[airguy]

I'm having a set of PV cylinders overhauled in anticipation of doing a top end on my 9A, currently running 8.5 compression and burning 93E10. During my testing with that setup I satisfied myself that I have at least 3 degrees of ignition protection in my detonation margin with this setup, I'm curious who in the fleet here might be running auto pump gas with 9:1 and what timing they are using? I have a guy bending my ear about using 9:1 pistons on the overhauled cylinders, my gut response is to avoid it - but the engineer in me wants a little data if available for the decision rather than emotion.

My best guess is that I would need to retard about 2 degrees across my whole ignition map when moving from 8.5 to 9 compression ratio, and then retest my detonation margins from there. Any real data from the crowd?

 

[Freemasm]

I'm having a set of PV cylinders overhauled in anticipation of doing a top end on my 9A, currently running 8.5 compression and burning 93E10. During my testing with that setup I satisfied myself that I have at least 3 degrees of ignition protection in my detonation margin with this setup, I'm curious who in the fleet here might be running auto pump gas with 9:1 and what timing they are using? I have a guy bending my ear about using 9:1 pistons on the overhauled cylinders, my gut response is to avoid it - but the engineer in me wants a little data if available for the decision rather than emotion.

My best guess is that I would need to retard about 2 degrees across my whole ignition map when moving from 8.5 to 9 compression ratio, and then retest my detonation margins from there. Any real data from the crowd?

Maybe reach out to toobuilder. I believe he has some extensive experience with fuel type and advance, both flying and on a dyno. Don't remember what CR he's got but it's a start.