Spark Advance safety margin for (rotary) engines that may not knock

I've watched a lot of the HPA content and find it very helpful so thanks @Andre!

I know that Andre is a strong advocate for knock detection equipment and in fact i am using a Phormula Knock KS4.

Especially with engines that get damaged very quickly when knock occurs (rotary engines) knock detection isn't very useful though.

I often hear to look out for "diminishing returns" when advancing the ignition timing but my question is:

is there some guideline to what %-power gain per 1° spark advance can be regarded as "safe"?

From my own experiences with mechanically sound piston engines i found the knock limited to be quite below the 1% power gain per 1° spark advance but especially with rotary engines, i wonder if these numbers (1% per 1°) would be a safe limit for advancing the ignition timing.

Greetings from Germany

Markus

Hi Markus, you're absolutely right - Knock detection is of limited use on rotary engines unless you're running an unbreakable apex seal and even then I'd not recommend purposely running the engine into knock. What you tend to find is that the relationship between ignition advance and torque in a rotary engine is quite flat in comparison to a piston engine so you're not necessarily leaving a lot of power on the table if you use conservative timing. Generally if I advance the timing and see no change (or minimal change) in power/torque, I'll retard the timing a couple of degrees and try again. I'm looking for that point where the power just starts to fall away. I can't say that is applicable to every rotary tuning job though as it will depend on the quality of the fuel you're using as well as the boost pressure.