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

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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Pardeep

20 years of experience
721 reviews
Pardeep
20 years of experience
Ford Fusion - 75 Point Safety Inspection - San Jose, California
I have ordered a 75-point inspection of the car since my dealership claimed it had an oil leak and the timing cover replacement was due (this kind of repair costs in the ballpark of a thousand dollars). I mentioned the need for a second opinion on that since the car had been bought relatively recently from that dealer (certified pre-owned) and not very actively used. Pradeep performed the safety inspection in a very timely manner and addressed my main question by honestly concluding that there was no leak but just some dust collected over time. This has saved me much time and money. Finally, I was also very glad to learn a tip on how to find a matching paint for a body scratch from him.
Ford Escape - 75 Point Safety Inspection - San Jose, California
Pradeep immediately found the suspension problem I was worried about and fixed it. We had just purchased this car and now feel a lot better about it now that he has checked it out.

Honorio

18 years of experience
825 reviews
Honorio
18 years of experience
Hyundai Accent - 75 Point Safety Inspection - Sunnyvale, California
Honorio not only told me what is going on with the car but was so honest about everything. Looking forward to having Honorio taking car of my requests.
Acura RDX - 75 Point Safety Inspection - Palo Alto, California
Honorio went above and beyond my expectations. He was honest about which repairs needed to be done even though my service revision decreased his income. Will absolutely use again!!!! Thank you!

Collins

11 years of experience
199 reviews
Collins
11 years of experience
BMW 330xi - 75 Point Safety Inspection - Atlanta, Georgia
It was a good appointment. Collins came over and inspected my car but unfortunately was not able to install the driver's side axle. After his inspection, he told me that I needed a hub bearing assembly on that side and that my axel was in pretty good shape. He did not have the equipment pull the hub bearing for installation but he was very knowledgeable s we discussed that process. His inspection also revealed that my car was in need of a passenger's side CV axle assembly. I was only charged for his inspection fee and we agreed that I would call at a later time for the actual work to be done. This will have to take place after I have wheel bearing hub assemblies installed. I was informed that the company would credit my account for any unused fees that I paid.

Robert

21 years of experience
64 reviews
Robert
21 years of experience
Dodge Durango - 75 Point Safety Inspection - Fort Worth, Texas
Robert showed up ontime. He was very friendly, knowledgeable. I look forward to him completing my future repair.

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