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-   -   Mogas vs. 100LL? (https://vansairforce.net/community/showthread.php?t=174063)

dtw_rv6 08-09-2019 01:28 PM

I used to run premium auto fuel in mine a few years back until one of my fuel injectors got closed off with some goop that I attributed to auto fuel additives. This was when I had two magnetos.

Last fall I loaded one tank with mogas for kicks... I?m now running dual electronic ignition and couldn?t for the life of me get it to run LOP without serious temp issues. I?m fine with 100LL thank you. No injector issues either.

airguy 08-09-2019 01:36 PM

Quote:

Originally Posted by dtw_rv6 (Post 1365371)
Last fall I loaded one tank with mogas for kicks... I?m now running dual electronic ignition and couldn?t for the life of me get it to run LOP without serious temp issues. I?m fine with 100LL thank you. No injector issues either.

That's most likely a timing issue - you'll need to back off the advance a bit with lower octane fuels.

TXFlyGuy 08-09-2019 01:46 PM

I was told that 93 Octane pump gas actually burns hotter, and has more energy than 100LL.

We will program our ECU Fuel MAP for 93, knowing that when we burn avgas it will be a little richer.

Also, without the lead, we will run full synthetic oil, Shell Rotella T-6.

DanH 08-09-2019 01:51 PM

Quote:

Originally Posted by airguy (Post 1365377)
That's most likely a timing issue - you'll need to back off the advance a bit with lower octane fuels.

Ditto.

Don't confuse how the spark is generated (coil control via a solid state switch rather than contact points) with the commonly too advanced timing schedules supplied by ignition vendors.

jj13 08-09-2019 02:54 PM

93UL car gas, 450+ hours
 
93UL in the right tank used for local flying and short CC. 100LL in the left tank used for landing, helps on hot starts. No mods, no issues in 4 years / 450 hours.

RVCFI 08-09-2019 03:19 PM

Mogas
 
I operate an RV10 IO540. It has 8.5 to 1 compression pistons. Would it be beneficial to put in 7 to 1 pistons at top overhaul for operations on mogas?

TXFlyGuy 08-09-2019 03:39 PM

Quote:

Originally Posted by RVCFI (Post 1365394)
I operate an RV10 IO540. It has 8.5 to 1 compression pistons. Would it be beneficial to put in 7 to 1 pistons at top overhaul for operations on mogas?

My engine has 10.8-1 compression cylinders, and it is certified to burn 92 Octane fuel.

But it is liquid cooled. So that may be the difference.

tgmillso 08-09-2019 04:49 PM

Quote:

Originally Posted by RVCFI (Post 1365394)
I operate an RV10 IO540. It has 8.5 to 1 compression pistons. Would it be beneficial to put in 7 to 1 pistons at top overhaul for operations on mogas?

If you want to do it by the book, all is detailed in the table below:
https://www.lycoming.com/sites/defau...ed%20Fuels.pdf

You will be fine if you are running high octane mogas, but if you want to run regular, according to the book you need to have the lower compression pistons. That's the beauty of this document. There's no need to speculate or listen to sob stories telling you that it's not possible, as it's all clearly stated. I think you will find that you are better off keeping the standard compression pistons and sticking with the high octane mogas, as your efficiency will reduce as you go to the lower compression ratio. David Brown has posted a chart on the forum previously clarifying this (I can't find the link at the moment) and it is not an insignificant efficiency reduction with the lower compression.
I and many others, run RON98 (Super 98) high octane (about MON91, AKI93) in an 8.5:1 IO360-M1B, as the Lycoming table stipulates, and it works amazingly well LOP and ROP. I saw no difference in my temperatures compared to running Avgas and haven't run any since my first few hours of break-in. The most important thing is that you make sure your fuel system is set up correctly to reduce any chances of vapor lock, as there may be more variability in the Reid vapor pressure of the fuels you purchase, but nothing a properly designed system can't handle. Lycoming provides the approval for the engine to run on the low octane fuel, but in the kit world we don't have STC's, so it's up to the individual builder/owner to ensure suitability of the fuel system. As has been stated before, no tight right angle bends should exist in the fuel system, make sure your lines are properly shielded from radiant heat sources (exhaust) and insulated forward of the firewall (which they should be anyway). There's heaps of info on the forum regarding this, and none of it's that difficult. Once you start running mogas you'll be wondering why for so many years you were unnecessarily squirting lead into the atmosphere making everyone as dumb as rocks and burning $$ bills you didn't need to. The next step is an all electric conversion for your RV, so none of this will be a problem in the future. Bring on the end to burning those liquified dinosaurs and my continued unintended funding of a small number of extremely rich people in the middle east.

Tom.
RV-7
IO-360M1B (until electric is available)

Capt 08-10-2019 05:58 AM

Quote:

Originally Posted by tgmillso (Post 1365406)
If you want to do it by the book, all is detailed in the table below:
https://www.lycoming.com/sites/defau...ed%20Fuels.pdf

You will be fine if you are running high octane mogas, but if you want to run regular, according to the book you need to have the lower compression pistons. That's the beauty of this document. There's no need to speculate or listen to sob stories telling you that it's not possible, as it's all clearly stated. I think you will find that you are better off keeping the standard compression pistons and sticking with the high octane mogas, as your efficiency will reduce as you go to the lower compression ratio. David Brown has posted a chart on the forum previously clarifying this (I can't find the link at the moment) and it is not an insignificant efficiency reduction with the lower compression.
I and many others, run RON98 (Super 98) high octane (about MON91, AKI93) in an 8.5:1 IO360-M1B, as the Lycoming table stipulates, and it works amazingly well LOP and ROP. I saw no difference in my temperatures compared to running Avgas and haven't run any since my first few hours of break-in. The most important thing is that you make sure your fuel system is set up correctly to reduce any chances of vapor lock, as there may be more variability in the Reid vapor pressure of the fuels you purchase, but nothing a properly designed system can't handle. Lycoming provides the approval for the engine to run on the low octane fuel, but in the kit world we don't have STC's, so it's up to the individual builder/owner to ensure suitability of the fuel system. As has been stated before, no tight right angle bends should exist in the fuel system, make sure your lines are properly shielded from radiant heat sources (exhaust) and insulated forward of the firewall (which they should be anyway). There's heaps of info on the forum regarding this, and none of it's that difficult. Once you start running mogas you'll be wondering why for so many years you were unnecessarily squirting lead into the atmosphere making everyone as dumb as rocks and burning $$ bills you didn't need to. The next step is an all electric conversion for your RV, so none of this will be a problem in the future. Bring on the end to burning those liquified dinosaurs and my continued unintended funding of a small number of extremely rich people in the middle east.

Tom.
RV-7
IO-360M1B (until electric is available)


An EP RV? I hope they invent a pill that doubles our lifespan cause you'll be using hydrocarbon Fuels for a looooooooooong time yet!:D

Pilot135pd 08-10-2019 04:48 PM

The previous owner/builder flew my plane for 400+ hours with 100LL in the right tank for takeoff and landings and 82 non-ethanol in the left tank for when he’s in cruise.

I’ve been doing the same but using 91 non-ethanol. I’ve done touch and goes on 91 with no issues except twice already if I land on 91 and shut down when I go to start it has a crazy misfire until I suppose the fuel lines get full of fuel (about 15 seconds) then it settles down to a smooth idle as normal.

Lately prices for 100LL are about the same as 91 non-ethanol so I don’t mess with it just to save $4 or $5 per tank load.


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