Choosing Between 2-Stroke & 4-Stroke Outboard Motors

As time goes by and technologies advance, the differences between 2-stroke outboards and 4-stroke outboards become less pronounced.

When it comes to choosing any type of product over another, it’s always prudent to do your research and come to your own conclusions. So with that in mind, here’s a quick guide to the differences between 2-stroke outboards and 4-stroke outboards to help you decide for yourself which suits you better. 

2-Stroke vs 4-Stroke Outboards - The Differences

Both 2-stroke and 4-stroke outboards generate power by burning a mixture of fuel and air. However, they work in slightly different ways and both have their pros and cons.

2-stroke outboard engine

• Simpler design
• Produces power with every two strokes of the piston within the cylinder
• Doesn’t use valves or camshafts
• Lubricated by oil mixed with the fuel entering through the carburetor or fuel injectors

4-stroke outboard engine

• More complex design
• Produces power with every four strokes of the piston within the cylinder
• Uses valves and camshafts
• Lubricated by oil permanently housed within the crankcase

Emissions

Stricter emissions laws at the start of the millennium severely hamstrung 2-stroke outboards, and marked the point that 4-strokes became more popular.

Older 2-stroke engines were notorious for belching out clouds of hydrocarbons and unburned oil. However, direct fuel injection and other technological advances found in modern 2-stroke engines have brought their emissions in line or close to those of 4-stroke motors. Two-stroke outboards of the distant past may not comply with current or future emissions rules. However, if you’re buying a new outboard, both 2-stroke and 4-stroke motors will comply with current regulations.

Power

In the past, 2-stroke outboard motors were more powerful than 4-stroke outboards of the same size. 

However, the evolution of engine management systems and electronic fuel injection, coupled with lighter, stronger metals and alloys means the gap for performance between a 4-stroke outboard and a 2-stroke outboard has narrowed.

The way a 2-stroke engine generates power means it should provide better hole-shot, which is great for watersports or anything else that requires rapid acceleration. However, a 4-stroke engine generates more torque, so it provides more pull. As boats get larger and better equipped, they also get heavier, so a torquey 4-stroke might be a more suitable option. The smooth powerband of a 4-stroke is also better for cruising long distances at speed.

Size and Weight

Despite the burden of a valve train, refinements in design and materials means the size and weight difference between a 4-stroke motor and valve-free 2-stroke engine is significantly less.

On mid-size and larger outboards (25HP and up), it’s unlikely there’ll be much difference in performance between a 2-stroke and a 4-stroke. On smaller outboards (25HP and below), there might still be advantages to a more compact 2-stroke design. However, the newer the outboard, the less the differences in size and weight will be.

User-Friendliness

Two-stroke engines are generally noisier than 4-strokes, but manufacturers have managed to bring down the noise levels in recent years. Nevertheless, 2-stroke engines still make a higher-pitched sound, which can be more irritating than the quieter 4-stroke.

Two-strokes are known for being “peaky” engines that run better at higher RPMs. This has made them notorious for misfiring at lower RPM and stalling when idling, which isn’t ideal when running in a no-wake zone or maneuvering within a marina. Four-stroke outboards have wider powerbands and run comfortably at any RPM, although electronic engine management and direct fuel injection has made modern 2-stroke motors much more user-friendly. 

Running Costs

Boat fuel isn’t cheap, and outboards can be thirsty beasts. The cost of fueling an outboard throughout boating season can amount to thousands of dollars. 

Four-stroke outboards generally have better fuel economy than 2-strokes. But again, modern technologies have closed the gap significantly. However, 2-stroke motors will always be less fuel efficient by design.

A typical 4-stroke motor needs one or two oil changes per boating season. By contrast, the oil in a 2-stroke motor must be changed all the time, which can become more expensive to maintain. 

Maintenance and Durability

All outboards need regular maintenance regardless of whether they’re a 2-stroke or a 4-stroke unit. 

Check prices for outboards you’re considering buying to see if a particular model or brand will be cheaper to maintain. If you’re not going to be doing the maintenance work yourself, check how much the local dealership for that particular outboard brand charges.

Four-stroke outboards have the edge in reliability because their lubrication systems keep the engine’s moving parts constantly bathed in oil, which reduces wear and increases durability. However, modern technology enables manufacturers to make all their outboards as durable and reliable as possible.

The size, weight, emissions, fuel economy and performance of modern 2-stroke and 4-stroke outboards will be very similar. If you’re looking at older units, the differences will be more pronounced, particularly with emissions and fuel economy. So if you’re considering an older 2-stroke model, make sure it has direct fuel injection, because a carbureted motor may struggle to pass emissions regulations.

Finally, think about the resale value of the unit. Will it hold its value or will it be difficult to sell in a few years’ time? Factor in whether the boat itself is light or heavy; whether you use it for fishing or watersports; and whether your trips tend to be short hops or day-long trips and you’ll have a clearer picture of the type of outboard motors better suited for your needs.