Im probably not the best person for this, but oh well. This is something im doing for no reason at all and for anyone who might not know and/or care.
There are many advantages and disadvantages to each motor, they are both great and both do their job the way it should be done.
2 strokes:
2 strokes dominated the motorcross world in the 70s, 80s, and 90s. The early 2000s saw many 2 stroke races as well, but with the evolution of 4 strokes and new EPA regulations the 2 stroke started fading away in the motorcross circuit.
2 strokes are a simple motor with few moving parts allowing them to be more compact and lighter than a 4 stroke motor. This also makes them cheaper to rebuild when the time comes. Unlike a 4 stroke that has valves that work the intake and exhaust of the engine, the 2 stroke uses reeds, ports in the cylinder, and a large exhaust header pipe known as the expansion chamber to keep its pressure. The expansion chamber keeps the back pressure by "reflecting" some of the exhaust pulses back towards the engine, allowing the cylinder to hold more fuel for the next ignition. The power of the motor at certain RPMs is determined by the distance of the expansion chamber from the cylinder ports and its shape. The exhaust is useless if no fuel is burned in the cylinder to produce the exhaust so lets head inside the motor and see how it works. Unlike a 4 stroke the fuel does not go directly to the cylinder through the intake valves, a 2 stroke pulls its fuel through reed valves and into an intake port that goes directly to the crank (this is why oil is mixed to the gas!). The fuel is delivered to the crank on the pistons down, or power stroke, which creates a vacuum and negative pressure in the cylinder, the pressurized fuel in the crank follows a transfer port from the crankcase to the cylinder. On the compression stroke of the piston the transfer port is closed off causing another vacuum in the crank which opens the reed valve allowing more fuel into the crank, once the fuel is ignited by the spark plug the piston is forced down on its power stoke starting the process all over again. the two strokes are compression and power. This allows the 2 stroke to ignite the fuel on every stroke rather every other like the 4 stroke. Here is a link to all the BS I just said, http://www.animatedengines.com/twostroke.html.
And here is a video for those too lazy to read the link or what I just typed.
WARNING!!!
THIS VIDEO IS NOT HOW A 2 STROKE MOTOR WORKS! IT IS JUST HERE FOR SHITS AND GIGGLES!
One common myth of the 2 stroke is that it has twice the power of the same size 4 stroke. This is not true, in reality it has roughly 10 more horsepower than a same size 4 stroke. For example, a YZ250F (4 stroke) has 36 horsepower where as a YZ250 (2 stroke) has 47 (roughly the same as a YZ450F (4 stroke) which has 49 horsepower), These are stock numbers of the bike right off the factory line. Open up the bikes and these numbers will rise tremendously. This was probably started by someone who saw the numbers as fractions (i.e. 1/2 is twice the size of 1/4) so since the two stroke has half the strokes it must be twice as strong.
Advantages and Disadvantages of the two stroke.
Advantages:
High power to weight ratio
compact and lighter
cost less
fire every stroke giving a big power boost
Disadvantages:
Shorter life than a 4 stroke meaning more rebuilds
Pollute (this is caused by unburned fuel escaping out of the exhaust since there are no valves to hold it back)
Foul plugs quicker thanks to the oil in the fuel
more expensive to fill up since the oil has to be mixed in
4 strokes:
The 4 stroke dirt bike is nothing new, it has been around just as long as the 2 stroke but it never really took off until the early 2000s when they got a major overhaul and started appearing in the motorcross circuit. Before then they were mainly endure and adventure bikes for the trail rider. They were heavy and therefor slower and not as nimble as a 2 stroke. This was a turn off for the racers of the day meaning the 4 stroke didn't see much race action in the 80s and 90s. Thanks to EPA regulations and sound regulations the 4 stroke is now the main bike in the motorcross circuit.
Although a more complex motor, the modern day 4 stroke is a power house and a master of low end torque. Using valves for intake and exhaust it keeps more pressure in the cylinder allowing for better fuel burn. The 4 stroke also has a dedicated lubrication system unlike the 2 stroke which gives it a longer life, this means they require regular oil changes unlike the 2 stroke which does need the gear oil to be changed every now and then. The 4 stroke intake goes directly to the intake valves which open up allowing the fuel into the cylinder, this happens on the downward intake stroke of the piston. After the fuel is in the cylinder the compression stroke begins, when the fuel is ignited the piston is forced down, the intake valve does not open on this stroke. As the piston is returning to the top the exhaust valve opens allowing the burnt fuel to escape through the exhaust pipe, there is no ignition on this stroke. The momentum of the crank pulls the piston back down and the intake valve opens allowing fuel in and the process starts all over again. The 4 strokes are intake, compression, power, and exhaust. These strokes are controlled by a timing chain that is directly linked to the crank and to either a single or dual overhead cam system that works the opening and closing of the valves. The constant cylinder pressure means the 4 stroke can operate in lower RPMs which gives it a wider selection of power, unlike the 2 stroke which has to work at higher RPMs which gives it a narrow selection of power. Although the 4 stroke has a longer life and is more reliable it is more expensive to rebuild if needed. Although the 2 stroke is quicker, a 4 stroke is generally faster over a further distance. The 2 stroke revs out quickly making it snappy for the first few hundred yards or so but will not sustain this speed for long. The 4 stroke revs out slower meaning it can go for longer distances while maintaining its speed. Again here is a link to all the BS I just typed http://www.animatedengines.com/otto.html.
And a video for the lazy
Advantages and Disadvantages of the 4 stroke.
Advantages:
quieter than a 2 stroke
more reliable
good fuel usage meaning better fuel economy and less pollution
No need to mix gas
Disadvantages:
Heavier
expensive to repair when needed
less power in same CC as 2 stroke
more complex meaning more can go wrong
Both are great motors and will provide hours of fun. As long as you ride it doesn't matter what you ride so long as you have fun.
I personally like 4 strokes, the low end torque is perfect for woods riding. Im a big guy so I like the feel of a big bike.
Whatever you prefer it doesn't matter so long as there is fun involved.
Just something I typed up for the sake of because.
Thanks for reading
References:
http://www.smalloutboards.com/4Stroke.htm
http://www.animatedengines.com/otto.html
http://www.animatedengines.com/twostroke.html
There are many advantages and disadvantages to each motor, they are both great and both do their job the way it should be done.
2 strokes:
2 strokes dominated the motorcross world in the 70s, 80s, and 90s. The early 2000s saw many 2 stroke races as well, but with the evolution of 4 strokes and new EPA regulations the 2 stroke started fading away in the motorcross circuit.
2 strokes are a simple motor with few moving parts allowing them to be more compact and lighter than a 4 stroke motor. This also makes them cheaper to rebuild when the time comes. Unlike a 4 stroke that has valves that work the intake and exhaust of the engine, the 2 stroke uses reeds, ports in the cylinder, and a large exhaust header pipe known as the expansion chamber to keep its pressure. The expansion chamber keeps the back pressure by "reflecting" some of the exhaust pulses back towards the engine, allowing the cylinder to hold more fuel for the next ignition. The power of the motor at certain RPMs is determined by the distance of the expansion chamber from the cylinder ports and its shape. The exhaust is useless if no fuel is burned in the cylinder to produce the exhaust so lets head inside the motor and see how it works. Unlike a 4 stroke the fuel does not go directly to the cylinder through the intake valves, a 2 stroke pulls its fuel through reed valves and into an intake port that goes directly to the crank (this is why oil is mixed to the gas!). The fuel is delivered to the crank on the pistons down, or power stroke, which creates a vacuum and negative pressure in the cylinder, the pressurized fuel in the crank follows a transfer port from the crankcase to the cylinder. On the compression stroke of the piston the transfer port is closed off causing another vacuum in the crank which opens the reed valve allowing more fuel into the crank, once the fuel is ignited by the spark plug the piston is forced down on its power stoke starting the process all over again. the two strokes are compression and power. This allows the 2 stroke to ignite the fuel on every stroke rather every other like the 4 stroke. Here is a link to all the BS I just said, http://www.animatedengines.com/twostroke.html.
And here is a video for those too lazy to read the link or what I just typed.
WARNING!!!
THIS VIDEO IS NOT HOW A 2 STROKE MOTOR WORKS! IT IS JUST HERE FOR SHITS AND GIGGLES!
One common myth of the 2 stroke is that it has twice the power of the same size 4 stroke. This is not true, in reality it has roughly 10 more horsepower than a same size 4 stroke. For example, a YZ250F (4 stroke) has 36 horsepower where as a YZ250 (2 stroke) has 47 (roughly the same as a YZ450F (4 stroke) which has 49 horsepower), These are stock numbers of the bike right off the factory line. Open up the bikes and these numbers will rise tremendously. This was probably started by someone who saw the numbers as fractions (i.e. 1/2 is twice the size of 1/4) so since the two stroke has half the strokes it must be twice as strong.
Advantages and Disadvantages of the two stroke.
Advantages:
High power to weight ratio
compact and lighter
cost less
fire every stroke giving a big power boost
Disadvantages:
Shorter life than a 4 stroke meaning more rebuilds
Pollute (this is caused by unburned fuel escaping out of the exhaust since there are no valves to hold it back)
Foul plugs quicker thanks to the oil in the fuel
more expensive to fill up since the oil has to be mixed in
4 strokes:
The 4 stroke dirt bike is nothing new, it has been around just as long as the 2 stroke but it never really took off until the early 2000s when they got a major overhaul and started appearing in the motorcross circuit. Before then they were mainly endure and adventure bikes for the trail rider. They were heavy and therefor slower and not as nimble as a 2 stroke. This was a turn off for the racers of the day meaning the 4 stroke didn't see much race action in the 80s and 90s. Thanks to EPA regulations and sound regulations the 4 stroke is now the main bike in the motorcross circuit.
Although a more complex motor, the modern day 4 stroke is a power house and a master of low end torque. Using valves for intake and exhaust it keeps more pressure in the cylinder allowing for better fuel burn. The 4 stroke also has a dedicated lubrication system unlike the 2 stroke which gives it a longer life, this means they require regular oil changes unlike the 2 stroke which does need the gear oil to be changed every now and then. The 4 stroke intake goes directly to the intake valves which open up allowing the fuel into the cylinder, this happens on the downward intake stroke of the piston. After the fuel is in the cylinder the compression stroke begins, when the fuel is ignited the piston is forced down, the intake valve does not open on this stroke. As the piston is returning to the top the exhaust valve opens allowing the burnt fuel to escape through the exhaust pipe, there is no ignition on this stroke. The momentum of the crank pulls the piston back down and the intake valve opens allowing fuel in and the process starts all over again. The 4 strokes are intake, compression, power, and exhaust. These strokes are controlled by a timing chain that is directly linked to the crank and to either a single or dual overhead cam system that works the opening and closing of the valves. The constant cylinder pressure means the 4 stroke can operate in lower RPMs which gives it a wider selection of power, unlike the 2 stroke which has to work at higher RPMs which gives it a narrow selection of power. Although the 4 stroke has a longer life and is more reliable it is more expensive to rebuild if needed. Although the 2 stroke is quicker, a 4 stroke is generally faster over a further distance. The 2 stroke revs out quickly making it snappy for the first few hundred yards or so but will not sustain this speed for long. The 4 stroke revs out slower meaning it can go for longer distances while maintaining its speed. Again here is a link to all the BS I just typed http://www.animatedengines.com/otto.html.
And a video for the lazy
Advantages and Disadvantages of the 4 stroke.
Advantages:
quieter than a 2 stroke
more reliable
good fuel usage meaning better fuel economy and less pollution
No need to mix gas
Disadvantages:
Heavier
expensive to repair when needed
less power in same CC as 2 stroke
more complex meaning more can go wrong
Both are great motors and will provide hours of fun. As long as you ride it doesn't matter what you ride so long as you have fun.
I personally like 4 strokes, the low end torque is perfect for woods riding. Im a big guy so I like the feel of a big bike.
Whatever you prefer it doesn't matter so long as there is fun involved.
Just something I typed up for the sake of because.
Thanks for reading
References:
http://www.smalloutboards.com/4Stroke.htm
http://www.animatedengines.com/otto.html
http://www.animatedengines.com/twostroke.html
