the volume of the cylinder once the piston reaches its highest point—called the combustion chamber—where the mix is ignited.

At a higher compression ratio, the air/fuel mixture produces more power, which then pushes the piston with more force.

Engine displacement describes how much total air and fuel are moved or "displaced" by the pistons in the engine cylinders on each cycle. Motorcycle engines with larger displacements—which we measure in cc—can process more fuel and air, producing high horsepower and torque. Traditionally, increased displacement enhances engine power, but modern engine technology can often achieve higher hp with a relatively small displacement.

The main job of the exhaust system is to efficiently release used gasses so the engine can take in fresh air and fuel. When this process runs smoothly, the engine fully uses each injection of the air/fuel mixture. This can mean better fuel efficiency, the bike running smoother, and more power.

Motorcycle engine tuning involves adjusting the fuel-air mixture, ignition timing, and exhaust system to optimize performance. Some tuning can be done through the engine’s computer—electronic control unit (ECU)—while some is done manually.

Tuning can enhance your bike’s power output, fuel efficiency, and overall engine performance. It can ensure that your motorcycle runs smoothly and efficiently, providing you with the best riding experience possible.

If you want to increase horsepower or overall engine performance, consider the following upgrades and modifications:

• Increase your bike's air intake: This is an easy and economical modification. However, increasing your airflow can also mean more fuel consumption. So, you may also need to tune your fuel injection or carburetor to ensure the right air mixture ratio.

• Install a new exhaust system: Expel exhaust gases more efficiently and let your engine breathe better with a new exhaust system. You may also notice your bike sounds better.

• Perform an engine control unit (ECU) tune: This is another common mod. The type of system you go with will depend on your bike. For example, Honda's ECUs are relatively simple, so a reflash will work, whereas other bikes benefit from a piggyback system to edit engine mapping more effectively.

If you’re having issues with your engine’s performance, it’s helpful to be able to recognize and diagnose some of the most common offenders.

• Loss of power: For your engine to run properly, it needs air, fuel, and spark. If any of these aren’t supplied to the combustion chamber in the right amounts at the right time, your engine most likely won't run smoothly and could lose power. Common causes include a faulty spark plug, clogged air filter, improper oil levels, or bad gas.

• Overheating: There are multiple reasons why motorcycle engines overheat, including low coolant levels, a cooling system leak, a faulty thermostat, a blocked radiator grille, a malfunctioning water pump, and an overloaded engine. If this happens, stop riding, let the engine cool down, try to diagnose the issue, and seek professional assistance.

• Engine knocking or pinging: Improper detonation is usually the cause of engine knocking. If you hear engine knocking, discuss this issue with your mechanic. You may be able to eliminate it by increasing the fuel's octane number.

• Poor fuel efficiency: If you're not getting the mileage you'd expect, your engine might run rich, which points to your fuel delivery system. The system may be delivering too much gas and not enough air. Signs of this include sputtering, running poorly, and backfiring.

Keep your motorcycle running smoothly and safely with these simple engine maintenance tips:

• A clean oil circuit and regular oil changes are necessary for proper performance. Change your oil based on the mileage intervals suggested in your bike's service manual (typically every 3,000 to 5,000 miles).

• Check your air filter every few months and replace at least once annually, depending on how much you ride.

• Check and adjust valve clearances—you can do this yourself with the right tools.

• Regularly inspect coolant levels and quality. You should complete a full flush at least once every two years.

• Conduct routine inspections to look for leaks, which could indicate issues with seals or gaskets.

Tip: For detailed seasonal motorcycle maintenance, refer to this checklist.