Just one more mogas thread. Desperately sorry.

[docmirror]

For the sake of giggles, lets say that a guy has a plane, with an electric fuel pump mounted near the Tee from a dual fuel tank setup. There was also a mechanical fuel pump in the normal location on the Lyc engine and the engine was mounted about 4 feet ABOVE the fuel tanks. On a pylon, as it were. There is no excess return line as in some fuel systems.

The engine is supplied with fuel from the tank via the electric pump for starting and take off, then the electric pump is switched off, and the fuel is supplied by the mech engine driven pump except for emergencies.

The fuel lines are of good design, with no 90deg bends(the one Tee fitting), and remain out of the engine bay except for the last 2.3 feet from the mech pump to the carb.

The engine is a standard 4 cyl air cooled variety of 8.5:1 C/R, not angled valve.

A. Would you run 91 Octane mogas given this situation?

B. If yes, would summer or winter(conditions, fuel blends) make a difference?

C. A dual electronic ignition with detonation detection is avail, and could be fitted, would that make a difference in using mogas? Up to 6deg retard in two stages, but it reduces power by about 3-5%, and would be in operation at the most critical time(take off, full power).

D. This almost purely an exercise in economy, although my experience has been that many engines run better on mogas, with an occasional tank of 100LL from time to time. Would it be worth the testing? Modifying?

 

[JHW]

Summer vs winter is probably the only parameter that matters in your hypothetical scenario. But the you'll never know until you test it.

 

[docmirror]

I thought of something else. There are two tanks, one is 21 gallons, the other is 12.5. I could envision keeping 100LL in the 12.5 for take off and aux, and should anything go wrong, and use the 21 tank for cruise where optimum performance is not an issue.

 

[JHW]

Pick an airport at random. Walk up to the first 310 or baron that you see. Take a cap off a main tank and take a whiff. Do the same with an aux tank. Check the next similar plane in line. It won't take long to find one where the mains smell sweet and the aux tanks stink.