Even More Engine Trivia

[GPracer2500]

Does a four stroke allow for more or less traction than a two stroke? In other words, is there anything about the fundamental design of a two stroke vs. a four stroke that gives one a traction advantage?

Many of us with experience in both types of engines might say that two strokes are more likely to spin the tires (i.e. less traction). But two strokes frequently have comparitively narrower powerbands and a "hit" that comes on suddenly.

Sooooo, to make the comparision fair lets assume that the two ATV's we're comparing have identical dimensions/weights (wheelbase, weight distribution, etc), identical tires, identical power numbers (i.e. if you dyno'd them their respective graphs would lay right ontop of each other), and identical everything else. The only difference is that one does it with four strokes and the other does it with two.

For bonus points ;) explain your answer.



If you're not sure, just guess! This is just for fun, after all.

[wilkin250r]

I'm interested in the replies.

[Aceman]

If everything is the same including the dyno graphs, I'd have to say traction would also be the same. But it's probably a trick question? :cuss: :D Hell, maybe it's the same even if the dyno graphs were different. Aaaghh, damn you GP and your brain teasers!:blah:

[zrpilot]

The only difference (assuming identical dynos plots, weights including rider, and available traction) that I see is the amount of rotating mass. A four stroker would have more rotating mass that would make it store more kinetic energy and therefore possibly spin more...

But just a stab in the unknown

[1fst400]

To me every time I ride a 2 smoke, its boggy then all of a soden your spinnning and swerving out of control.

so my vote is 2 stroke spins more

[underpowered]

i wouls say the 4-poke would have more traction just due to the typical power delivery of it. the 4 stroke usually ha s more linear pull, not the sudden snap of the 2-smokes power band. i would say due to how the power is delivered a 4 stroke would have more traction

[banshee84]

well in your explanation of the question you said the dyno charts would be the same if you lay one on top of the other and the bike dimensions are the same so the traction would be the same. In the real world though four strokes do get a lot more traction though because of the power delivery. I ride a banshee and it doesn;t get much traction in the dirt due to all the top end and no bottom end. but a utility quad gets tons of traction in the dirt

[400exstud]

I would say that the two stroke will have more traction

I say this because if both engines are making the same amount of power at the same RPM (ie identicle dynos), the two stroke will fire twice as many times as the four stroke. The extra fire would smooth out the power delivery and make it less choppy; whereas, the four banger would fire..........wait and fire again.

Eh, what can I say. I tried my best.

[Old Head]

4 stroke has more traction because the power comes on smoother. when the 2 stroke hits the power band it lets loose.

[GPracer2500]

Remember, the two engines we're comparing have identical looking dyno graphs--the same torque/HP outputs at the same RPMs, the same "powerbands".

We all know that a sudden, viloent "powerband" is good at breaking tires loose. So that factor is being removed from this two vs. four stroke comparison.



BTW, hint #1: 400exstud's line of thinking is very close to the root issue I'm trying to get at [thumbsup!].

[400exrider707]

Well if they have the exact same power output at the exact same RPMS and look identical on the dyno, I would say that traction would be the same. The chain and sprockets which are turning the tires, dont see differnt outputs, the have one output of power turning the same set of tires, there should be no difference, IF they are the exact same power characteristics. Eh its a shot in the dark but at least its a shot.:D

[chuckys400ex]

in my own expirance a 4-stroke provides more traction.i have very bald tires on the back of my 400ex and i can stop in the middle of a mild muddy hillclimb and then take back off with out spinning the tires at all,but my buddies banshee with brand new itp holeshots will try the thing and would have to back all the way down the hill and try again becuse all he does is spin .so long story short i would say the thumpers have the avantage

[moto04racing]

the third option... but yet they could all be right.. depending on conditions, tires, engine power, rider weight and machine weight.

[300exOH]

When you say the 2 engines are the same when graphed on a dyno sheet are you talking horsepower or torque? Personally I would say the 4 stroke would get better traction because of its low end torque. Even if the HP ratings were the same you will never get the torque out of a 2-stroke you can get out of the 4-stroke... Torque is what gets things moving so my vote is for the 4 stroke.

Interesting topic though.;)

edit: I forgot to add that a 4-stroke has more internal moving parts than a 2-stroke and therefore more rotating mass, which equals more torque and more traction.:D

[400exrider707]

Originally posted by GPracer2500
Remember, the two engines we're comparing have identical looking dyno graphs--the same torque/HP outputs at the same RPMs, the same "powerbands".

We all know that a sudden, viloent "powerband" is good at breaking tires loose. So that factor is being removed from this two vs. four stroke comparison.



BTW, hint: 400exstud's line of thinking is very close to the root issue I'm trying to get at [thumbsup!].

Im quoting this in hopes that maybe some people will read before they post their thoughts. PLEASE READ THIS POST FIRST!!!:rolleyes:

[GPracer2500]

Yep. The two hypothetical engines in this comparison measure the same torque and HP output at the same RPMs as measured on a dyno. The only difference between them is that one occomplishes this with four strokes and the other does it with two.

I should also add they are both single cylinder engines (or both twins, or both tripples, etc). That's hint #2--if you can figure out why that would matter then you've pretty much figured this out.

Here's hint #3: Think about what is happening at the contact patch of the tires when an engine is laying down its power. Is the exact same thing happening for a two stroke and a four stroke? Is there an element of time involved?

[sideways]

ive owned both 2 and 4 stroke quads. had a 98 banshee and now have a 00 416ex. the ex gets better traction than the banshee did. thats real life experience.
now on to this imaginery world where a 2stroke and a 4 stroke are perfectly matched in power and torque with the same powerband. i believe this to be a trick question. a 4 stroke puts out a different type of power than a 2 stroke. 2 stroke doesnt have low end torque, a 4 stroke does. a 2 stroke has a higher revving engine than a 4 stroke, therefore produces its power at a higher rpm.
i believe from a dead stop, the 4 stroke would grip better because of its low end power.

i tried, but prolly failled

[400exstud]

Originally posted by GPracer2500
Yep. The two hypothetical engines in this comparison measure the same torque and HP output at the same RPMs as measured on a dyno. The only difference between them is that one occomplishes this with four strokes and the other does it with two.

I should also add they are both single cylinder engines (or both twins, or both tripples, etc). That's hint #2--if you can figure out why that would matter then you've pretty much figured this out.

Here's hint #3: Think about what is happening at the contact patch of the tires when an engine is laying down its power. Is the exact same thing happening for a two stroke and a four stroke? Is there an element of time involved?

#3 was what I was initially getting at. There is roughly 2X the elapsed time before ignition with a 4-stroke versus a two stroke. This would mean that for at the same RPM, the 4-stroke would have to have one heck of a powerstroke to equal the strokes of the two stroke. This single stroke, combined with the increased elapsed time would cause the 4-stroke to have LESS traction than the 2-stroke.

[GPracer2500]

You've almost got it, 400exstud. You're definitely on the right track, just misinterpreting the precise influence of the forces involved.



Answer: In my hypothetical comparison, the four stroke would have more traction.

Short explination: The reason centers around the power pulses created by each engine. The farther apart the power pulses are the more time the tires have to recover and regain grip. The two stroke's power pulses come once every 360 degrees while the four stroke's come every 720 degrees (that's degrees of crank rotation). That gives the four stroke's tires a much longer time between power pulses to stop slipping and start gripping again. If a slipping tire doesn't have time to stop slipping before the next power pulse arrives, it will spin-up and you've lost most of your traction.


Longer explination:
A lot of times we'll think of engines as delivering a nice even stream of power. But they don't. They deliver power in a rapid succession of "power pulses". Each time the a/f mixture gets burned on the power stroke a pulse of power is sent through the drivetrain and on to the contact patch of each wheel.

With a single cylinder two stroke, a power pulse is generated every 360 degrees of crank rotation--one pulse for each rotation of the crank. A four stroke produces a power pulse half as often--every 720 degrees of crank rotation.

If we were to look at an ATV tire vigorously accelerating in slow motion we'd find that every time the contact patch is subjected to a power pulse the tire slips just a little bit. As soon as the power pulse ends the tire recovers from this slip and grips the surface until the next power pulse arrives.

During these slip and grip phases there are two different types of friction being utilized. Static friction is the friction between two sufaces that are not sliding against each other. This is the friction in play between power pulses. Kinetic friction is the friction between two surfaces that are sliding agains each other. This is the friction that's occuring (to a greater or lesser degree) during each power stroke. Static friction is nearly always the more powerful of the two. [note: there's another way in which traction is obtained (interference traction) but for simplicity I'm leaving that out of the conversation. Interference traction can be neatly bundled into static friction.] The differences in these two types of friction explains why a wheel that's at the maximum braking level without locking up and sliding will stop sooner than one that is locked up and sliding. To get maximum traction we want the tires to spend as much time as possible NOT sliding.

If enough power is applied the tires may break traction completely and start to spin-up. What happens is that the low traction kenetic friction present during the powerstroke spills over beyond the powerstoke period into the period of time when the tires would othewise be recovering. With a two stroke you've only got about 180 degrees of wiggle room before the next power pulse arrives. A four stroke has 540 degrees with which to absorb any spillover. If the tires don't have a chance to revover between power pulses the tires spin-up.

Single cylinder four strokes enjoy some of the greatest potential traction of any engine design. Part of why Banshees have such a notorious reputation for spinning up their tires is because they are twin cylinder two strokes. Banshees send 4 power pulse to the tires for every 1 sent by a 400EX. That means that at the same RPM, the 400EX's tires have 4 times as much time to recover and regain traction since the last power pulse.

All of this helps explain WHY low rpm torque is so good for traction. Get on the gas from low rpm on a Raptor or even a 400EX and you can feel the tires clawing at the ground and accelerating you away. Aside from the spacing of power pulses relative to crank rotation, low rpm spreads them out too. Since four strokes are generally better at producing low rpm power, that's just icing of the cake for 4 bangers.

The spacing of power pulses has been a big factor in MotoGP motorcycle racing. Both Honda, Yamaha, and Ducati have used engines with very specific crank phasing designed to manipulate the deliverly of power pulses. Honda had a 500cc 2 stroke V-4 that fired all four cylinders within 70 degrees of one another instead of the traditional way of firing each cylinder 90 degrees apart. It was called the "Big-Bang" engine because all the cylinders nearly fired at the same time. It hurt power and increased vibration but allowed for faster lap times. Riders could accelerate out of corners earlier and with more control because the "Big-Bang" crank phasing gave the tire more traction.

Most multi-cylinder motorcycles/ATVs/snowmobiles/etc use even crank phasing (sometimes called firing order--but it's really crank phasing not firing order). But a special few go against the grain to reap the benefits of widely spaced power pulses. The Honda RC30 and RC45 and the BMW F800ST come to mind. Harely Davidson engines use a shared crank pin for each connecting rod. They fire every at 315 degrees, then 405 degrees, then 315, then 405, etc, etc. instead of firing evenly every 360 degrees. This is a big part of what gives HDs their unique sound. The difference here is HD started doing this ages ago for manufacturing simplicity (not performance) and it's become such a big part HD's character that it stuck.

But back to traction--the farther apart you can space your power pulses (by way of RPM, number of cylinders, crank phasing, or number of strokes) the more potential traction the engine will have.


Thanks for all that participated!! :cool:

[5,15,16]

[400exstud]

I agree 100% with the elapsed time helps to gain traction thinking; however, I still have 1 small problem.

If at any given RPM, the 2 stroke and 4 stroke engines have equal power the 4 stroke will have to have more umph in its 1 power stroke verses the 2 that occur during the some 2 revolutions. Is my thinking off? I was just thinking that if they have the same amount of power at each stroke and the 2 stroke has twice as many strokes it would have an overall of more power. If I am thinking right, the 4 stroke would spin the tires sooner because of the intensity of its stroke in relation to that of the 2 stroke.

Sorry. That was rough, but I can't seem to get it any better.

By the way GPracer2500, how did you get so knowledgeable about this stuff? I really like chatting about this theoretical and technical stuff. It seems that with the majority of people, as soon as you start up a conversation like this everyone looks at you like you are a freak. At least I am not the only freak that enjoys this stuff.

[sideways]

Originally posted by GPracer2500
You've almost got it, 400exstud. You're definitely on the right track, just misinterpreting the precise influence of the forces involved.



Answer: In my hypothetical comparison, the four stroke would have more traction.

Short explination: The reason centers around the power pulses created by each engine. The farther apart the power pulses are the more time the tires have to recover and regain grip. The two stroke's power pulses come once every 360 degrees while the four stroke's come every 720 degrees. That gives the four stroke's tires a much longer time between power pulses to stop slipping and start gripping again. If a slipping tire doesn't have time to stop slipping before the next power pulse arrives, it will spin-up and you've lost most of your traction.


Longer explination:
A lot of times we'll think of engines as delivering a nice even stream of power. But they don't. They deliver power in a rapid succession of "power pulses". Each time the a/f mixture gets burned on the power stroke a pulse of power is sent through the drivetrain and on to the contact patch of each wheel.

With a single cylinder two stroke, a power pulse is generated every 360 degrees of crank rotation--one pulse for each rotation of the crank. A four stroke produces a power pulse half as often--every 720 degrees of crank rotation.

If we were to look at an ATV tire vigorously accelerating in slow motion we'd find that every time the contact patch is subjected to a power pulse the tire slips just a little bit. As soon as the power pulse ends the tire recovers from this slip and grips the surface until the next power pulse arrives.

During these slip and grip phases there are two different types of friction being utilized. Static friction is the friction between two sufaces that are not sliding against each other. This is the friction in play between power pulses. Kinetic friction is the friction between two surfaces that are sliding agains each other. This is the friction that's occuring (to a greater or lesser degree) during each power stroke. Static friction is nearly always the more powerful of the two. [note: there's another way in which traction is obtained (interference traction) but for simplicity I'm leaving that out of the conversation. Interference traction can be neatly bundled into static friction.] The differences in these two types of friction explains why a wheel that's at the maximum braking level without locking up and sliding will stop sooner than one that is locked up and sliding. To get maximum traction we want the tires to spend as much time as possible NOT sliding.

If enough power is applied the tires may break traction completely and start to spin-up. What happens is that the low traction kenetic friction present during the powerstroke spills over beyond the powerstoke period into the period of time when the tires would othewise be recovering. With a two stroke you've only got about 180 degrees of wiggle room before the next power pulse arrives. A four stroke has 540 degrees with which to absorb any spillover. If the tires don't have a chance to revover between power pulses the tires spin-up.

Single cylinder four strokes enjoy some of the greatest potential traction of any engine design. Part of why Banshees have such a notorious reputation for spinning up their tires is because they are twin cylinder two strokes. Banshees send 4 power pulse to the tires for every 1 sent by a 400EX. That means that at the same RPM, the 400EX's tires have 4 times as much time to recover and regain traction since the last power pulse.

All of this helps explain WHY low rpm torque is so good for traction. Get on the gas from low rpm on a Raptor or even a 400EX and you can feel the tires clawing at the ground and accelerating you away. Aside from the spacing of power pulses relative to crank rotation, low rpm spreads them out too. Since four strokes are generally better at producing low rpm power, that's just icing of the cake for 4 bangers.

The spacing of power pulses has been a big factor in MotoGP motorcycle racing. Both Honda, Yamaha, and Ducati have used engines with very specific crank phasing designed to manipulate the deliverly of power pulses. Honda had a 500cc 2 stroke V-4 that fired all four cylinders within 70 degrees of one another instead of the traditional way of firing each cylinder 90 degrees apart. It was called the "Big-Bang" engine because all the cylinders nearly fired at the same time. It hurt power and increased vibration but allowed for faster lap times. Riders could accelerate out of corners earlier and with more control because the "Big-Bang" crank phasing gave the tire more traction.

Most multi-cylinder motorcycles/ATVs/snowmobiles/etc use even crank phasing (sometimes called firing order--but it's really crank phasing not firing order). But a special few go against the grain to reap the benefits of widely spaced power pulses. The Honda RC30 and RC45 and the BMW F800ST come to mind. Harely Davidson engines use a shared crank pin for each connecting rod. They fire every at 315 degrees, then 405 degrees, then 315, then 405, etc, etc. instead of firing evenly every 360 degrees. This is a big part of what gives HDs their unique sound. The difference here is HD started doing this ages ago for manufacturing simplicity (not performance) and it's become such a big part HD's character that it stuck.

But back to traction--the farther apart you can space your power pulses (by way of RPM, number of cylinders, crank phasing, or number of strokes) the more potential traction the engine will have.


Thanks for all that participated!! :cool:

[5,15,16]








:confused: :confused: :eek2: :ermm: :confused: :eek2: :confused:

this may take a while to comprehend, but somehow it makes sense

[GPracer2500]

400exstud: With these two engines, the four stroke power pulses would be more powerful since there are half as many of them yet the total output is the same. But that fact doesn't outweigh the difference in time for the tires to regain traction between pulses.

Lets assume both the four stroke and two stroke power pulses last 180 degrees of crank rotation. The two stroke will only have 180 degrees of "non-power pulse" crank rotation before we're back at another power pulse. The four stroke will have 540 degrees of "non-power pulse" crank rotation before the next power pulse. 180 vs. 540. That's a lot more time (3 times as much) for the four stroke. Even if it worked out to a 1:1 relationship between power pulse strength and time needed (after the power pulse ends) to regain traction, a four stroke with twice the power in each pulse would still have enough time to grip before the next pulse.

See what I'm saying? The four stroke pulse would have to be strong enough to spin the tire for a full 540 degrees of crank rotation after the power pulse in order to spin-up the tires. The two stroke only has to spin the tires for 180 degrees of crank rotation before a spin-up will occur. Even though each two stoke pulse is half as strong, it's got three times less time to start gripping again.

[wilkin250r]

Yeah, but that's the way these things work, isn't isn't it?

Ok, so the 4 stroke has more time between power pulses. But they are twice as strong, (and theoretically last longer. With the exhaust port opening, a 2-stroke has only about 90 degrees of power, while the 4-stroke can just shy of 180 degrees).

Throw a ball twice as high, it doesn't stay up twice as long. In reality, 4ft high stays up only about 1.5 times as long as 2ft high. If you want twice the time of 2ft high, you need 8ft high.

So twice as strong a power surge, and 4 times as long between pulses sounds about right to me.









I say identical traction. But what do I know. ;)

[400exrider707]

Although the argument makes sense to me, it seems like that the difference is so small it is almost negligible. A good set of tires would make more of a difference than power pulses IMO.

[Chino886]

How much time are we experiencing in between pulses?

I understand the "power" pulse theory, but I am question whether there would be significant time to create a difference in traction.............given the same powerband. My thinking is since the powerband is the same, the harmonics of the "pulses" are identical.

Just my unedjumacated opinion!

:devil:

[54warrior]

Originally posted by Chino886
How much time are we experiencing in between pulses?


2 Stroke:

At 8000 RPM it would be approximately 133.333 pulses per second!!!

8000Rev/min * 1min/60sec * = 133.33 RPS

133 Rev/sec * 360deg/1 rev * 1 pulse/ 360 deg = 133.33 Pulses/sec

Thats ONE pulse every 0.0075 seconds.


Please correct my math if I'm incorrect.

[Chino886]

Originally posted by 54warrior
2 Stroke:

At 8000 RPM it would be approximately 133.333 pulses per second!!!

8000Rev/min * 1min/60sec * = 133.33 RPS

133 Rev/sec * 360deg/1 rev * 1 pulse/ 360 deg = 133.33 Pulses/sec

Thats ONE pulse every 0.0075 seconds.


Please correct my math if I'm incorrect.

So, with that math, If I come into a corner hot, slam the rear brakes and slide my arse around the corner, the extra traction would be unnoticed for me on the MX track...........with the hypothetical example...........

Just having fun guys!

[400exrider707]

Originally posted by 54warrior
2 Stroke:

At 8000 RPM it would be approximately 133.333 pulses per second!!!

8000Rev/min * 1min/60sec * = 133.33 RPS

133 Rev/sec * 360deg/1 rev * 1 pulse/ 360 deg = 133.33 Pulses/sec

Thats ONE pulse every 0.0075 seconds.


Please correct my math if I'm incorrect.

One of those revolutions is exhaust, so there is no power pulse. So you would have 66.6666666 power pulses per second

[underpowered]

Originally posted by 400exrider707
One of those revolutions is exhaust, so there is no power pulse. So you would have 66.6666666 power pulses per second

no, 1 stroke is only 180* of revolution, so 2 strokes is only 1 complete revolution of the crank. 4 strokes is only 2 complete revolutions. 1 stroke is a movement either up or down of the piston in the cylinder, not a revolution

[54warrior]

Originally posted by 400exrider707
One of those revolutions is exhaust, so there is no power pulse. So you would have 66.6666666 power pulses per second

I'm not sure I agree with what you are saying:

2 stroke engine: 2 strokes per one revolution of the crank. Intake/power stroke, and the exhaust stroke.

That means that there is ONE power stroke per one revolution.

One revolution equals 360 degrees.

If you look closely at my math, I used 1 pulse/360 degrees, which I feel is the correct method. What you are suggesting, is incorrect.

[400exrider707]

Originally posted by 54warrior
I'm not sure I agree with what you are saying:

2 stroke engine: 2 strokes per one revolution of the crank. Intake/power stroke, and the exhaust stroke.

That means that there is ONE power stroke per one revolution.

One revolution equals 360 degrees.

If you look closely at my math, I used 1 pulse/360 degrees, which I feel is the correct method. What you are suggesting, is incorrect.



Your 8000 RPMS, there would only be 4000 power pulses would there not?

[54warrior]

Originally posted by 400exrider707
Your 8000 RPMS, there would only be 4000 power pulses would there not?

Incorrect. That is all factored out into my math though when I use: 1 pulse/360deg

8000Rev/min = 133.33 Revs/second

133 Revs/sec * 360deg/1 rev * 1 pulse/ 360 deg = 133.33 Pulses/sec


4000 power pulses/minute * 1min/60sec =
66.66 pulses/second

^^^that is incorect though

8000rev/min does not equal 4000 power pulses per minute:

8000 rev/min * 1 power pulse/rev= 8000pulses/min

8000 pulses/min * 1min/60 sec = 133.33 pulses/second


It is important to cancel out all your units or it won't add up.


Basically one revolution would provide ONE power pulse. If each revolution is making ONE power pulse and it makes 8000 revolutions, it would make 8000 power pulses per minute.

I can easily see where you are getting confused because you certainly had me second guessing myself.

[400exrider707]

Originally posted by 54warrior
Incorrect. That is all factored out into my math though when I use: 1 pulse/360deg

8000Rev/min = 133.33 Revs/second

133 Revs/sec * 360deg/1 rev * 1 pulse/ 360 deg = 133.33 Pulses/sec


4000 power pulses/minute * 1min/60sec =
66.66 pulses/second

^^^that is incorect though

8000rev/min does not equal 4000 power pulses per minute:

8000 rev/min * 1 power pulse/rev= 8000pulses/min

8000 pulses/min * 1min/60 sec = 133.33 pulses/second


It is important to cancel out all your units or it won't add up.


Basically one revolution would provide ONE power pulse. If each revolution is making ONE power pulse and it makes 8000 revolutions, it would make 8000 power pulses per minute.

I can easily see where you are getting confused because you certainly had me second guessing myself.

There isn't a power pulse every revolution. There are two revolutions per cycle, only one has a power pulse. I'm not following something here.

[54warrior]

Originally posted by 400exrider707
There isn't a power pulse every revolution. There are two revolutions per cycle, only one has a power pulse. I'm not following something here.

I think you might have mis-read my original post when I stated: FOR A 2-STROKE ENGINE


On a 2-stroke engine, yes, there is a power pulse during each revolution.

On a 4-stroke engine, it is just as you describe, one power pulse per 2 revolutions


Two-stroke cycle engines operate in two strokes:

1. Power/exhaust: This stroke occurs immediately after the ignition of the charge. The piston is forced down. After a certain point, the top of the piston passes the exhaust port, and most of the pressurized exhaust gases escape. As the piston continues down, it compresses the air/fuel/oil mixture in the crankcase. Once the top of the piston passes the transfer port, the compressed charge enters the cylinder from the crankcase and any remaining exhaust is forced out.
2. Compression/intake: The air/fuel/oil mixture has entered the cylinder, and the piston begins to move up. This compresses the charge in the cylinder and draws a vacuum in the crankcase, pulling in more air, fuel, and oil from the carburetor. The compressed charge is ignited by the spark plug, and the cycle begins again.


Here are a couple good links that explain the difference between the two. Animations even:

Four Stroke Engines Explained (http://www.keveney.com/otto.html)
Two Stroke Engines Explained (http://www.keveney.com/twostroke.html)

[54warrior]

Also, the terminology "2-cycle" and "4-cycle" are confusing. Stroke is more appropriate.

When you think of cycle, you think something that is "complete" or one 360 degree revolution. That is not the case here. One cycle is really 180* of crankshaft rotation. Therefore, 2 cycles would be 360 degrees.

2 Stroke engine, 2 strokes: down stroke of the piston in the cylinder and upstroke of the piston

4 stroke engine, 4 strokes: down stroke (intake), upstroke (compression), down stroke (power), upstroke (exhaust)

[400exrider707]

Originally posted by 54warrior
Also, the terminology "2-cycle" and "4-cycle" are confusing. Stroke is more appropriate.

When you think of cycle, you think something that is "complete" or one 360 degree revolution. That is not the case here. One cycle is really 180* of crankshaft rotation. Therefore, 2 cycles would be 360 degrees.

2 Stroke engine, 2 strokes: down stroke of the piston in the cylinder and upstroke of the piston

4 stroke engine, 4 strokes: down stroke (intake), upstroke (compression), down stroke (power), upstroke (exhaust)

hahaha yeah sorry for the confusion. I understand the differences between the two engine, but thanks for the links hahaha, brain fart!:rolleyes: :p

[54warrior]

Originally posted by 400exrider707
hahaha yeah sorry for the confusion. I understand the differences between the two engine, but thanks for the links hahaha, brain fart!:rolleyes: :p


I've seen your posts before and knew you are pretty knowledgeable about things, I figured it was just a brain fart. happens to all of us

[parkers30]

If you have ever seen the tires on a Top fuel car during a launch you should be part of the way to understanding what GP is trying to explain. In a sense the tire/ground interface is acting as a damper.

Do you feel more in control going down a washboarded road in your car or over a speed bump?

[400exrider707]

Originally posted by parkers30
If you have ever seen the tires on a Top fuel car during a launch you should be part of the way to understanding what GP is trying to explain. In a sense the tire/ground interface is acting as a damper.

Do you feel more in control going down a washboarded road in your car or over a speed bump?

That doesn't really apply to the question at hand. We were looking strictly at engine differences. Anything past the countershaft sprocket wouldn't apply here.

[parkers30]

Originally posted by 400exrider707
That doesn't really apply to the question at hand. We were looking strictly at engine differences. Anything past the countershaft sprocket wouldn't apply here.

I think you missed my point.

He was asking about the traction it provides. While I do understand what he was asking fully. I was trying to make a little bit of analogy; something to show how the tire reacts to the power pulse in a more magnified way. I know that the tires deflecting on a topfuel car are more from one pulse, but they are reacting from a sudden 'hit' as the car launches trying to maintain traction as the weight of the car starts to move. If this pulse is too sudden or happens again too quickly, the tire slips. This happens because it does not have enough time to recover from the absorption of the original pulse. Pretty close to what he is trying to explian and something I am sure many of us have noticed when looking at pictures.

The washboard road analyogy was trying to translate it into something we all have most likely experienced first hand and have sensed the lack of control when going over a washboard road too fast. The fact that the suspension cannot react fast enough is part of the dynamics and design of the suspension. If it were able to react quickly enough to the washboard, in another case it would likely cause buck as it overshoots and recovers back towards the origin or setpoint. Its all about the damping ratio.

[400exrider707]

Originally posted by parkers30
I think you missed my point.

He was asking about the traction it provides. While I do understand what he was asking fully. I was trying to make a little bit of analogy. Something to show how the tire reacts to the power pulse in a more magnified way. I know that the tires deflecting on a topfuel car are more from one pulse, but they are reacting from a sudden 'hit' as the car launches trying to maintain traction as the weight of the car starts to move. If this pulse is too sudden or happens again too quickly the tire slips, as it does have enough time to recover from the absorption of the original pulse. Pretty close to what he is trying to explian and something I am sure many of us have noticed when looking at pictures.

The washboard road analyogy was trying to translate it into something we all have most likely experianced first hand and have sensed the lack of control when going over a washboard road too fast. The fact that the suspension cannot react fast enough is part of the dynamics and design of the suspension. If it were able to react quickly enough to the washboard, in another case it would likely cause buck as it overshoots and recovers back towards the origin or setpoint. Its all about the damping ratio.

understood... good info

[parkers30]

Just sharing the analogies I use as I try to understand complex subjects. Often times they help tremendously, especially when talking about thing that are somewhat foriegn to people, like the cumbustion cycle of a 4 cycle vs 2 cycle engine. How many people can look at a given graphed combustion cycle and determine the engine type and cycle? I know I would struggle the first time or two.

[pro-rider46]

if they are the same hp torque etc. at all rpms they should be exactly the same just one has two strokes (which wont show any difference from the four)and the other is a four stroke. they wont be any different from each other because they have the same hp ratings. therefore it is pretty much making a two stroke in to a four stroke.

i hope no one posted this before because i skipped to the last page.