Are Two-Stroke Engines Better Than Four-Stroke Engines?

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Updated 11:22 AM ET, Mon July 6, 2015

Article highlights

  • Two-Strokes are less expensive and easier to maintain than Four-Strokes.
  • Two-Strokes are typically lighter but louder, while Four-Strokes are heavier but quieter.
  • Two-Strokes have faster acceleration while Four-Strokes have smoother rides.
Since Honda first introduced the Four-Stroke Outboard engine to the marine industry for consumers in 1964, the debate about Two-Stroke versus Four-Stroke has been ongoing for many years. Depending on your perspective, environmental concerns, improved technology, and your intended use, maybe there is no debate to be had.

Are Two-Stroke Engines Better Than Four-Stroke Engines?

Birth Of A Two-Stroke Engine


The first Outboard Engine was invented around 1870 by Gustave Trouve, a French electrical engineer and inventor. In 1907, Ole Evinrude invented the first practical and reliable Outboard Engine. Then a short two years later he founded Evinrude Motor Company in Milwaukee, Wisconsin. Until sometime in the late 1990's these Two-Stroke engines used carburetors to control the fuel-air mixture. Carburetor outboards are not particularly efficient, they use a lot of fuel, and can be cantankerous to creatures at times. These Two-Stroke engines required a gas-oil mixture in order to lubricate the internal working parts of the Engine.

Why Did The Original Two Strokes Retire?


As people complained about the smoke, pollution, noise and other side effects of the Two-Stroke engine, the Environmental Protection Agency (EPA) began imposing mandated requirements (Emission Standards) for Outboard Engines. These mandates sent the engineers and designers back to the drawing board striving to improve the efficiency and performance of the Two-Stroke engine. Most of the traditional, bigger Two-Strokes have been retired and replaced, by state-of-the-art, direct-injected Two-Strokes and fuel-injected Two-Strokes.

What Is A Two-Stroke Engine?


Direct-Injected Two-Stroke engines have separate Intake and Exhaust passages that are opened and closed by the piston skirt, as it pumps up and down in its cylinder bore. The benefit of this compared to the older conventional Two-Stroke is, no fuel wafts into the combustion chamber to inadvertently spill out into the exhaust port. Have you ever noticed the sheen on the water around your older running Two-Stroke engine? That is the gas-oil mixture that escaped through the exhaust port. With direct-injection however, fuel injects directly into the combustion chamber at the precise moment and with the precise amount required. These direct-injected engines use a computerized system to precisely regulate the fuel-air mixture to suit the operating conditions. That results in amazing performance gains as well as great fuel economy and low emissions.

Some Benefits Of A Two-Stroke


A direct-injected outboard engine has neither crankcase oil or use oil filters. Instead a precisely metered stream of oil lubricates rings and bearings, flashing off the combustion chamber, then exits along with the exhaust gas. Benefits of direct-injection are improved fuel efficiency, reduced emissions, oil usage, noise levels and maintenance needs.

Typically the Two-Stroke engine is lighter than a similar-sized Four-Stroke engine because the Two-Stroke method of operation does not require a valve train. The valve train consists of camshafts, valves, belts or chains. A Two-Stroke engine can often accelerate faster and have a better top end performance than the same horsepower Four-Stroke.

What Type Of Fuel System Does A Two-Stroke Have?


These direct-injected Two-Stroke engines are commonly referred to as DFI (Direct Fuel Injection) or HPDI (High Pressure Direct Injection) Outboard engines. Mercury Optimax, Evinrude E-TEC, Nissan TLDI and Yamaha HPDI engines are all direct-injected, yet each brand boasts a proprietary method for shooting a plume of vaporized fuel directly into the combustion chamber. What these varying methods have in common is the way high-pressure injection shatters the fuel charge into micron-size droplets exposing a greater surface area to oxygen. The burn is cleaner, so naturally it allows a greater volume of gasoline to be converted to BTUs. More BTUs released per gallon of gas equals better mileage and drastically reduces exhaust emissions. When the on-board computer reacts to a helm command, fuel injects instantaneously into the fire, instead of waiting for a vacuum to draw it in. This results in an almost immediate throttle response.

What Is A Four-Stroke Engine?


Four-Stroke Outboards use an engine very similar to an automobile engine. The air-fuel mixture flows into the combustion chamber through intake valves, and the exhaust leaves through the engine via exhaust valves. Because of these intake and exhaust valves (valve train); a Four-Stroke outboard engine is usually heavier than a Two-Stroke outboard of the same horsepower. As technologies continue to improve, Four-Stroke manufacturers are pursuing new ways to lighten the engines and extract more horsepower.

How Does A Four-Stroke Fuel System Work?


A Four-Stroke engines lubrication system is like a car's, complete with oil pan and filter. The additional components that make up a Four-Stroke engine, complimenting the cylinder heads are valves, springs, shims, keepers, valve lifters, camshafts, timing gears, belts and a crankcase. The majority of four-stroke engines feature sophisticated computer engine management systems and fuel injection. This provides for good performance across the power band, low emissions, and unparalleled fuel economy. Most Four-Stroke engines are fuel-injected as opposed to direct-injected, however some of the smaller horsepower Four-Stroke engines are carbureted. Four-stroke fuel injection is modeled after the sophisticated multi-port systems (MPI) found on cars and motorcycles. With one injector per cylinder strategically positioned near the intake valve, fuel injected Four-Stroke engines boast particularly swift throttle response.

Why Are Four-Stroke Engines Heavier?


Four-stroke engines tend to weigh from 10 percent to 20 percent more than an equivalent Two-Stroke direct-injected engine. This weight differential can adversely affect handling to the point that some boat builders have modified older hulls to keep up with the times. Six cylinder engine can add as much as 50 - 100 pounds additional weight,

Putting aside the technical differences between Two-Stroke and Four-Stroke engines, at lower rpm direct-injected Two-Stroke engines are more potent performers. They boast a power stroke with every swing of the crank. Four-stroke engines only build power on every other up and down swing of the crank. This difference is often compensated for by incorporating a lower gear ratio in the gear case. The lower the ratio, the more torque is multiplied, narrowing the gap between Two and Four-Stroke engines.

What Type Of Fuel Economy Does A Four-Stroke Have?


Fuel economy on both direct-injected and fuel-injected Four-Strokes ranges from 10 to 80 percent improvement over the older original Two-Strokes. Depending on rpm and load at cruising speed, figure about a 30 percent mileage improvement.

Some of the Pros and Cons you should consider before deciding on a Two-Stroke or Four-Stroke Engine are:

Two-Stroke Outboard Engines


Pros


Lighter
Faster
Less Expensive
Easier Maintenance
Parts Availability
Established Track Record
High Resale Value, High Demand

Cons


More Pollution
Smoke
Must Mix Gas with Oil (Non-Oil Injection Models)
Rougher Idle than Four-Stroke Engines
Carburetors gum up if not used often
Noisier than Four Stroke Engines
Spark Plug Fouling

Four-Stroke Outboard Engines


Pros


Quiet and Smooth
Good Fuel Economy
Great Trolling Motors
No Oil-Gas Mixture
Smooth Idle
Less Pollution
Very Reliable
Accepted on all bodies of water

Cons


Heavy
Can be expensive to repair
More parts to malfunction
Expensive to purchase

How Do You Intend To Use Your Boat?


Intended use of your boat can also influence your decision on whether to go with a Two-Stroke or Four-Stroke engine. With the ever increasing trend pulling away from using products that pollute our environment, and since more inland lakes are placing restrictions on the type of propulsion allowed, Four-Stroke engines are the only propulsion option. Will your intended use be strictly pleasure? Then either direct-injected Two-Stroke or fuel-injected Four-Stroke engines will meet your needs. It then comes down to cost, and what your budget allows.

If fishing is your passion, your boat and outboard engine are simply the means to get where the fish are and the outboard engine is the driving force behind the boat. So which is better in this instance, Two-Stroke or Four-Stroke? The answer is, it depends. If you are an inshore tournament fisherman you want an outboard engine that will get the boat up on plane quickly and maximize top-end speed to get to the honey hole before your competition. In this case a Two-Stroke Outboard Engine might best fit your needs.

Fishing situations where long periods of idling are required or when you are in fishing grounds that require long distances to travel to find the fish, this calls for an engine that is quiet and stingy on fuel. A Four-Stroke Outboard Engine would serve you well here.

What Kind Of Boat Do You Have Or Want?


The kind of boat you have can also dictate your choice in engines. A smaller boat may not be able to handle the additional weight of a Four-Stroke outboard. If your boat is larger, say greater than twenty something feet then a Four-Stroke might be in your future.

Here Is The Bottom Line


Fuel economy and speed are comparable between direct-injected Two-Stroke engines and fuel-injected Four-Stroke engines. Two-strokes tend to weigh less and can accelerate faster while Four-Strokes tend to be quieter with more toque than Two-Stroke outboard engines.

Now you have a better idea which is the best option for your boat!
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You need to do more research before publishing these articles. The new Evinrude E-TEC engines have overtaken all four stroke engines with 15-20% fuel mileage, 75% less pollution, within 3dba of sound output, major upgrades in mounting hardware and vibration isolation. As far as torque which is what drives a boat through the water, not horsepower, Evinrude E-TEC technology again leads the way with up to 35% more torque. Look up "The plane truth" on YouTube. A 200 HP Yamaha struggling to go 10mph when a 150 Evinrude pushes the boat to 30mph. The cool thing is that both motors are mounted to the same transom! It is interesting to learn dirty 4 stroke technology almost ended via the EPA 2020 regulations. The 4 stroke manufacturers all filed hardships that it would be too burdensome for them to meet the new regs while the Evinrude E-TEC outboards nearly meet these stringent standards now. While it may be acceptable to spout the erroneous facts as you have in this article if posting to blogs, etc., it is very disappointing for you to come off as some expert stating facts that will mislead the public with your incorrect information. Please update your article. Thank you.

David P. from United States, posted on FEB 12
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