[Geico266]

As my mind wonders about timing an engine, I asked an A&P friend; "If 25 BTDC is optimal when running 100LL, why not time it at 28-30 BTDC when running mogas? Would this help get more power out of the engine if advancing the timing is a good thing with EI?"

This is on my 0-235 -3.

I guess I could always try it and report the results, but I thought I would ask the much more knowledgeable VAF crew first.

 

[lluciani]

Larry, I recommend that you do not try this. To prevent detonation, lower octane fuel may require that timing be retarded - not advanced.

I have a Superior XP-360. The manual requires timing to be set at 25 deg BTDC for 100LL. It recommends 22 deg BTDC for 91 octane auto fuel.

Luis Luciani

 

[asav8tor]

Luis is spot on.

Do not do it.

 

[osxuser]

100LL burns slower, therefore then spark advance being more with Avgas.

 

[Geico266]

100LL burns slower, therefore then spark advance being more with Avgas.

Ah! This advice makes sense. I guess my mind wandering can be a dangerous thing!

Thanks guys!