How to Decide Between a Two- or Four-Stroke Outboard Boat Engine
July 25, 2011
When the time comes to repower Old Faithful or to spring for a new rig, what kind of outboard boat engine are you going to buy? Tough question, given the dozens of innovative choices from the various engine manufacturers.
One of the biggest decisions is whether to invest in a two-stroke or four-stroke engine. With the proliferation of misinformation regarding this subject, it's easy to confuse fact and fiction. Not to worry. We'll walk you through the fundamentals and add some clarity to the subject.
In a two-stroke engine, the fuel-air mixture enters the combustion chamber via a opening in the side of the cylinder. The exhaust exits through another port in the cylinder.
Initially, two-stroke engines used carburetors to control the fuel-air mixture. But carbureted outboards aren't particularly efficient. They also use a lot of fuel, and tend to be cantankerous creatures.
Today's top-of-the-line two-stroke engines use a computerized Direct Fuel Injection (DFI) system to precisely regulate the fuel-air mix to suit the operating conditions. That results in amazing performance gains as well as great fuel economy and low emissions.
Typically, a two-stroke outboard is lighter than a similar-sized four-stroke engine because the two-stroke's method of operation doesn't require a valve train -- camshafts, valves, belts or chains. Since the two-stroke isn't encumbered with a valve train, the engine has fewer moving parts. Thus, it has less rotating mass. A two-stroke outboard can often accelerate faster than the same horsepower four-stroke.
The engine's internal components receive lubrication from oil mixed into the fuel.
Contrary to popular belief, two-strokes aren't a dying breed. The fact is, carbureted two-strokes are going away due to their inability to comply with increasingly stringent emissions legislation. However, the DFI two-stroke outboards are thriving and remain popular.
Four-stroke outboards use an engine very similar to an automobile's. The air-fuel mixture flows into the combustion chamber through intake valves, and the exhaust leaves the engine via exhaust valves.
Because of these intake and exhaust valves (the valve train), a four-stroke outboard is usually heavier than a two-stroke outboard of the same horsepower. But, we see that changing: four-stroke manufacturers continue to pursue new ways to lighten the engines and extract more horsepower.
A four-stroke outboard's lubrication system is like a car's, complete with oil pan and filter -- and the engine needs periodic oil changes to keep things running smooth.
The majority of four-stroke outboards feature sophisticated computer engine management systems and fuel injection for good performance across the power band, low emissions, and unparalleled fuel economy.
CHOOSE YOUR OUTBOARD
From an angler's perspective, a boat is nothing but a means to get to where the fish are -- a fishing platform -- and the outboard is the driving force behind the boat. Tools of the trade, so to speak.
Taking that point of view, how do you pick the right outboard for your boat? Two-stroke or four-stroke -- the broad answer is, it depends.
It depends on how you fish, where you fish, what kind of boat, and how much gear you carry with you.
If you're a dedicated tournament angler, then you need an outboard that will pop the boat up on plane quickly and maximum top-end speed to get to the honey-holes before your competition does. In this case, a two-stroke might fill the bill nicely.
Fishing situations that require long periods of idling through no-wake zones, or pursuing bass in large impoundments where you'll need to go several miles to find the fish, calls for an engine that's quiet and stingy on fuel. A four-stroke could do well here.
The kind of boat also dictates the best engine. For example, every boat has a placard stating the boat's weight capacity; a smaller boat may not be able to tolerate the additional weight of a four-stroke outboard. On the other hand, if your rig is one of the newer mega-boats -- 21 feet plus, or if you fish alone and don't take a bunch of extra stuff with you -- then you can start looking at four-strokes.
A big boat or heavily loaded boat can benefit from the torque of a four-stroke outboard.
On the economic and practicality front, it's important to consider who is going to service the engine and be there for you to take care of any potential warranty issues. The type of engine that your local dealer carries is a major consideration in choosing your new outboard.
Your local dealer will often work with you and perhaps make you a better deal at trade-in time, in addition to being available when trouble rears its ugly head.
Fuel economy and speed are comparable between two-strokes and four-strokes. Two-strokes tend to weigh less but can accelerate faster. Four-strokes tend to be quieter and have more torque than two-stroke outboards.
Both technologies are solid and highly evolved. Each has advantages an disadvantages.
Now you have a better idea which is the best for the transom of your fishing boat.