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One specific debate seems to never end in the dirt bike community: which is better between two-stroke engines and four-stroke models.
When motocross was gaining popularity in the UK, four-strokes like Triumph and BSA dominated the scene although they were small populations that favored two-stroke machines.
Suzuki popularized the two-strokes in the late sixties and established decades-long domination of the models in world championships.
In 1993, Jacky Martens emerged victorious at the 500cc world championship with a four-stroke Husqvarna, a move that marked the beginning of the four-strokes. The 2000s were characterized by the mass production of all things four-stroke models, mainly from Japanese brands.
The fours now dominate the motocross landscape, mainly due to the increased capacity accommodated by the four-strokes. The two-strokes are primarily used in niche race series and junior classes.
A section of the dirt bike riding community has blamed the format of the AMA and big companies like Honda for the influence they have over major Championships races that specify the kind of bikes allowed to compete. The two strokes have also faced unpopular opinion because of the environmental damage they cause.
2 Stroke or 4 Stroke Dirt Bike for Beginners
Two strokes may be cheaper, but they are not necessarily better for dirt bike beginners. Four strokes are generally easier to handle.
When using a two-stroke, a rider will have to make a pre-mix for the bike in the right ratio of two-stroke oil and fuel. If the mixture is wrongly concentrated, the plug may end up being fouled.
2-strokes require a lot of rotations per minute (rpm) to generate power and to maintain the plug from getting fouled. Four strokes only need gas, and you are good to go. The risks of fouling the plug are lesser with 4-stroke engines.
Fuel mixture is also not as critical as with the two-strokes. 4-stroke engines give out more torque at lesser rpms and are thus the better fit for beginners. Basically, a 4-stroke engine lets you just focus instead of other things concerning the bike.
2 Stroke vs 4 Stroke Fuel Efficiency
When compared with a 4-stroke, a 2-stroke engine presents more fuel consumption. An amount of the air-fuel mix on a 2-stroke is lost via the exhaust opening on the upward piston stroke.
The four-stroke engines feature valves that open and close and which eliminate any air-fuel loss.
2 Stroke vs 4 Stroke Emissions
A 2 stroke-engine is generally less efficient because it has the exhaust pipe and the fuel intake opened at the same time. An amount of the fuel-oil mix escapes through the exhauster.
The four-stroke engine rejects a total loss lubrication system, which means that less oil is burnt during combustion. A lesser amount of unburnt fuel is therefore released via the exhaust pipe, making it more environmental-friendly.
2 Stroke vs 4 Stroke Dirt Bike Maintenance
There are about 30% to 50% fewer moving components on a two stroke-dirt bike vs. a four-stroke. The simplified system on the former model makes it much simpler to maintain and work on.
The four-stroke has more parts that need regular maintenance. The cost of rebuilding a two-stroke engine is also cheaper than that of a four-stroke.
The prospect of replacing all the moving components on the 4-stroke is enough to make some riders hesitate from the model. Riders are also less likely to strip down a 4-stroke engine by themselves, so there are the potential costs of paying a professional.
If you buy a quality 4-stroke model, however, it will likely serve you for several years of off-road use. You might require a piston replacement or need to evaluate the valve clearances occasionally, but it is still less than the maintenance you will need on a two-stroke engine.
A two-stroke might be easier to repair, but you will have to commit to regular freshen ups.
2 Stroke vs 4 Stroke Power
Two strokes may be a thing of the past when it comes to motocross tracks, but it does not mean that they cannot hold out their own on the trail. Four strokes only have the upper hand because of race guidelines regarding engine displacement.
To become competitive, the models literally doubled the level of displacement for what is allowed on 2-strokes. As the 4-stroke became more advanced over several years, it became clear that they performed better and sales increased dramatically.
On the track, the distinctions between the engines boil down to delivery. 2-stroke motorcycles hit hard and fast and leave an explosive impression on the person controlling it. Four strokes are less intense and give a rider more control.
For comparison purposes, pit a like against a like at a specific capacity. The results of running a 250cc 4-stroke against a 250cc 2-stroke engine will be quite interesting as the two-stroke will be more powerful.
Before power valves were installed on two-strokes, their power delivery was brutal. The hit would be delivered like a sledgehammer at the back of the rider’s head, and the landscape would blur. Power valves made the energy more manageable and modern two-strokes provide this power via the rev range while still giving the top end hit.
Four-strokes have advanced too. Older versions had big pistons in contrast to the slim ones sported by modern models. These pistons can move up to 12,000 rpm, which is a remarkable 200 times a second.
The response and flexibility of such an engine are naturally impressive. These engines deliver a linear power curve that was just a dream years ago. This seems to be the secret to the success of the four-stroke.
Because the power of the four-stroke is more user-friendly, it particularly shines in regions where traction is vital, giving it an advantage over the 2-stroke. A 4-stroke rider will be more eager to take their machine inside ruts and in hard packed dirt.
Its success can be traced to its engine cycle when generating power. A 4-stroke produces energy on every other stroke of its piston, making the power more manageable. Wheel spin is generally kept at a minimum.
Gear selection is less vital with the 4-strokes as the bike will pull any gear from any speed. Two-stroke riders will be shifting through gears while four-stroke pilots just twist and go.
Two Stroke vs Four Stroke for Enduro
Two-strokes have been making a steady comeback in all forms of riding, including Enduro. They are lighter, but they demand more work from the rider, making them harder to ride. Some riders argue that this increased interaction with the bike is what makes the sport fun.
A two-stroke forces the rider to learn the fundamentals of throttle control, braking, cornering, and choosing the right gear. At the end of an enduro session, therefore, the pilot on the two-stroke will be more exhausted than one on the four-stroke.
A four-stroke offers more power and torque so that the rider does not need to pick many strategic lines to overcome obstacles. The models produce a more predictable and smoother power delivery.
It is, therefore, easier to handle on the trails. The four-stroke is also more fuel-efficient, which is an advantage when riding in isolated areas that lack gas stations. Riders also do not have to remember to carry sufficient two-stroke oil with every trip.
Four-strokes shine is steep, slippery, and angles banks where a two-stroke would slide to the bottom. Four strokes also prefer the kind of perfect traction found in hard dirt. It will, however, struggle in mud, sand, and potholes.
Two-strokes are masters in big whoops and work quite well in loam. The deeper the sand on the ground, the faster the motorcycle will go because its light weight enables it to get on top. The models will not do well in hard dirt.
Which is Faster Two Stroke or Four Stroke?
Two-stroke engines will emerge as the fastest of the two models because they exhibit an intense kick to the motor. A two-stroke engine can also rev much quicker than a four-stroke engine of similar displacement.
How Do You Tell if an Engine is Two or Four Stroke?
Most 4-stroke engines on dirt bikes are similar to the ones in cars. Two-stroke engines are not so popular in cars. The basic components are the same in a 2-stroke engine and 4-stroke one and include crankshaft, pistons, exhaust ports, cylinder blocks and heads, and fuel inlets.
All internal combustion engines work in a similar fashion, where the pistons move upwards and downwards inside the cylinder block.
The movements of the piston are generated by the explosions of a fuel-air mix ignited by a spark. A spark plug that sits on the engine’s top provides the spark.
The crankshaft is turned by the movements of the piston. The rotary motion of the crankshaft is transmitted through the clutch and gearbox via the sprockets and chain to your dirt bike’s rear wheel.
The differences between the two engines are primarily mechanical. A two-stroke engine functions on two cycles of a piston. On one stroke, the fuel-air mix drains in the combustion chamber through the transfer pipe from the crankcase. As the piston comes close to the top part of the combustion chamber, the spark plug sparks the compressed fuel-air mix.
The combustion results in high pressure and forces the piston down on the other stroke. The air pressure in the crankcase is reduced during the first cycle, and this reduced pressure attracts more fuel and air mix, in readiness for the next cycle.
A four-stroke engine relies on two downward and two upward strokes. The strokes are termed as the intake, compressed, combustion, and exhaust strokes.
The fuel valves open to accommodate an air-fuel mix in the engine’s combustion chamber. During the compression stroke, the piston surges up in the cylinder barrel to compress the air-fuel mix.
The combustion stroke involves the ignition of the compressed fuel by the spark plug. This combustion results in high pressure in the cylinder chamber, which forces the piston down.
The exhaust stroke involves the opening of the exhaust valves to let out any exhaust generated from the combusted fuel.
A two-stroke engine basically consolidates the processes of a four-stroke model into two operations and is, therefore, more compact. Two-stroke engines will generally not have valves since intake and exhaust are included in the combustion and compression of the piston.
The engines also lack a chamber for the oil, which is why riders have to mix with fuel before riding. The specific ration will be guided by the manufacturer’s manual. A four-stroke engine accommodates a compartment for oil which makes work easier.
This is a simple way of telling the engines apart. Sound can also be relied upon as a distinction. Two-stroke engines characteristically have a loud, high-pitched sound, in comparison to the soft humming noise of the four-stroke engine.
What Happens if You Put 4 Stroke Fuel in a Two Stroke Engine?
A 4 stroke motor can run with a mixture made for a two-stroke engine. It will not damage the engine, but there will be smoke from the foul plugs and exhaust over time.
The debate concerning two-stroke and four-stroke engines is not about to come to an end. Dirt bike riders have taken firm stances on their preferred models. When it comes to weight, for example, four-strokes are heavier, and they plant themselves on the ground with more authority.
The two-stroke is, however, lighter and will be quicker at making quick flicks, changing directions, and bunny-hopping.
The four-stroke engine is, on the other hand, easier to use, and you will be less exhausted on trails. You get more power, torque, and tractability with the motors which makes the four-stroke dirt bikes a joy to ride on enduro.
Riding a two-stroke bike will bring back the nostalgia of the old days where dirt bike riding required work. You will have to work the grips and levers and increase your interaction with the bike.
Two-strokes are generally cheaper to buy, especially for used ones. Their parts are also cheaper, although you will have to maintain it more regularly than four-stroke models. It, however, comes down to preference.
Some riders gravitate to the ease of use presented by four-stroke engines in comparison to the much more control on the part of the pilot needed on the two-stroke motors.
Nice article Josh. I’ve owned both 2 and 4-stroke bikes over the years. I liken the 2-stroke sound as “ringy dingy” or “raspy” vs the softer “booming” or “thumping” note of the 4-stroke.
A 1974 Suzuki TS125 and a 1991 KTM250 EX/C were the only 2-strokes of mine. All the rest (all road bikes) were 4s.
Thanks again for a cool article.