What Is the Difference Between a 4-Stroke and 2-Stroke Engine?

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What is engine stroke?

Most newer cars, trucks and SUVs have engines that are very fuel efficient. In order for any engine to work correctly, it must complete the combustion process, which includes four individual strokes of the connecting rod and piston inside the combustion chamber in a four-stroke engine, or two for the two-stroke engine. The primary difference between a two-stroke engine and a four-stroke engine is the timing of firing. How often they fire tells you how they convert energy and how quickly it occurs.

To understand the difference between the two engines, you must know what a stroke is. It takes four processes to burn fuel with each process comprising one stroke. Listed below are the four individual strokes that are involved in the four-stroke process.

  • The first stroke is intake stroke. The process of operating an engine begins with the intake stroke, where the piston is pulled in a downward direction. This allows a mixture of fuel and air to enter the combustion chamber through the intake valve. During the starting process, power to complete the intake stroke is supplied by the starter motor, which is and electric motor attached to the flywheel, which spins the crankshaft and moves each individual cylinder.

  • The second stroke is compression. A they say, what goes down, must come up. This is what happens during the compression stroke, which occurs when the piston moves back up the cylinder. During this stroke, the intake valve is closed, which compresses the stored fuel and air gases as the piston moves towards the top of the combustion chamber.

  • The third stroke is combustion. This is where power is created. Once the piston reaches the top of the cylinder, the compressed gases are ignited by the spark plug. This creates a small explosion inside the combustion chamber which forces the piston back downward.

  • The fourth stroke is exhaust. This completes the four-stroke combustion process, as the piston is pushed back upward by the connecting rod, while the exhaust valve opens up and releases burnt exhaust gases out of the combustion chamber.

The stroke is considered one revolution – so when you hear the term Revolutions Per Minute, this means that it’s one complete engine cycle – or four individual strokes per revolution. So, when an engine is idling at 1,000 RPM, it means that your engine completes the four-stroke process 1,000 times per minute, or about 16-times per second.

The differences between two-stroke and four-stroke engines

The first difference is the fact that the spark plugs fire once every revolution in a two-stroke engine, and fire once every other revolution in a four-stroke engine. A revolution is one set of four strokes. Four-stroke engines allow each stroke to happen independently. A two-stroke engine requires the four processes to occur in a downward and upward stroke, which gives the two-stroke its name.

Another difference is that two-stroke engines don’t need valves because intake and exhaust are part of the compression and combustion of the piston. Instead, there is an exhaust port in the combustion chamber.

Two-stroke engines don’t have a separate chamber for the oil, so it must be mixed with the fuel in proper amounts. The specific ratio depends on the vehicle and is found in the owner’s manual. Two of the most common ratios is 50:1 and 32:1 with the 50 and 32 referring to the amount of gasoline to one part of oil. A four-stroke engine has a separate compartment for the oil and doesn’t require mixing. This is one of the easiest ways to tell the difference between the two types of engines.

Another method of identifying the two is by the sound. Two-stroke engines are often loud with a high-pitched buzz, while a four-stroke engine emits more of a soft humming noise. Two-stroke engines are often seen in lawnmowers and performance off-road vehicles (like motorcycles and snow mobiles), while four-stroke engines are what you’ll find powering on-road vehicles and high performance large displacement engines.


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Mario

18 years of experience
103 reviews
Mario
18 years of experience
Honda Prelude - 75 Point Safety Inspection - Fort Myers, Florida
on Arrival he introduced himself. Extended his hand with a warm and welcoming shake as he addressed me my name. Mario got right to work. He looked at everyThing under the hood. Then he Showed me and explained The discoveries that needed attention and repairs. He is soKnowledgeable and veryCourteous. I will beUsing Mario for all the needs, repairs for/to my Honda Prelude. I highly recommend Mario! He is an ace!!!
Dodge Avenger - 75 Point Safety Inspection - Fort Myers, Florida
I scheduled for work to be done to replace my vehicle's serpentine belt, pulley, and tensioner ('cause Firestone said that it needed to be "replace"). When Mario arrived and checked the belt, he was very honest and informed me that the serpentine belt did not need to be replaced. He showed me the serpentine belt and pointed out that it did not have any cracks. It didn't need to be replaced for "preventive maintenance" either. I appreciate his honesty and the time that he took to show me other issues (that Firestone failed to mention) and explained it.

Duane

23 years of experience
378 reviews
Duane
23 years of experience
Toyota Prius - 75 Point Safety Inspection - Carlsbad, California
Duane performed diagnostics and isolated the real problem which was different than my determination. He performed only the tasks required. Very competent and honest.

Estevan

10 years of experience
28 reviews
Estevan
10 years of experience
Toyota Camry - 75 Point Safety Inspection - Riverside, California
Estevan was very polite, friendly, and helpful! He called to let me know it would take a little extra time to get the part I (thought) the car needed. When it turned out to be something else, he happened to have the materials on hand to do a speedy fix. The service included an inspection and a list of recommended other items of concern, but at no point was he pushy about the other suggested services. A+, highly recommended!

Jerimiah

17 years of experience
328 reviews
Jerimiah
17 years of experience
BMW 528i - 75 Point Safety Inspection - Las Vegas, Nevada
Fantastic....There is a lot of work needed. He informed me that I needed work done on my control arm which was replaced in Dec 2018 by Big O Tires. Not sure how long they should last but I am pretty sure that I can get atleast a year. They replaced them(supposedly), but the issue continued after. Anyway, I am glad that Jeremiah pointed this out. Thank

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