Trigger wheel phasing

[Aaron Silidker]

I gotcha, so I can have skip teeth of whatever, then a trigger offset of greater than 12 degrees if I want for starting? Not saying I would....but can the trigger offset be greater than a tooth plus a gap if necessary?

Also, I cannot use a timing light on this machine (could try, but it will be VERY messy, the timing mark is inside the engine), but I can extremely accurately phase the wheel to TDC.

So basically if I put the gap at 90-120 degrees it would be far enough not to affect spark and close enough to keep it very accurate. Then I could have my skip teeth as whatever amount I want for trigger offset rounded up to the next tooth subtracted from the amount of teeth between the gap and TDC. obviously, my gap position would have to be fine tuned to whatever starting advance I choose plus the amount of degrees in the other whole teeth.

I think I am starting to get it.

If I play with trigger offset afterward to see how it affects starting +/- a few degrees can I cheat the system without moving the wheel by just adding or subtracting a few degrees of timing to the entire timing table to get it all back in the correct spot?

Thanks!

[Aaron Silidker]

If using trigger rise, the MicroSquirt fires the coil on specific teeth on the trigger wheel, determined by the delay teeth (and skip teeth if you have more than one ignition event per revolution). So the only phasing requirement when using trigger rise mode is that you have a real tooth located at a point where you can fire the ignition during cranking and have it start. With a 30-2 wheel, about the only phasing I can see that couldn't work with trigger return mode is if you put the 2 missing teeth right in the best location for cranking timing, since with a tooth every 12 degrees you're almost certain to have one in the area needed for starting. Wheels with lower tooth counts might have to use calculated timing - for example, if you had a 6-1 wheel with the missing tooth location at TDC, trigger rise mode could only fire the coil 60 degrees BTDC or 60 degrees ATDC.

Do I specify what tooth it fires off of in Trigger Rise or does it fire off of the tach signal minus the trigger offset?

I guess I am a bit confused here with the logic it uses during trigger rise, specifically what parameters I set/what it sets. If you guys could clear that up I think it would help me tremendously. What kind of flexibility do I have?

I really don't think calculated is a smart choice on this engine, it is a high compression big bore single and cranking RPMs are all over the board from nearly stopped to a few hundred.

[SQLGUY]

I gotcha, so I can have skip teeth of whatever, then a trigger offset of greater than 12 degrees if I want for starting? Not saying I would....but can the trigger offset be greater than a tooth plus a gap if necessary?

Also, I cannot use a timing light on this machine (could try, but it will be VERY messy, the timing mark is inside the engine), but I can extremely accurately phase the wheel to TDC.

So basically if I put the gap at 90-120 degrees it would be far enough not to affect spark and close enough to keep it very accurate. Then I could have my skip teeth as whatever amount I want for trigger offset rounded up to the next tooth subtracted from the amount of teeth between the gap and TDC. obviously, my gap position would have to be fine tuned to whatever starting advance I choose plus the amount of degrees in the other whole teeth.

I think I am starting to get it.

If I play with trigger offset afterward to see how it affects starting +/- a few degrees can I cheat the system without moving the wheel by just adding or subtracting a few degrees of timing to the entire timing table to get it all back in the correct spot?

Thanks!

Delay Teeth... Skip Teeth is for how many times per rev you want to fire ignition. So, if TDC is 6 teeth after the missing tooth, you'd set Delay Teeth to 5 (since the default would be for the first tooth after the missing tooth to be TDC). Again, whatever this ends up being then gets the Trigger Offset applied as well. So, as you observed, you can use the Trigger Offset as the fine adjustment, and Delay Teeth as the coarse adjustment.

If you want to fire ignition twice per rev, with your 30-2 wheel, you'd set Skip Teeth to 15. If you only want to fire once per rev, set Skip Teeth to 0.

As for the timing light... can you see the trigger wheel itself when the engine is running? If so, you should be able to add a TDC timing mark to the wheel next to some fixed reference, like the VR pickup, and use that with the timing light to adjust your settings.

[SQLGUY]

If using trigger rise, the MicroSquirt fires the coil on specific teeth on the trigger wheel, determined by the delay teeth (and skip teeth if you have more than one ignition event per revolution). So the only phasing requirement when using trigger rise mode is that you have a real tooth located at a point where you can fire the ignition during cranking and have it start. With a 30-2 wheel, about the only phasing I can see that couldn't work with trigger return mode is if you put the 2 missing teeth right in the best location for cranking timing, since with a tooth every 12 degrees you're almost certain to have one in the area needed for starting. Wheels with lower tooth counts might have to use calculated timing - for example, if you had a 6-1 wheel with the missing tooth location at TDC, trigger rise mode could only fire the coil 60 degrees BTDC or 60 degrees ATDC.

Do I specify what tooth it fires off of in Trigger Rise or does it fire off of the tach signal minus the trigger offset?

I guess I am a bit confused here with the logic it uses during trigger rise, specifically what parameters I set/what it sets. If you guys could clear that up I think it would help me tremendously. What kind of flexibility do I have?

I really don't think calculated is a smart choice on this engine, it is a high compression big bore single and cranking RPMs are all over the board from nearly stopped to a few hundred.

Trigger rise uses the tach signal minus (or plus) trigger offset. But, you use Delay Teeth to set the tooth for the tach signal.

Again, with calculated, you're only in the upper left square, and maybe the one below it. These are bins that should be well outside the normal engine running area (at least the way I set things up - I use the first column as a well below idle column; idle should be in the second column and way further down in MAP). If you're running Alpha-N, though, I don't know if you get as much flexibility here.

[Aaron Silidker]

Sorry I am not getting this still. I am no dummy, I am a mechanical engineer so try not to get frustrated.

Here is where I am struggling.
1) Trigger rise...fires at a tooth so there is no calculation involved correct?
2) It will fire at whatever my tach tooth is correct?
3) Since that tach tooth cannot be at TDC for starting timing to be correct I use offset to tell the computer where TDC really is so my timing tables are correct, right?

Seeing the wheel with the engine running is pretty much 100% out of the question. This is a motorcycle and the wheel is inside the engine. There is a VERY small port that is on the engine case to see the TDC mark to set cam timing when assembling the engine, but oil will fly out if the engine is running.

Calculated is likely out of the question also since this thing is all over the place RPM wise cranking.

Thanks again!

[grippo]

Sorry I am not getting this still. I am no dummy, I am a mechanical engineer so try not to get frustrated.

Here is where I am struggling.
1) Trigger rise...fires at a tooth so there is no calculation involved correct?

>>> That is correct

2) It will fire at whatever my tach tooth is correct?

>>> Correct, and your tach teeth are (tooth 1 + Delay_teeth) and every No_skip_teeth thereafter.

3) Since that tach tooth cannot be at TDC for starting timing to be correct I use offset to tell the computer where TDC really is so my timing tables are correct, right?

>>> Some engines can start at TDC, but in general yes you use trigger offset to define where your TDC is relative to when the tach tooth is detected. So the advance you see in MT is = trigger offset during cranking and = table advance after cranking.

Seeing the wheel with the engine running is pretty much 100% out of the question. This is a motorcycle and the wheel is inside the engine. There is a VERY small port that is on the engine case to see the TDC mark to set cam timing when assembling the engine, but oil will fly out if the engine is running.

Calculated is likely out of the question also since this thing is all over the place RPM wise cranking.

Thanks again!

[SQLGUY]

Calculated is likely out of the question also since this thing is all over the place RPM wise cranking.

I can understand RPM during cranking varying between like 300 and 800. I don't see it being all over the map, nor above idle. Are you seeing cranking RPM numbers that are higher than your idle?

[Aaron Silidker]

Calculated is likely out of the question also since this thing is all over the place RPM wise cranking.

I can understand RPM during cranking varying between like 300 and 800. I don't see it being all over the map, nor above idle. Are you seeing cranking RPM numbers that are higher than your idle?

Cranking is no where near idle. Idle is at about 2000 RPM or a little less. Calculated will be ok even with a 3-400 RPM variance while cranking? Do I set the RPM where the engine is no longer cranking and it stops using start calculations or on calculated does it not even matter because it just uses the table?

[grippo]

You should set cranking rpm to the rpm at which you want to change over to table advance. Since it is hard to tell this exact point, I would set cranking rpm such that it is high enough so that you are sure the engine has caught on and doesn't need starter power and yet is below idle rpm. You want to keep it away from these limits to avoid jumping back and forth between fixed advance and table advance.

[Aaron Silidker]

Thankfully I have a big difference between the two, especially with the high compression stroker crank and piston.

Will calculated be somewhat accurate with the high resolution wheel I have and the new code?