2-Stroke vs 4-Stroke Engines: What's the Difference?

2-Stroke vs 4-Stroke Engines: What's the Difference?
Image: refer to hsw

About This Quiz

What's more powerful - a two-stroke engine or a four-stroke engine? Think you know? Prove your engine expertise by acing this quiz!

So, let's start with the basics. All engines have pistons that perform a specific number of strokes to complete a power cycle. Four-stroke engines complete the cycle with four strokes (two up-and-down motions) of the piston, resulting in two revolutions of the crankshaft. Two-stroke engines complete the cycle with two strokes of the piston (one up-and-down motion), resulting in one revolution of the crankshaft. Two-stroke engines get the job done with fewer parts and are therefore lighter, which in turn makes the engine more efficient.

Because two-stroke engines are lighter, they are perfect for smaller gasoline engines, such as those used in lawnmowers, chainsaws and even model airplanes and motorcycles. But even when the weight factor does not come into play, two-stroke engines are more efficient, making them ideal for many applications. Even if you aren't particularly familiar with the difference between a two-stroke engine and a four-stroke engine, you'll know that you're operating a two-stroke engine when you are required to mix the fuel and the oil together.

So, you think you know enough about engines to ace this quiz? Let's get started.

Oil change Two-stroke engine oil is also known as …
Two-cycle oil
Two-cycle oil is used in many small engines, from boat motors to chainsaws.
Two-piston oil
Two-inlet oil

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Modern Car Engine Compared to four-stroke engines, two-stroke engines tend to have what?
Longer lives
A good power-to-weight ratio
They're often used in small power tools and light vehicles because of their excellent power-to-weight ratio.
Better functionality

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car key in ignition lock What kind of ignition do most two-cycle engines use?
Spark ignition
Gasoline ignition is especially common in the smallest two-stroke engines.
Compression ignition
Neither

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car service True or false: Two-stroke engines typically don't last as long as four-stroke engines.
True
Their inefficient oiling methods mean less effective lubrication shorter engine life.
False

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Car mechanic replacing and pouring fresh oil into engine at maintenance repair service station Compared to lubricating oil, two-cycle oil has less …
Mercury
Carbon dioxide
Ash
Less ash makes burning the oil a bit cleaner.

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car service True or false: Compared to four-stroke engines, two-stroke engines have a shorter service life.
True
To maintain their working life, staying on top of lubrication is especially important in two-stroke engines.
False

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Repair man working in garage on repair When compared to four-stroke engines, how many parts do two-stroke engines contain?
Fewer parts
The lower number of parts in a two-stroke engine is the primary reason they tend to be lighter.
More parts
The same number of parts

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car spark plugs on engine How many times does the spark plug fire for each revolution of the crankshaft in a two-stroke engine?
Three times
Two times
One time
It only fires once per revolution. This trait helps two-stroke engines produce more power, by weight, than four-stroke engines.

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Auto mechanic examining overheated car in a workshop What color is the smoke emitted from many small two-stroke engines?
Blue/gray
It gets its blue tint from the oil that's blended into the fuel.
Brown
White

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Traffic jam True or false: You usually get more miles per gallon on a two-stroke engine than on a four-stroke engine.
True
False
At smaller sizes, two-stroke engines aren't really fuel efficient.

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boat's outboard motor and propellers Why are two-stroke outboard engines (for boats) NOT environmentally friendly?
Oil leakage
These engines can leave clouds of smoke and trails of oil in the water.
Coolant leakages
Friction problems mean higher emissions

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Car salesman showing engine to customers What is a primary inovation of the new two-stroke engine that Honda unveiled in 2015?
It uses extra cylinders.
It uses direct fuel injection.
The point of the direct fuel injection is to reduce the amount of unburned fuel in the emissions, making them run cleaner.
It has a new ignition technology.

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Powerful car engine What is the name for the upward stroke of a two-stroke engine?
Exhaust
Compression
The upward stroke is the compression stroke, and the downward stroke is called the power stroke.
Combustion

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Motorcycle engine close-up detail background What characteristic is typical of a two-stroke motorcycle's power band?
It is very narrow.
The range of RPMs that offer peak power on these bikes, known as the power band, occurs in a very limited range.
It is very wide.
It is the same as any other motorcycle.

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Auto Repair Garage with Mechanic, Torque Crankshaft Main Bearings Dugald Clerk's two-stroke engine was the first to do what during every revolution of the crankshaft?
Self-oil using a discrete oil tank
Self-correct for vibration from the pistons
Combine compression with ignition
It combined compression with ignition during each revolution. Clerk succeeded where other inventors had already failed.

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work on car engine What is another name for the oil/gas mixture in a two-stroke engine?
Kerosene
Petroil
Petroil, or two-stroke oil mixed with gasoline, makes the total-loss oiling system work.
Gas

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Close-up of muscle car engine compartment What is a typical compression ratio for a small four-stroke engine?
12-to-1
The typical compression ratio is 12-to-1. Higher compression ratios generally mean more power.
16-to-1
20-to-1

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Sports car exhaust In a two-stroke engine, at the start of a new stroke, both the inlet and exhaust ports are …
Open
They are both open. Air pressure differences cause a fresh fuel/air mix to move into the combustion chamber.
Closed
Partially closed

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Ship's engine room Compared to four-stroke engines, how efficient are the enormous two-stroke diesel engines used on ships?
They are far less efficient.
They are far more efficient.
It seems bigger really is better when it comes to the efficiency of two-stroke engines.
They are about the same.

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Engine crankshaft How many revolutions does the crankshaft make during a power cycle in a two-stroke engine?
Six
Four
One
The crankshaft, which converts the pistons' up-and-down motions into rotation, makes one complete turn each power cycle.

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US patent application What year was the first two-stroke engine (with in-cylinder compression) patented?
1781
1881
Dugald Clerk invented it in Scotland and patented his creation in England in 1881.
1913

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Mechanic working under car in car dealership workshop holding torch What's an advantage of a rotary valve?
It makes asymmetrical engine timing possible.
Asymmetrical engine timing often results in better power output.
It lowers noise levels.
It improves lubrication.

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Biker on adventure motorcycle ride Who created the first practical two-stroke motorcycles?
Wilhelm Maybach
Sylvester Roper
Alfred Scott
Scott, who also had about 50 other patents to his name, founded the Scott Motorcycle Company in 1908.

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Mechanical engineer use computer check and programming to tune car after repair in the service shop How many strokes do two-cycle engines require to complete a power cycle?
Two
Two up-and-down motions make up the stroke (and the power cycle).
Four
One

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nozzle fuel for fill oil into car tank at pump gas and oil station with technology icons concept design For small two-stroke engines, approximately how many ounces of two-stroke oil do you need per gallon of gas?
2 fluid ounces
4 fluid ounces
You need 4 ounces of oil per gallon of gas — and it can be pricey, too.
8 fluid ounces

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Car mechanic is changing engine oil In small two-cycle engines, where does the oil originate?
Oil sump
Carburetor
The oil originates in the carburetor and, from there, is mixed directly into the fuel.
Neither

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Washing the Car and inspect engine compartment for trouble What is the most common type of inlet port on smaller two-stroke engines?
Rotary
Reed
Piston-controlled
In this configuration, the piston covers and uncovers the ports as it travels up and down the cylinder. The 1970s saw significant improvements in piston-controlled inlet ports.

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Engine cylinder What is a typical compression ratio for a small two-stroke engine?
2-to-1
6-to-1
The 6-1 compression ratio, which means the volume of the mixture is compressed by the piston in the cylinder to one-sixth of its original, is fairly low for small engines.
10-to-1

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Check the oil in Car Engine How do the lubrication systems on large two-stroke engines work as compared to large four-stroke engines?
They are very similar.
The oil-fuel mixing process is mainly for smaller and cheaper two-stroke engines.
They are completely different.
As with smaller two-stroke engines, you're required to add oil to the fuel.

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Modern powerful car engine Compared to four-stroke engines, what are the characteristics of emissions from small two-stroke engines?
They are the same.
Two-stroke engines are a little cleaner.
Two-stroke engines emit dirtier exhaust.
The emissions are higher in large part due to the oil that's mixed with the gasoline.

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