How an ignition timing curve relates to the timing curve of the time between ignition and 12*ATDC. Here's my listing of 2 stroke videos: dragonfly75.com/moto/my2Tvide...
I failed to mention why it seemed correct that the chart curve of time from ignition to 12*ATDC gave a similar curve to that of the time from TDC to exhaust port opening at different RPM. 1) Most CDI are very similar with their timing curves and that can't be a coincidence, it has to be because that is what works best. 2) That typical curve that I charted out had the same curve progression that the chart for time from TDC to exhaust opening had which has to have some significance. 3) It's obvious that the typical CDI timing curve is superior to fixed timing or else CDI's would be made with set timing also.
I wouldn't of thought that a hump-backed timing curve would of given a time-to-peak-compression curve that matched the TDC-to-Exhaust Opening curve. But it does and that convinces me that it is correct. Logical people look out for little tips toward the truth when the truth isn't obvious. I know, I know, I should just be more trusting and not question things that are known to work. But I have to know why they work and what is their hidden synchronicity with the laws of physics.
I have a 77 RD400C that I rebuilt back to stock. I love these motors stock, chambers and airbox removal destroys low/mid power making them a chore to drive around town. I did add a Vape ignition but it still has a flat ign curve of 10 degrees I think it is but these bikes make so much more torque with a proper curve. My plan is to buy programmer unit but I still need to find a dyno so I can find a curve that's good but safe. There are no dynos in my smallish city sadly.
@@MichaelForrestChnl Hi.. I replaced the points with a Vape ignition. I did have an HPI on it that had a 'safe' curve and the bike really made good power with it but the flywheel was tiny and almost weightless and I really didnt like the way the bike felt at lower rpm.. and having to keep a higher idle as well to prevent it from stalling. The chunky Vape flywheel makes the bike feel miles smoother. Perhaps I should just program in the same curve the HPI has and be happy with that.
Hi very interesting on ignition timing I don’t know if you have come across ignitec ignitions I have one fitted onto my 250 race bike for roadracing with a programmable map as I understand from you 30 degrees before tdc for high reviving 2 strokes or am I not understanding correctly
the final say so is how your bike runs. Just try different settings. As fas as the highest ignition advance for mid range RPM if a certain range of settings feels the same then choose the least advancement.
Your timing curves go down after a certain point. Are these engines boosted? Are you trying to maintain a specific cylinder pressure? Trying to reduce power a higher rpm? For what purpose? Is the engine starvi g for fuel? In a car engine, given that enough fuel and naturally aspirated, curves typically incline to infinity at a diminishing rate as rpm goes up. Even with boost you should have a lower overall timing but it should still climb.
that is typical for an analog CDI which is why most CDI's are not analog. If the timing is kept from diving down at top RPM then more over-rev is possible.
When you say boosted well in a way they are, 2 strokes rely heavily on exhaust resonance, (and inlet resonance) when they are 'on-the-pipe', the volumetric efficiency (VE) of the engine will go up well past 100% This increase in VE will increase the initial pressure in the cylinder (the pressure BEFORE the plug fires), this increases the flame speed which means that you need to retard the timing so that the peak cylinder pressure occurs at the right point in the power stroke, certainly NOT at TDC as some idiots on youtube claim! If the pipe has a tuned length of lets say 9k RPM then the timing will retard more and more as it get near 9k because the pipes is working nearer and nearer in designed PRM. once past 9k the pipe starts to work slightly less well so the timing can start to advance from that point onwards as the VE of the engine is falling. People that like to talk nonsense will talk about retarding the timing to increase the pipe temperature, this is all secondary, its VE and flame speed that are important. (Heating the pipe will change its resonant frequency RPM). The other thing to note that in simple terms as the revs rise you would think that the timing would advance, well it would have to if the VE remained the same but it 'goes through the roof when the engine comes onto the pipe' hence the odd looking ignition 'curve' that you see in this video. Finally 2 strokes are quite fussy when it comes to timing, a 2 stroke in a reasonable state of tune likes nothing better than to either seize or blow a hole in a piston, an over advanced timing gives it just the excuse that it needs!
I failed to mention why it seemed correct that the chart curve of time from ignition to 12*ATDC gave a similar curve to that of the time from TDC to exhaust port opening at different RPM. 1) Most CDI are very similar with their timing curves and that can't be a coincidence, it has to be because that is what works best. 2) That typical curve that I charted out had the same curve progression that the chart for time from TDC to exhaust opening had which has to have some significance. 3) It's obvious that the typical CDI timing curve is superior to fixed timing or else CDI's would be made with set timing also.
I wouldn't of thought that a hump-backed timing curve would of given a time-to-peak-compression curve that matched the TDC-to-Exhaust Opening curve. But it does and that convinces me that it is correct. Logical people look out for little tips toward the truth when the truth isn't obvious. I know, I know, I should just be more trusting and not question things that are known to work. But I have to know why they work and what is their hidden synchronicity with the laws of physics.
I have a 77 RD400C that I rebuilt back to stock. I love these motors stock, chambers and airbox removal destroys low/mid power making them a chore to drive around town. I did add a Vape ignition but it still has a flat ign curve of 10 degrees I think it is but these bikes make so much more torque with a proper curve. My plan is to buy programmer unit but I still need to find a dyno so I can find a curve that's good but safe. There are no dynos in my smallish city sadly.
A standard timing curve will get you within 95% of "the best" timing. Does it have points ignition?
@@MichaelForrestChnl Hi.. I replaced the points with a Vape ignition. I did have an HPI on it that had a 'safe' curve and the bike really made good power with it but the flywheel was tiny and almost weightless and I really didnt like the way the bike felt at lower rpm.. and having to keep a higher idle as well to prevent it from stalling. The chunky Vape flywheel makes the bike feel miles smoother. Perhaps I should just program in the same curve the HPI has and be happy with that.
Hi very interesting on ignition timing I don’t know if you have come across ignitec ignitions
I have one fitted onto my 250 race bike for roadracing with a programmable map as I understand from you 30 degrees before tdc for high reviving 2 strokes or am I not understanding correctly
the final say so is how your bike runs. Just try different settings. As fas as the highest ignition advance for mid range RPM if a certain range of settings feels the same then choose the least advancement.
Is this from a Dyno pull or from a reading on a tach with a program?? How to get similar stats?
those are just for illustration purposes, to teach you about what each adjustment does to the flame speed which affects the power
how can i identify that cdi will delay while reaching 6,000rpm to 9,500rpm?
only by timing light dragonfly75.com/motorbike/timinglight.html
Your timing curves go down after a certain point. Are these engines boosted? Are you trying to maintain a specific cylinder pressure? Trying to reduce power a higher rpm? For what purpose? Is the engine starvi g for fuel? In a car engine, given that enough fuel and naturally aspirated, curves typically incline to infinity at a diminishing rate as rpm goes up. Even with boost you should have a lower overall timing but it should still climb.
that is typical for an analog CDI which is why most CDI's are not analog. If the timing is kept from diving down at top RPM then more over-rev is possible.
When you say boosted well in a way they are, 2 strokes rely heavily on exhaust resonance, (and inlet resonance) when they are 'on-the-pipe', the volumetric efficiency (VE) of the engine will go up well past 100% This increase in VE will increase the initial pressure in the cylinder (the pressure BEFORE the plug fires), this increases the flame speed which means that you need to retard the timing so that the peak cylinder pressure occurs at the right point in the power stroke, certainly NOT at TDC as some idiots on youtube claim! If the pipe has a tuned length of lets say 9k RPM then the timing will retard more and more as it get near 9k because the pipes is working nearer and nearer in designed PRM. once past 9k the pipe starts to work slightly less well so the timing can start to advance from that point onwards as the VE of the engine is falling. People that like to talk nonsense will talk about retarding the timing to increase the pipe temperature, this is all secondary, its VE and flame speed that are important. (Heating the pipe will change its resonant frequency RPM). The other thing to note that in simple terms as the revs rise you would think that the timing would advance, well it would have to if the VE remained the same but it 'goes through the roof when the engine comes onto the pipe' hence the odd looking ignition 'curve' that you see in this video. Finally 2 strokes are quite fussy when it comes to timing, a 2 stroke in a reasonable state of tune likes nothing better than to either seize or blow a hole in a piston, an over advanced timing gives it just the excuse that it needs!