Detonation Margin 8.5 vs 9 Pistons?

[rv6ejguy]

Originally Posted by Weasel

I ran 2000 or so gal of non ethenol 93 through the RV10 several years ago with 9.1 compression. Detonation was not a problem even with high ambient temp and high MAP. If I remember correctly I set the mag to 20 deg timing and adjusted the maximum available advance from 39 to about 35 which changed the entire advance curce on the electronic ignition.

I'm not following here. You were running up to 35 degrees then at low MAP?

[dlloyd3]

PA38112 brings up a good point about mogas. For most it will be a pain. Parking lot to my plane is only a hundred yards or so. Two three gallon cans is the limit. More gas or more distance or more stuff to carry is just too much. A 95 degree day will add to the misery.

[airguy]

Originally Posted by dlloyd3

PA38112 brings up a good point about mogas. For most it will be a pain. Parking lot to my plane is only a hundred yards or so. Two three gallon cans is the limit. More gas or more distance or more stuff to carry is just too much. A 95 degree day will add to the misery.

It can be a pain, yes. I have a 125 gallon stainless tank that I put a 12-volt pump on, and can carry it in the back of my pickup and lift it in/out with a chain hoist at the barn. I'm buying 91E10 locally for $3.41 that way. I did the 5-gallon jug thing as long as I could stand it.

[Canadian_JOY]

Our O-360 with stock 8.5:1 compression runs quite well on 91 Mogas. I admit that I have burned mostly 100LL during its first 70 or so hours of life, but it has demonstrated good ability to operate on various mixes of mogas/100LL as well as pure mogas.

This past weekend provided an excellent opportunity to justify sticking with 8.5:1 compression. We were far from home at a very small airport with no airports within reasonable driving or flying distance. All was fine until we pulled up to the pumps and the airport operator couldn't get the 100LL pump to work. I had enough fuel to fly to the closest alternate that had 100LL, but not with legal VFR reserves. Had we not been able to get that 100LL fuel pump to work I would have been making a trip to the local gas station out on the road to get 91 octane Mogas.

While there is no substitute for power, there is no power unless one can find fuel to burn. Keeping the lower compression pistons keeps options open for me. In this part of the country there are a lot of miles between airports - being able to fuel with whatever gas is available is of critical importance.

BTW I've hauled lots of jerry cans of fuel to the airport. Luckily I can drive right up to the hangar. My last fill up of 100LL (at that remote airport referred to above, after we managed to beat the fuel pump into submission!) cost CAD$2.25/litre or about US$5.61/gal. My previous fill-up with 91 octane Mogas cost $1.35/litre or about US$3.37/gal. That equates to about CAD$20/hour cheaper fuel-specific operating costs to run Mogas. That's a significant savings, approaching 40% - not to be ignored.

[Weasel]

Originally Posted by rv6ejguy

I'm not following here. You were running up to 35 degrees then at low MAP?

Correct. I don't remember what initial timing was at high MAP on the EI. Maybe18 or so