2- Vs. 4-Cycle Outboard Motors
April 16, 2018
Whether you're buying a new boat or re-powering your favorite fishing platform, you face a number of decisions—perhaps the biggest of which is whether to purchase a 2- or 4-stroke outboard.
The battle between these two engine designs is long running, and the differences used to be dramatic. Like loud, obnoxious fishing partners, screaming 2-strokes guzzled gas and spewed blue smoke. Prone to rough idling, they fouled plugs and gummed carbs with a vengeance. Still, 2-strokes were powerful allies, capable of rocketing your boat onto plane and getting to the next honeyhole in a hurry.
Four-strokes, on the other hand, were well-mannered, gentle giants—quiet, easy on fuel, and able to cruise or troll long distances (even at low idle) without a misfire. On the downside, 4-strokes could be cumbersome, heavy for their horsepower, and slower out of the starting gate.
Technological gains in both categories have blurred some of the lines in recent years, giving shoppers plenty to think about when tendering the remaining tradeoffs. Which is why, now more than ever, understanding each category's strong suits is critical to choosing a powerplant that best fits your personal needs and preferences.
As its name implies, a 2-stroke engine accomplishes the necessary functions of intake, compression, transfer/exhaust and power with just two strokes of the piston (a stroke being defined as the piston's full travel within its cylinder, in either direction).
A 2-stroke engine relies on both the cylinder and crankcase to make this happen. It also multi-tasks: the end of combustion and start of compression strokes occur simultaneously, while intake and exhaust happen at once.
Due to this design, a 2-stroke fires on every revolution of the crankshaft. The concept makes for simple, lightweight and powerful engines with fewer moving parts than 4-stroke motors. On the downside, the 2-stroke design is also inefficient, noisy and heavy on emissions.
For its part, a 4-stroke engine requires four strokes of the piston to complete a power cycle. The four strokes are intake, compression, power and exhaust. Although the 4-stroke requires twice as many piston strokes and turns of the crankshaft to generate power, it is extremely fuel efficient, quieter and produces far fewer emissions.
Two-strokes long held the advantage in blistering acceleration and fast hole-shots (getting the boat onto plane). Today, however, modern 4-strokes and the boats designed to run with them make the speed race virtually a dead heat.
Some 4-stroke manufacturers push performance even farther. For example, Honda Marine leaned on its extensive automotive expertise to create Variable Valve Timing and Lift Electronic Control (VTEC) technology, which varies the lift and duration of the intake valves for a broader, flatter torque curve that yields an impressive blend of power, torque and efficiency from idle to full throttle.
Sounds of Silence
Four-stroke outboards have long held the advantage in quietness, whether idling or running at high RPMs. When 4-strokes first hit the market in force, anglers welcomed the opportunity to converse with boatmates while under power, without shouting at the top of their lungs.
In fact, 4-stroke silence was such a departure from the raucous behavior of 2-stroke engines, it wasn't unheard of for boaters to forget a new 4-stroke outboard running after docking their vessel, or even when pulling their boat from the water.
Today, 4-strokes remain up to 50 percent quieter than most 2-stroke engines. Still, 2-strokes have improved to the point that some new models actually hold a slight sonic advantage over their 4-stroke counterparts. Decibels can be deceiving, however. Four-strokes resonate a pitch more pleasing to human auditory nerves, which makes their subtle hum less of a distraction from the overall boating experience than the whine of a 2-stroke.
Fuel And Oil Economy
Score another point for 4-strokes, which are approximately 50 percent more fuel-efficient than typical 2-stroke outboards. To be fair, advanced 2-strokes have narrowed the gap and in cases, when paired with specific boats or running conditions, can give 4-strokes a run for their money.
On the oil front, 4-strokes dominate. A 4-stroke typically requires an oil change once a year, making the chore and its price tag a fixed annual cost. For example, a V-6 Honda 225 or 250 holds 8 quarts of oil—meaning that's all the oil you use in 12 months, no matter how many hours you put on the engine.
Two-strokes, conversely, require oil to be continually mixed with the fuel. New outboards do the mixing for you, but you still need to keep the oil— reservoir flush with pricy fluid that costs $40 or more per gallon. At a 100:1 oil-to-fuel ratio, you'll burn $40 or more worth of oil for every 100 gallons of gasan expense that quickly adds up, especially when extensively running larger 2-strokes.
Durability And Reliability
While 2-stroke engines rely on gas or air to deliver protective oil to critical components, a 4-stroke motor's internal parts are bathed in oil. Along with consistent lubrication, this design also helps cool engine components, further boosting durability.
As a bonus, because 4-strokes don't rely on fuel for lubrication, manufacturers like Honda Marine engineer their engines to reduce fuel consumption by automatically running a leaner air-fuel mixture when not under heavy load. Do that with a 2-stroke and you're flirting with disaster.
It's also worth noting that the ports in 2-stroke cylinders and pistons can accelerate ring and piston wear. Because there are no intake or exhaust ports in a 4-stroke cylinder or piston, they can operate with tighter tolerances for longer engine life.
Such durability boosts reliability. But also consider where the engine's technology came from. The high-tech designs and components of advanced 2-strokes are often relatively new and untested compared to the automotive technology that drives many modern 4-strokes. For example, the inner workings of Honda 4-stroke motors spring directly from a car or truck known for commercial-grade reliability over the long haul.
Thanks to ultra-low emissions, 4-stroke engines are up to 90 percent cleaner than typical 2-strokes. Plus, 4-strokes don't release oil directly into the water—a sin 2-strokes are prone to commit. Coupled with fuel savings, this makes 4-strokes the green machines of the outboard world.
Cost is a major factor for most anglers and boaters when choosing an outboard. However, engine price is rarely based on the number of piston strokes needed to spin the prop, as outboard motor prices vary more by manufacturer and model than 2- versus 4-stroke.
If you're tempted to shop by price tag alone, remember there's more to economics than initial purchase price. When comparison shopping, remember to factor in the cost of operation—including fuel, oil, routine maintenance and potential repairs—along with durability and resale value.
And don't forget the value of running an outboard that makes your boat perform exactly how you want it to, then reliably returns you to the dock after every excursion—which, as the saying goes, is priceless.