Tuning Your Spark Timing Tables

[hulkss]

Spark timing is another tuning table that YOU, or a professional dyno tuner, change manually when tuning your bike. The spark table should be properly shaped for achieve good performance and no spark-knock or pinging.

Here are the rows and columns of the front cylinder spark table from H-D for a 120ST:

Here are the rows and columns of the front cylinder spark table from my bike as tuned:

This could use a little clean-up, and there are also points with less advance than the stock tune (which did not have spark knock problems). I also noticed that the front and rear cylinder spark timing was almost identical. I don't see any reason for them to be different when a performance tuner is used and the fueling is richer than stock.

So I took the most advanced timing from each tune and averaged the front and rear cylinders to get these curves:

This is looking better. I then cleaned up the curves manually being careful not to advance the timing except at dips in the curves. This is the set of curves I am running with. I get really nice smooth performance and no spark knock that I can tell (I have not logged spark knock data my PowerVision tuner to see for sure):

When you edit spark for your bike don't just change single points. Edit the curves to keep the map looking smooth and sensible and without spark-knock or pinging. The ECM can interpolate better when the curves are smooth and don't cross each other. Measured data is full of scatter and needs to be smoothed out.

 

[hulkss]

Here's the spark table that Dynojet sent me to use. Looks like a mess to me. I never did use it.

 

[NGOT8R]

Hulkss, did FM educate you on how to finetune your AFR and Spark Tables? If so, is it fair to say that you have now likely improved upon the tuning job that they recently did for you on their dyno? Your new graphs look nice and and smooth and I'm very curious to see how the new tweaks have worked out for you hp/tq wise.

 

[danoday]

Hulkss, I am not a specialist at this stuff and I respect your input and work. I am curious why you didn't like the Dynojet table, It seems to support the science rule of as the engine speed increases, you need to ignite the mixture in the combustion chamber earlier because there is less time between spark and optimum peak pressure angle.

 

[Sullyolive]

New to this. But found to be interesting.
Dyno should be calibrated before to atmosphere pressure and temp mine took 5 hrs and in between had to change atmospheric pressure. Also with exhaust gas sniffer reading emissions and comparing o2 sensor voltage thru entire process. Lot of info for me to take in but was great advice


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[hulkss]

Hulkss, did FM educate you on how to finetune your AFR and Spark Tables? If so, is it fair to say that you have now likely improved upon the tuning job that they recently did for you on their dyno? Your new graphs look nice and and smooth and I'm very curious to see how the new tweaks have worked out for you hp/tq wise.

My changes had no effect on max power or torque as I did very little to alter the wide open throttle spark timing. What I did mainly was bring the part throttle timing advance back up to where it was from my H-D street tuner. No point in giving up any spark advance if there is no spark-knock.

I'm sure the dyno operator does not have the time to manually advance the timing at every load speed condition while checking for spark knock. They mainly check timing at WOT to tune for peak power.

 

[hulkss]

Hulkss, I am not a specialist at this stuff and I respect your input and work. I am curious why you didn't like the Dynojet table, It seems to support the science rule of as the engine speed increases, you need to ignite the mixture in the combustion chamber earlier because there is less time between spark and optimum peak pressure angle.

Well yes, the curves I received from Dynojet are generally correct, however, there are a few things I did not like:

1. I don't like the way the timing is retarded as throttle is applied (increasing manifold pressure). There is a very rapid pull back in timing right at the point where you commonly roll-on the throttle to pass.
2. There is a huge change in timing from 60 to 70 kPa manifold pressure. The manifold pressure curves should be more evenly spaced.

 

[hulkss]

New to this. But found to be interesting.
Dyno should be calibrated before to atmosphere pressure and temp mine took 5 hrs and in between had to change atmospheric pressure. Also with exhaust gas sniffer reading emissions and comparing o2 sensor voltage thru entire process. Lot of info for me to take in but was great advice

The dyno operator enters conditions of barometric pressure, temperature, and humidity. The dyno software then adjusts the readings to standard test conditions so dyno performance numbers can be compared accurately when tested under different weather conditions. My bike was tuned with wideband O2 sensors in the head pipes near the exhaust ports. For me, an exhaust sniffer would not work, as I have cat-converters in the exhaust.

 

[danoday]

Did you or do you have to change the values for ion sensing knock retard or do you turn the knock control off or not even an issue?

 

[hulkss]

I think the best way to check timing is to tune the bike for fuel and air first getting the Volumetric Efficiency (VE) tables correct. Then data log looking for spark knock retard events. You then reduce timing a little where there is knock and test ride again. If there is no knock in a region of the table you think is low on spark advance, increase the timing a couple degrees and log knock retard events again.

 

[danoday]

Thanks Hulkss.

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