NefMoto > Technical > Tuning > Ignition timing
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Author Topic: Ignition timing  (Read 8411 times)
masterj
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« on: January 24, 2012, 03:52:47 AM »
Ok, another thread with another question Smiley
How would look ignition angle table if it weren't limited to knock?
I mean as RPM rises would it be same as low rpm or should go lower or higher (that is if it were in ideal environment where only power is considered)?

Please look at the image below for clarification Wink

Also when the turbo hits max boost should the timing be also maxed out at that point? (remember still ideal environment)
« Last Edit: January 24, 2012, 04:01:58 AM by masterj » Logged
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carlossus
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« Reply #1 on: January 24, 2012, 06:47:12 AM »
Very simplistically: -

The burn speed in the cylinder for a given charge will burn at the same rate no matter what the RPM
but
The increasing engine speed means that the cylinder is completing a stroke in less time
so
If everything else is equal (which it isnt in reality) the spark must happen earlier and earlier as the RPM increases in order that the same amount of charge has been burned by the time the cylinder reaches the best position (where the cylinder pressure has the maximum sum force on the crank).

So, theoretically you should advance timing as engine speed increases.

In reality though the engine is a complex system that is non linear. It's very hard to model and so it's easiest for the calibrator to sit it on a dyno and individually tweak the timing at each load point / RPM. That's why it's generally best to start from the OEM timing map because thats how it was done.

Regarding boost:
More boost = more charge = more cylinder pressure = faster burn so timing needs to be retarded, but you're usually knock limited so you can't get to peak torque anyway.
« Last Edit: January 24, 2012, 06:51:43 AM by carlossus » Logged
masterj
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« Reply #2 on: January 25, 2012, 06:57:01 AM »
Quote from: carlossus on January 24, 2012, 06:47:12 AM
Very simplistically: -

The burn speed in the cylinder for a given charge will burn at the same rate no matter what the RPM
but
The increasing engine speed means that the cylinder is completing a stroke in less time
so
If everything else is equal (which it isnt in reality) the spark must happen earlier and earlier as the RPM increases in order that the same amount of charge has been burned by the time the cylinder reaches the best position (where the cylinder pressure has the maximum sum force on the crank).

So, theoretically you should advance timing as engine speed increases.

In reality though the engine is a complex system that is non linear. It's very hard to model and so it's easiest for the calibrator to sit it on a dyno and individually tweak the timing at each load point / RPM. That's why it's generally best to start from the OEM timing map because thats how it was done.

Regarding boost:
More boost = more charge = more cylinder pressure = faster burn so timing needs to be retarded, but you're usually knock limited so you can't get to peak torque anyway.

thank you for this info Smiley Actually I'm (almost) not knock limited as my fuel is E85 and peak torque should be reached before knock happens

BTW: KFZW vs KFZWOP maps. If I understand everything then it means that KFZWOP(1-2) is the map to change instead of KFZW(1-2) since ecu stars at KFZW degrees and goes up until KFZWOP is reached unless knock is encountered. Am I right about this? Or should I change KFZW(1-2) maps instead?
« Last Edit: January 25, 2012, 07:09:49 AM by masterj » Logged
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fredrik_a
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« Reply #3 on: January 25, 2012, 08:06:01 AM »
Quote from: masterj on January 25, 2012, 06:57:01 AM
thank you for this info Smiley Actually I'm (almost) not knock limited as my fuel is E85 and peak torque should be reached before knock happens

For E85, you will most certainly reach maximum torque before knock.
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phila_dot
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« Reply #4 on: January 25, 2012, 08:56:50 AM »
Quote from: masterj on January 25, 2012, 06:57:01 AM
thank you for this info Smiley Actually I'm (almost) not knock limited as my fuel is E85 and peak torque should be reached before knock happens

BTW: KFZW vs KFZWOP maps. If I understand everything then it means that KFZWOP(1-2) is the map to change instead of KFZW(1-2) since ecu stars at KFZW degrees and goes up until KFZWOP is reached unless knock is encountered. Am I right about this? Or should I change KFZW(1-2) maps instead?

No, that is not how KFZWOP is used.

The only applications I see for KFZWOP(2)'s output (zwopt) is in various forms of intervention (torque, charge, lambda, and ignition angle).

Typically ignition angle efficiency is determined by the difference zwbas and zwist from zwopt into ETADZW. If actual ignition angle efficiency strays from target ignition angle efficiency (result of torque intervention or KR) then various forms of intervention can be enabled.

The output from KFZWOP is used for calculation of ignition angle efficiency. This is used in torque calculation and coordination along with numerous other forms of intervetion.

It is typically calculated as follows:

zwopt - zwbas into ETADZW

Or

zwopt - zwist into ETADZW

Or

(zwopt - zwgru into ETADZW) - (zwopt - zwist into ETADZW)

Any variance from 1 - 9 degrees is 99% efficiency. I try to stay within that range.
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masterj
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« Reply #5 on: January 25, 2012, 09:07:31 AM »
Quote from: phila_dot on January 25, 2012, 08:56:50 AM
No, that is not how KFZWOP is used.

The only applications I see for KFZWOP(2)'s output (zwopt) is in various forms of intervention (torque, charge, lambda, and ignition angle).

Typically ignition angle efficiency is determined by the difference zwbas and zwist from zwopt into ETADZW. If actual ignition angle efficiency strays from target ignition angle efficiency (result of torque intervention or KR) then various forms of intervention can be enabled.

The output from KFZWOP is used for calculation of ignition angle efficiency. This is used in torque calculation and coordination along with numerous other forms of intervetion.

It is typically calculated as follows:

zwopt - zwbas into ETADZW

Or

zwopt - zwist into ETADZW

Or

(zwopt - zwgru into ETADZW) - (zwopt - zwist into ETADZW)

Any variance from 1 - 9 degrees is 99% efficiency. I try to stay within that range.


So what happens if KFZW has bigger values than KFZWOP? :O

BTW: Isn't KFZWOP originally filled with OPTIMAL (MAX POWER) igition angles? So theoretically I could just copy values from these tables to KFZW?
« Last Edit: January 25, 2012, 09:35:06 AM by masterj » Logged
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phila_dot
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« Reply #6 on: January 25, 2012, 11:27:44 AM »
Quote from: masterj on January 25, 2012, 09:07:31 AM
So what happens if KFZW has bigger values than KFZWOP? :O

100% ignition angle efficiency

Quote from: masterj on January 25, 2012, 09:07:31 AM
BTW: Isn't KFZWOP originally filled with OPTIMAL (MAX POWER) igition angles? So theoretically I could just copy values from these tables to KFZW?

Theoretically yes. I wouldn't advance that much at once though.
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masterj
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« Reply #7 on: January 25, 2012, 11:58:24 AM »
Quote from: phila_dot on January 25, 2012, 11:27:44 AM
100% ignition angle efficiency

Theoretically yes. I wouldn't advance that much at once though.

Got it! Thanks
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