If you were drawn here by wondering what the differences are between the two most common types of kart engines, you’re in the right place! Whether you’re a beginner or a more experienced kart driver, it helps to understand where 2-stroke and 4-stroke kart engines vary.
2-stroke kart 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. 2-stroke engines are more used for kids, while 4-stroke engines are more advanced.
There are obviously far more differences and pros and cons to be weighed up with both of these engines. Below, I’ll go into those after explaining the basic science of a kart engine. Knowing how something works makes it far easier to look at that contraption, after all!
How Do Kart Engines Work?
Kart engines work like regular combustion engines do, in that the piston is the primary thing that powers them. It moves up and down in a cycle. This cycle starts with air and fuel going into the combustion chamber, then the gases get compressed, then ignited, and then finally exhaust is let out.
Combustion engines all work the same, from go-karts to road cars. As I mentioned above, it’ll be 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 the cylinder to properly allow airflow and therefore get combustion to happen for the go-kart or other vehicle to get going.
TDC & BDC
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 that 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 gases
- Combustion: A spark from the spark plug ignites these gases, pushing the piston down
- Exhaust: The piston goes back up the cylinder, and the exhaust valve is opened
Note: In a 4-stroke engine, each half-rotation - or stroke - of the crankshaft corresponds to one of these steps, while in a 2-stroke engine, each stroke performs two parts of the combustion cycleHow 2-Stroke Kart Engines Work
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!
Although the size of the engine will differ, it’s the lack of extra components that keeps it very light when compared to other engines and also makes it very simple to repair if things go wrong.
This is because each stroke in a 2-stroke engine performs multiple parts of the combustion process. One stroke compresses the gas within the cylinder and ignites it, while sucking in fuel and air into the crankcase. The next stroke expels the waste gases at the same time as it sucks in more fuel and air for the next stroke. Who needs four strokes when two will do everything you need?
Due to the streamlined nature of this engine, you must mix your fuel and oil together to provide both combustion and lubrication.
How 4-Stroke Kart Engines Work
Whereas a 2-stroke engine has just two strokes doing all of the work, a 4-stroke engine requires – you guessed it – four strokes. This process requires two rotations of the crankshaft 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, following the 4-step combustion process we outlined earlier.
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.
Key Differences Between 2-Stroke & 4-Stroke Engines
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 components, it goes without saying that they’re heavier than the simpler, smaller 2-stroke variant.
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 mean more to fix and, of course, they are more complicated to fix if things go wrong, which makes the 4-stroke the more complex of the pair. 2-stroke engines contain fewer parts and complex sets of extra valves, so they’re easy to perform regular maintenance on.
Environmental Issues
Because you aren’t mixing oil with fuel, the 4-stroke engine is considered to be more environmentally friendly than its 2-stroke counterpart, and it’s more fuel efficient. That, and the 4-stroke is also considerably quieter than the distinctive buzz-like roar of a 2-stroke engine.
2-Stroke vs 4-Stroke Karting Engines In Practice
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 now going to spend some time explaining which engines are better in go-karting specifically.
2-Stroke Engines In Karting
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 2-stroke 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 loads, plus a lightweight, smaller kart, wrapped up with a 2-stroke, makes for a winning package!
That isn’t to say that you won’t see these engines on adult karts. Rental tracks will often use 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.
4-Stroke Engines In Karting
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 the extra torque that is needed for overtakes or other such maneuvers. You’ll almost always see shifter karts with a 4-stroke engine onboard for this very reason!
Final Thoughts
2-stroke and 4-stroke kart engines hold some key distinctions that set them apart from one another. The former is lightweight, making it easier for kids in go-karting and for rental units. 4-stroke engines, which are used in cars, are the more reliable and efficient option of the two.