Timming advance questions.

[jlsparky7]

What exactly does advancing the timming involve and what does it accually do? Considering doing it this winter when i get pipes, reeds, and shave the head.

Edited September 9, 2006 by jlsparky7

[BigRed350x]

What exactly does advancing the timming involve and what does it accually do? Considering doing it this winter when i get pipes, reeds, and shave the head.

 

do a quick search bud, this was covered a couple times just this past month.

 

It involves advancing the spark or retarding the spark to the cylinders TDC. Advancing it gives you more bottom end, retarding it gives more top. That's the long and short of it.

[Ducman]

You will need to pull the flywheel and replace the stock timing plate with an aftermarket adjustable one.

[Bansh-eman]

You will need to pull the flywheel and replace the stock timing plate with an aftermarket adjustable one.

 

not entirley true.... if your a handy man with machines you can make your stock plate adjustable. all it is , is the mounting hols have been longated and the degree marks put on the plate for ez use

[Polish]

 

not entirley true.... if your a handy man with machines you can make your stock plate adjustable. all it is , is the mounting hols have been longated and the degree marks put on the plate for ez use

 

 

 

thats Geto.........where you from the south? :yelrotflmao:

[greencoloredride]

do a quick search bud, this was covered a couple times just this past month.

 

It involves advancing the spark or retarding the spark to the cylinders TDC. Advancing it gives you more bottom end, retarding it gives more top. That's the long and short of it.

 

Is this true for 2strokes? Its completely wrong for cars. I dont see how retarding the timing would give more power to the topend of the power band. The reason timing advances(as in electronic or vacuum advances) in 4strokes is to keep up with the revolutions of the motor. When the motor revs faster, you have to ignite fuel sooner because it burns at a constant rate and if the timing is too retarded the you still have fuel burning long into the downstroke where its no longer making power in that cylinder. You want to advance the timing as much as possible without causing detonation or in exreteme advancing actually backfiring. Someone that is absolutely sure about this concerning 2strokes plz elaborate for me. I prefer to get the facts and Im still fairly new to 2 strokes but plan on becoming very knowledgable in them.

Edited September 10, 2006 by greencoloredride

[greencoloredride]

On the other hand, if u were talking about cams in a 4 stroke, youd be exactly right.

[BigRed350x]

Yes, it will give more top end (to a point) by retarding your timing. If you want more bottom end run it as high as possible. More bottom end, don't run it as high. Pretty simple. More top end run it stock or -2 more bottom end run it up around +4 to +7. I run mine between +7 and +9 most of the time.

[greencoloredride]

Yes, it will give more top end (to a point) by retarding your timing. If you want more bottom end run it as high as possible. More bottom end, don't run it as high. Pretty simple. More top end run it stock or -2 more bottom end run it up around +4 to +7. I run mine between +7 and +9 most of the time.

 

 

Can anyone technically explain to me as to why this is?

[canyncarvr]

Re: 'Can anyone technically explain to me as to why this is?'

 

This is quite an old post..but a straightforward question that for whatever reason wasn't answered.

 

The comment was made, '..not like four strokes...'

 

Yep. Pretty much backwards timing-wise.

 

The reason a two-stroke 'likes' retarded timing for upper-band RPM operation is due to the expansion chamber effect. A pipe on a 2-stroke performs two essential functions to 2-stroke performance. A 2-stroke pipe is composed of two cones, the first divergent, the next convergent. The pipe 'pulls' the incoming charge through the motor. That's the scavenging part. That's what the divergent cone accomplishes. The convergent cone acts..as you could guess...in an opposite fashion. It PUSHES the charge back into the cylinder before the piston closes the exhaust port. That's the supercharging effect.

 

The design of a particular expansion chamber..the size and length of the headpipe, the diameter and length of the cones (the bell part of an expansion chamber) all fit together to make a 2-stroke perform as is desired and WHERE (RPM-wise) it's desired. The expansion chamber tunes the pressure waves coming from the cyclic nature of the 2-stroke engine operation (opening/closing of the ports).

 

Retarding the timing on a 2-stroke motor transfers heat to the pipe..and it's that heat that tends to improve the scavenging/supercharging effect in the upper-RPM ranges.

 

Thats's why you see ignition timing being quite severely retarded as a general rule in most 2-stroke ignition controls.

 

And that is why 'this is'.

 

Cheers!

Edited December 28, 2006 by canyncarvr

[David Keith]

Re: 'Can anyone technically explain to me as to why this is?'

 

This is quite an old post..but a straightforward question that for whatever reason wasn't answered.

 

The comment was made, '..not like four strokes...'

 

Yep. Pretty much backwards timing-wise.

 

The reason a two-stroke 'likes' retarded timing for upper-band RPM operation is due to the expansion chamber effect. A pipe on a 2-stroke performs two essential functions to 2-stroke performance. A 2-stroke pipe is composed of two cones, the first divergent, the next convergent. The pipe 'pulls' the incoming charge through the motor. That's the scavenging part. That's what the divergent cone accomplishes. The convergent cone acts..as you could guess...in an opposite fashion. It PUSHES the charge back into the cylinder before the piston closes the exhaust port. That's the supercharging effect.

 

The design of a particular expansion chamber..the size and length of the headpipe, the diameter and length of the cones (the bell part of an expansion chamber) all fit together to make a 2-stroke perform as is desired and WHERE (RPM-wise) it's desired. The expansion chamber tunes the pressure waves coming from the cyclic nature of the 2-stroke engine operation (opening/closing of the ports).

 

Retarding the timing on a 2-stroke motor transfers heat to the pipe..and it's that heat that tends to improve the scavenging/supercharging effect in the upper-RPM ranges.

 

Thats's why you see ignition timing being quite severely retarded as a general rule in most 2-stroke ignition controls.

 

And that is why 'this is'.

 

Cheers!

That is a very good explanation. Why do most Banshee riders prefer +4 degrees? If it fires earlier than recommended, what is the real benefit?

[Bansh-eman]

That is a very good explanation. Why do most Banshee riders prefer +4 degrees? If it fires earlier than recommended, what is the real benefit?

banshees are notroiouse for not having bottom end... so they advance it to get that bottom end back they are lacking...

[2003LimitedBanshee]

That is a very good explanation. Why do most Banshee riders prefer +4 degrees? If it fires earlier than recommended, what is the real benefit?

 

You have to think about the degrees of advance in terms of time. If you are turning 3000 RPM with your bike (not very fast I might add), the crank is making 50 revolutions per second. Now if you break down the crank rotation into degrees and you think about firing the plug 4 degrees before TDC, you are talking fractions upon fractions of seconds. So the benefit is that you start the fuel/air mix burn a little earlier. You have to realize that when the plug fires the fuel/air mix doesn't immediately fully flash and burn to provide the power stroke. In addition, because two strokes have 2 less strokes they have much shorter power strokes, meaning far fewer degrees of crank rotation before, in the case of a two stroke, the exhaust port is unmasked by the piston, the earlier you fire the mix (to a point obviously) the better. Advancing the timing helps to build torque in this case because the point at which the burn exerts more energy on the top of the piston it has greater mechanical advantage. Now, if you retard the timing, it will fire the plug later giving it slightly less mechanical advantage, but because it doesn't resist the movement of the piston it should allow for more overrev ie. higher rpm ability and power. I say it doesn't resist the piston, because technically firing it before TDC does slightly start to expand the fuel/air mix while the piston is still moving up. Remember, we are talking fractions of one second, so it is not extremely drastic. Okay, hopefully in my rambling I have made some sense and not confused myself either. Good luck...