MicroSquirt.com read only forum (Jan.15,2018)

Hi All,

Can anyone help explain how to work on the deg of Injector delay based of cam timing specs?

Basically the cam timing is as follows;

Intake cam
Opens on the intake stroke 25° before TDC
Closes on the intake stroke 61° after BDC

Exhaust Cam
Opens on the Exhaust stroke 64° before BDC
Closes on the Exhaust stroke 15° after TDC

Tach 1 timing:

crank timing provided by a 36-2 wheel with the tach 1 tooth being on the tooth #31( ie the 31st tooth after the 2 missing teeth) which is actually located 5 deg BTDC ( so i am using 5 deg timing offset for base timing. )

Tach 2 timing

The engine is an odd fire timing of 0 - 300- 720 , so tach 2 is 60 deg advanced from tach 1


I would like to start injection just after the Exhaust Valve closes.

Thanks

John

Since you have a 20 degree delay between the trigger tooth, and on a 2 cylinder you have a 360 degree delay between spark events on an even fire engine, you'd need a 20/360 = 6% delay.

Matt Cramer wrote:Since you have a 20 degree delay between the trigger tooth, and on a 2 cylinder you have a 360 degree delay between spark events on an even fire engine, you'd need a 20/360 = 6% delay.

Update on Data:

* I now have the tach tooth 5 deg ATDC not 5deg BTDC

Questions:

1) Can you explain in more detail where the 20 deg comes from ?

2) Can you explain why you refer to "even fire" when it is an "Odd fire" motor?

3) Can you explain in more detail the theory of what you are trying to achieve?

4) Can you explain how your advised setting relates to the cam timing provided and my objective to have the injectors fire once the exhaust valve closes?

Cheers
Norzilla

Hi Norzilla, have you seen this thread. I don't have a V twin, but I thought injector delay was a time interval from your tach tooth, which maybe you can tweak to reach your ideal position. Check the link out below.

http://www.microsquirt.com/viewtopic.php?f=31&t=23362

With the existing code the injector start delay is referenced to the tach pulse whether it is even or odd-fire. I have a software version that corrects for odd-fire engines, but I haven't finished testing and documenting it. This documentation will include all the variables involved in setting up dual spark engines.

Norzilla wrote: Update on Data:

* I now have the tach tooth 5 deg ATDC not 5deg BTDC

Questions:

1) Can you explain in more detail where the 20 deg comes from ?

The angle between the tach tooth and the exhaust valve closing. With your new update, it would be 10 degrees instead of 20.

2) Can you explain why you refer to "even fire" when it is an "Odd fire" motor?

The delay is a percentage of what the crank angle between teeth would be on an even fire engine. Then it's shifted by the odd fire angle, I believe.

3) Can you explain in more detail the theory of what you are trying to achieve?

1. Find the angle between when you want the injector to fire (in this case, the exhaust valve closing) and the #1 trigger tooth.
2. Divide this angle by (720 / number of cylinders).
3. Convert this to a percent.

4) Can you explain how your advised setting relates to the cam timing provided and my objective to have the injectors fire once the exhaust valve closes?

Cheers
Norzilla

I hope I answered it with #1 and #3, let me know if I didn't.

With current code, Its not shifted by the odd fire angle. The inj events are always going to be 360* from each other. (unlike the ignition) So if you set #1 up to fire when the exhaust valve closes, #2 will be firing 60* after valve closes on #2. (#2 will always be 60*later than #1 in relation to valve timing). Or if you set it for #2 to fire when valve closes, #1 will be 60* earlier and fire when exhaust is open. The delay moves them both the same degrees. You have to find a happy medium, knowing this.

Tach 1 is first tooth after missing. (+delay teeth). Don't confuse tach with tdc 1 & 2.

Whats the delay teeth set to?

Why the late injection timing? Your already missing alot of air at that point. Why not something like 180 and 120 before intake opening?

800vtwin wrote:With current code, Its not shifted by the odd fire angle. The inj events are always going to be 360* from each other. (unlike the ignition) So if you set #1 up to fire when the exhaust valve closes, #2 will be firing 60* after valve closes on #2. (#2 will always be 60*later than #1 in relation to valve timing). Or if you set it for #2 to fire when valve closes, #1 will be 60* earlier and fire when exhaust is open. The delay moves them both the same degrees. You have to find a happy medium, knowing this.

Tach 1 is first tooth after missing. (+delay teeth). Don't confuse tach with tdc 1 & 2.

Whats the delay teeth set to?

Why the late injection timing? Your already missing alot of air at that point. Why not something like 180 and 120 before intake opening?

I am using delay tooth = 31 on a 36-2 wheel, making the tach tooth the #32 tooth after the missing teeth. This gives me an offset to TDC of -5 deg ie tach tooth is 5 deg ATDC.

Given the cam timing above what do you suggest as a starting point for the % delay?

Has this engine been running? If so, are you using wasted spark? Just wondering if your out 360*? You have a cam sync?

Change the delay teeth to 0. Set your trigger offset to -60. TDC #1 is 60* before tach right? (tdc, 3 teeth, 2 missing then tach tooth)?

With 0 delay teeth, you would have 310 degrees to play with injection delay. with 31 delay teeth - inj is happening at tdc.

800vtwin wrote:Has this engine been running? If so, are you using wasted spark? Just wondering if your out 360*? You have a cam sync?

Change the delay teeth to 0. Set your trigger offset to -60. TDC #1 is 60* before tach right? (tdc, 3 teeth, 2 missing then tach tooth)?

With 0 delay teeth, you would have 310 degrees to play with injection delay. with 31 delay teeth - inj is happening at tdc.

The Engine has been running. It runs sequential spark and has a cam sync that occurs during the missing teeth as expected.

Sorry to tell you, but the setting you suggest for delay tooth is not a valid setting! You see, what they don't tell you in the manual is that you can not have the missing teeth occur between TDC and the tach tooth on the same cycle, as the missing teeth and cam sync events reset the tooth counter that allows the calc of the spark advance timing. #2 cyl fires not fire in the correct position. I had to find out the hard way, i tested every permutation of delay tooth and offset +ve & -ve to work out what was going on and why the motor would only fire on the #1 cyl.

Hence the only teeth that are valid teeth for the tach 1 on my motor due to the position of the missing teeth relative to TDC are real tooth no's 32, 33, 34. Now to get to the most accurate timing you need the tach tooth within 1 tooth of TDC ( due to the maths in the code) so tooth 32 it is and the offset needs to be -ve or the timing wanders.

So given this info what do you suggest re Injector delay?