What's the Difference Between 2-Stroke & 4-Stroke Engines?
As you may know, 2-stroke and 4-stroke engines are two types of internal combustion engines commonly used in all-terrain vehicles (ATVs).
Two-stroke engines are coming back thanks to a more usable power band and new engine designs that reduce emissions, are easier to start in cold temperatures, and are ideal for use in snowmobiles.
However, 4-stroke engines produce more torque at lower rpm, generally have better durability than high-revving two-stroke engines and provide improved fuel efficiency and lower emissions.
So, which is right for your quad?
To understand the difference between a 2-stroke and 4-stroke engine and how these differences can be useful to determining which will be useful for the performance out of your ATV, let's look at:
- How they each function to power ATVs
- How main characteristics compare
- Advantages and disadvantages of each engine type
How do They Function?
Before listing the characteristics and applications of 2- and 4-stroke engines, let’s get a few basics straight.
First, the terms two-cycle and 2 stroke are often interchanged, as are 4-cycle and 4 stroke. Each upward or downward movement of pistons in the engine is called a stroke.
Second, they work by converting chemical energy into mechanical energy used to power a quad via a combustion event requiring air, fuel, and a source of ignition.
Therefore, the fundamental difference between two-stroke and four-stroke engines is how they introduce air and fuel for combustion to create power and remove exhaust gases after each combustion cycle.
Generally, a 2-stroke engine uses ports on either side of the piston to control the gases that enter and exit the cylinder. A moving piston covers and uncovers the ports to open and close ports like a four-stroke engine. A 4-stroke engine uses valves to cover and uncover the ports.
The combustion process in a 4-stroke engine:
- Intake and exhaust ports are positioned at the top of the combustion chamber.
- Intake and exhaust valves close as the piston compresses the air-fuel mixture in preparation for combustion.
- During the power stroke, both the intake and exhaust valves are closed as the spark plug ignites the mixture of air and fuel, forcing the piston down and turning the crankshaft.
- As the piston travels up, it forces any gases remaining from the combustion cycle out through the open exhaust valve, preparing the cylinder for a fresh charge of air and fuel.
The combustion process in a 2-stroke engine:
- The intake port opens as the piston moves up, which creates a vacuum as the piston that forces air to rush into the crankcase.
- As the air travels through the carburetor, it picks up a dose of fuel and oil. The piston continues up, compressing the air-fuel mixture in the cylinder.
- As the piston reaches top-dead-center (TDC), the spark plug ignites, causing the air-fuel mixture to explode.
- The piston is forced down by the explosion and the pressurized oil-fuel mixture in the crankcase is forced through the transfer port into the cylinder. The incoming charge forces remaining gases in the cylinder to be released through the exhaust port.
How do They Compare?
The Yamaha Banshee is famous for being a 2-stroke ATV, so riders may wonder how it compares to 4-stroke quads. The Banshee offers a unique blend of high-power output and lightweight construction, making it particularly well-suited for dune jumping or racing, where a high power-to-weight ratio is desirable.
Let’s take a look at other characteristics of the popular 2-stroke and compare them with 4-stroke designs.
- Power delivery: A 2-stroke engine completes a power cycle (intake, compression, power, exhaust) in just two strokes of the piston (one upstroke and one downstroke), while a 4-stroke engine completes a power cycle in four strokes of the piston (two upstrokes and two downstrokes).
- Complexity: The Banshee's 2-stroke engine is simpler in design compared to a 4-stroke engine, which is more complex due to the additional valvetrain components and camshaft.
- Cost: Because 2 strokes are simpler, it’s much cheaper to rebuild or boost the horsepower. They respond better than 4 strokes to bolt-on modifications, making any engine work a fraction of the cost.
- Lubrication: A 2-stroke engine typically achieves lubrication by mixing oil with the fuel, resulting in constant lubrication of engine components, while 4-stroke engines are lubricated through a separate oil system, with oil stored in a sump and circulated via an oil pump.
- Power output: A 2-stroke engine produces more power per unit of engine displacement due to its simpler design and faster cycle, while a 4-stroke tends to have smoother power delivery and better low-end torque.
- Fuel efficiency and emissions: A 2-Stroke engine is less fuel-efficient compared to a 4-stroke engine due to the loss of some unburned fuel/oil mixture during the exhaust stroke, which also creates more emissions. A 4-stroke has a better combustion process and lower fuel wastage and fewer emissions.
- Maintenance: The 2-stroke Banshee requires more frequent maintenance due to its simpler design and higher operating speeds, while a 4-stroke requires less frequent maintenance intervals.
Common Applications for 2- and 4-Stroke Designs
As mentioned above, when we compared the characteristics of 2- and 4-stroke engines, the 2-stroke has the advantage when it comes to power-to-weight ratio, agility, and simplicity, while a 4-stroke design will initially cost more but need less maintenance, have higher fuel efficiency, less emissions, and better reliability.
So, which design is best for what you need?
Well, if you plan to take your quad out recreationally, you have your choice.
Four-stroke ATVs are popular choices for recreational riders who enjoy exploring trails, dunes, and other off-road terrain. Their smooth power delivery and comfortable ride make them ideal for leisurely rides with friends and family.
However, many prefer 2-stroke ATVs for recreational riding due to their lively performance and exhilarating power delivery. Riders who enjoy aggressive trail riding, dune jumping, or freestyle riding often choose 2-strokes for the adrenaline rush.
Here are some other common applications for both.
Four-Stroke ATV Applications:
- Utility work
- Hunting and Fishing
- Agricultural use
- Search and Rescue
- Extended trips and exploration
- Competitive racing
Two-Stroke ATV Applications:
- Motorsports racing
- Extreme terrain
- Freestyle and stunt riding
- Technical trails
- Entry-level riding
Overall, 2-stroke ATVs are valued for their agility, lower cost, lightweight design, and spirited performance, while 4-stroke ATVs cater to extended recreational and commercial riding, as well as industrial use.
POWER UP
Since 1998, Vito’s Performance has been supplying the world with top-quality and hard-to-find ATV parts for builders and enthusiasts alike. We specialize in the Yamaha Banshee and the Yamaha Blaster, and carry parts for all Yamaha Raptors, the Yamaha Warrior, Honda 300ex and 400ex, and the Honda TRX450r. For assistance with all performance products, contact Vito’s Performance online or call (248) 969-9168.