If you were drawn here by wondering what the differences are between 2-stroke and 4-stroke engines, you’re in the right place! I’ll walk through a few crucial points about go-karting and its relationship with engines.
So, what is the difference between 2-stroke and 4-stroke engines? 2-stroke engines tend to be more prevalent in sprint karting due to their light weight and rapid acceleration, while 4-stroke engines feature prominently in endurance karting due to their fuel efficiency.
There are obviously far more differences, pros and cons to be weighed up with both of these engines, and I’ll go into those after explaining the science of an engine. Knowing how something works makes it far easier to look at that contraption, after all!
How Engines Work
Combustion engines all work the same, from go-karts to road cars. Like I mentioned above, it’ll get easier to see the difference between 2-stroke and 4-stroke engines if you understand how an engine works in its most basic form.
To get power and start moving, the piston within the engine’s cylinder needs to be going up and down. Specifically, the piston needs to hit two distinct points in said cylinder to properly allow air flow and therefore get combustion to happen for the go-kart or other vehicle to get going.
These two points are abbreviated to TDC (“top dead center”) and BDC (“bottom dead center”). As you can probably guess from what each means, TDC is the point nearest the top of the cylinder where the valves are located, and BDC is the position which is furthest away from these valves.
A stroke is when the piston moves from TDC to BDC, and vice versa, which is how engines are named. It’s based on how many of these strokes are needed to make a complete combustion cycle, which is broken down below:
- Intake: The piston first moves down the cylinder which allows a mixture of fuel and air into the combustion chamber
- Compression: The piston moves back up the cylinder and the intake valve is closed to compress the gasses
- Combustion: A spark from the spark plug ignites these gasses, pushing the piston down
- Exhaust: The piston goes back up the cylinder and the exhaust valve is opened
With that general overview out of the way, let’s look at how this applies to both 2-stroke and 4-stroke engines, shall we?
2-Stroke Engine Primer
Typically, you’ll see 2-stroke engines on lawnmowers, weed-whackers and even on toy planes, which all points to one thing: these engines are amazingly lightweight!
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Although the size of the engine will differ, it’s the lack of extra components that make it not only very simple to repair if things go wrong, but also keeps it very light when compared to other engines.
This is because the piston in a 2-stroke engine acts as multiple parts of the combustion process. It transfers force within an engine, compresses the gas within, intakes gas and expels the byproducts; achieving all of this by simply moving back and forth. Who needs four components when one will do everything you need it to?
For every rotation of the crank shaft which propels the piston, the spark plug fires off and produces that explosive propulsion for the engine to gain its power. Due to the streamlined nature of this engine, you must mix your fuel and oil together, because all of the components are contained in the same area; that intrinsic, all-important piston.
4-Stroke Engine Primer
Whereas a 2-stroke engine has a single piston doing all of the work, a 4-stroke engine has multiple pistons performing different functions.
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Most engines of this type have four pistons working together. One set of two pistons takes care of the compression stroke while the other set deals with the exhaust stroke, followed by the return.
This process requires two rotations of the crank shaft to complete the combustion process, which leads to the spark plugs firing once every other revolution and power is generated every fourth stroke of the piston.
There are a lot more parts involved in this process, with pistons having different functions and the work being spread thinner than the single piston in 2-stroke engines.
This type of engine is most commonly seen in larger devices that require propulsion, and is even seen in normal road cars. Due to the higher complexity of this engine, you will find a separate compartment for oil to be deposited for parts of the machine to stay properly lubricated during this combustion process.
While describing each type of engine, I unwittingly mentioned a few distinct differences simply because it’s these that set the types of engine apart.
It’s common to explain the function of a 4-stroke engine by explaining how it needs a further crank rotation compared to a 2-stroke, for example. I’m going to lay out some more differences below, with a view of being more specific:
- Efficiency: The 4-stroke engine wins in this regard, because it only intakes fuel once every four strokes. Less fuel being consumed means that the engine can be powered for longer!
- Weight: Because 4-stroke engines have more pistons, a longer/ heavier crankshaft and a cam shaft with multiple spark plugs, it goes without saying that they’re weightier than the simpler, smaller 2-stroke variant. After all, a 2-stroke engine possesses a single piston and one spark plug to perform the whole combustion cycle.
- Durability: As with anything that has a great deal of pressure put on its parts, 2-stroke engines are more likely to encounter wearing/ breakages when compared to a 4-stroke engine.
- Power: When comparing each engine in terms of their raw power output, the 2-stroke engine is the winner of the pair. It combusts far more frequently than the 4-stroke, and that means more frequent, responsive power!
- Maintenance: More parts means more to fix and of course, being more complicated to fix if things go wrong, which makes the 4-stroke the more complex of the pair. 2-stroke engines are lacking in parts and complex sets of extra valves, so they’re easy to perform regular maintenance on.
- Environment: Because you aren’t mixing oil with fuel, the 4-stroke engine is considered to be more environmentally friendly than its 2-stroke counterpart. That, and the 4-stroke is also considerably quieter than the distinctive buzz-like roar of a 2-stroke engine.
Engines In Practice: What This Means In Go-Karting
So, now you know how engines work in a basic sense, what 2-stroke and 4-stroke engines are, and how the two engine types differ from one another. Although some practical applications stand out from my explanation of how the engines differ, I’m going to spend some time to explain which engines are better in go-karting specifically.
Because 2-stroke engines generate more power more frequently than their 4-stroke counterparts, and they’re also far lighter, you’ll see a lot of these engines on go-karts. The fact that 2-strokes are also very easy to maintain, with a lack of complicated parts to worry about also makes them very attractive to go-kart enthusiasts.
Most, if not all, go-karts in younger age brackets have a 2-stroke engine installed, and this is because kids are lighter than adults. Lighter load, plus a lightweight, smaller kart, wrapped up with a 2-stroke and you’ve got a winning package!
That isn’t to say that you won’t see these engines on adult karts; rental tracks will use a couple of 2-strokes to power their rigs because of how easy they are to maintain. It doesn’t really matter that the 2-strokes aren’t very efficient because in sprint kart races, you’ll only be doing a maximum of 30 laps on most circuits.
For karts that spend more time on the track in longer races, a trusty 4-stroke will almost always be attached. The extra weight onboard doesn’t make such a huge impact when you want to run a long race, because you won’t be hugely concerned about speed alone.
Although 4-stroke engines take more time to maintain and are generally more complicated to look after, they are generally more reliable. All of these factors make them a favorite for endurance racers. If you couple a 4-stroke with a clutch/ gear system, although this adds more weight to the rig, you’ll also reach a higher top speed potential.
This is because the engine can match the gear input of the driver and will work harder when needed, outputting that further torque which is needed for overtakes or other such maneuvers. You’ll almost always see shifter karts with a 4-stroke engine on-board for this very reason!
As with anything in life, differences within something can become a huge advantage depending on what you’re looking at.
If you’re wanting to get a kart for your little one, a 2-stroke engine is a no-brainer, similarly if you want to take part in quick sprint events in your own rig.
But if you’re keen for more reliability and efficiency for endurance races, the 4-stroke is right up your alley.
One engine isn’t objectively better than the other, because it solely depends on what each one is being tasked to do. Strapping a 2-stroke onto a shifter won’t get you anywhere, and attaching a 4-stroke to a kid’s kart will see you lagging behind.
With all of that being said, make sure to use this newfound engine knowledge to better your karting experience! Or use it during bar talks to flex just how much you know about things that go fast; both being equally important, of course!