Spark advance curves

[John Appel]

We are now at the stage of testing our 1200cc twin cylinder motorcycle engine. We have the use of a computer controlled load bearing dyno, chain driven from the gearbox sprocket. At this point we have achieved a reasonably good fuel map.We are using a single spark advance curve set for full throttle at this early stage of tuning. Spark advance is at 32 degrees from 3500rpm upward. As a next step we are thinking of  using just three advance curves for different throttle settings. Can anyone suggest suitable throttle setting points to choose. I had in mind about 10% and 30% and 100% but I have no previous experience of this and so would welcome any suggestions. Also how much extra advance should I use at the lower throttle settings.Does anyone have a spark map for a similar engine. Details are 600cc per cylinder, 4 valves per cylinder, compression ratio  9.5 to 1, air cooled.  A BMW boxer would be a good example.

 Regards, John

[sardengineering]

Good day.

Your proposed points sound okay based on the big increases of air flow into the engine relative to throttle opening. So to have break points to cover the range of big increases in VE would be best based on what you are asking.

Ignition advance is influenced on fuel and bore diameter in addition to what you've already listed. I would either use the onboard knock windowing of the G4+ or the Link Knock Block so that you can listen to the combustion event as it happens making adjustments based on the feedback you get.

The is an extremely interesting project, if you can, please leave a few photos in the customer car section of the forum. It's great to see the Link brand utilized in such a diverse manner.

Cheers!