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  #1  
Old 02-03-2021, 09:37 PM
Kuhtenia Kuhtenia is offline
 
Join Date: Jan 2018
Location: Galena, Ohio
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Default Lycoming “O” versus “IO” Approved Automotive Fuels

Came across Lycoming Service Instruction No. 1070AB (dated 4/8/2020), “Specified Fuels for Spark-Ignited Gasoline Aircraft Engine Models” (https://www.lycoming.com/sites/defau...ed%20Fuels.pdf). [Document is technical and irrespective of separate FAA certification considerations.]

Question is this – For automotive fuels that meet Lycoming specs, Table 3 of the document ("Fuels and Fuel Grades Approved for Use in Lycoming Engine Models") includes many of the “O” variety engines, but relatively fewer of the “IO” engines. Is there a particular technical reason for this, is it more about what has actually been tested over the years, something else?
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  #2  
Old 02-03-2021, 11:29 PM
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skylor skylor is offline
 
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Location: Southern California
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Default Compression Ratio

Quote:
Originally Posted by Kuhtenia View Post
Came across Lycoming Service Instruction No. 1070AB (dated 4/8/2020), “Specified Fuels for Spark-Ignited Gasoline Aircraft Engine Models” (https://www.lycoming.com/sites/defau...ed%20Fuels.pdf). [Document is technical and irrespective of separate FAA certification considerations.]

Question is this – For automotive fuels that meet Lycoming specs, Table 3 of the document ("Fuels and Fuel Grades Approved for Use in Lycoming Engine Models") includes many of the “O” variety engines, but relatively fewer of the “IO” engines. Is there a particular technical reason for this, is it more about what has actually been tested over the years, something else?
Most if the IO-360 series excluded from the auto fuel columns have higher compression ratios (8.7:1) than the O-360 (8.5:1). Th IO-390 which is also excluded has an 8.9:1 CR.

I’m not too familiar with the -540 models but I assume the IO models that are excluded is also due to higher compression ratio.

Skylor
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  #3  
Old 02-04-2021, 04:31 AM
Avanza Avanza is offline
 
Join Date: Jul 2020
Location: Vastervik Sweden
Posts: 140
Smile Automotive fuel

It is all about the copression ratio and the different combustion cambers.
If you are looking at the IO-360 there are two completely different engines.
1. the angle valve IO-360 compression ratio 8,7, 200 hp or more.
2. the parallell valve IO-360 compression ratio 8,5, 180 hp.
I have the parallell valve IO-360 compresson ratio 8,5, 180 hp and
using autofuel for more than 10 years with no problems.
This engine is also sold as the O-360 with carburator 180 hp.

Good luck
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  #4  
Old 02-04-2021, 05:33 AM
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rv6ejguy rv6ejguy is offline
 
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By limiting timing at high MAP, you can safely run Mogas in any naturally aspirated Lycoming with standard compression ratios. You may have a loss in maximum power at higher manifold pressures but cruise performance should be unaffected.

This is best addressed with an EI having user programmable timing curves rather than fixed timing mags.
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  #5  
Old 02-04-2021, 08:16 AM
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Raymo Raymo is offline
 
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The Peterson STCs (one airframe, one engine) I applied to my Cherokee 140 (O-320-E2D) stated the primary concern with MoGas is vapor lock, which could be dealt with by turning on the boost pump.
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Last edited by Raymo : 02-04-2021 at 11:08 AM.
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  #6  
Old 02-04-2021, 09:15 AM
Freemasm Freemasm is offline
 
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Default Depends.

Haven’t read that particular STC; however, usually one each is required for airframe and power plant. Making a low wing airframe acceptable for Mogas is typically not a complex undertaking. A high wing often takes zero modification to hardware or operation. It is important to consider/differentiate between the two; AF and PP.

Last edited by Freemasm : 02-04-2021 at 09:18 AM.
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Old 02-04-2021, 09:45 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by Freemasm View Post
Haven’t read that particular STC; however, usually one each is required for airframe and power plant. Making a low wing airframe acceptable for Mogas is typically not a complex undertaking. A high wing often takes zero modification to hardware or operation. It is important to consider/differentiate between the two; AF and PP.
For mogas, that's generally true - but for car gas with ethanol, caution is advised. The ethanol blends will not play nicely with natural rubber compounds in the fuel system like O-rings, hoses, bladders or diaphragms. You'll need to replace those with Viton or Teflon.

It's not actually the ethanol that attacks the rubber - but ethanol is an octane booster, which allows the refinery to start with a lower-quality base stock and still get to the same target octane after they add the ethanol. That lower-quality base stock has more aromatic hydrocarbon rings like benzene and related compounds, and those are what will attack the rubber.
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  #8  
Old 02-04-2021, 12:49 PM
Avanza Avanza is offline
 
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Location: Vastervik Sweden
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Smile Mogas with ethanol

Lycoming introduced fluorosilicone rubber in their fuelinjection 1987.
This is compatible with ethanol blended fuel.
I have a IO-360 parallel valve compression ratio 8,5, 180 hp.
Previously I had the Lazar electronic magnetoes with large spark advanse running with no problem. Now I have the Surefly (2) with 25 deg + spark advance up to 38 deg working fine.
I have not seen any reduction in power or increased fuel consumption.
There is about +5 F higher CHT compared to 100 LL.
CHT is around 320-350 F and never goes higher than 400 F.
Cylinders and pistons are very clean.
Mogas in EU may not be produced to the same standard as Mogas in the US.

Good luck
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  #9  
Old 02-04-2021, 01:38 PM
Freemasm Freemasm is offline
 
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Quote:
Originally Posted by airguy View Post
For mogas, that's generally true - but for car gas with ethanol, caution is advised. The ethanol blends will not play nicely with natural rubber compounds in the fuel system like O-rings, hoses, bladders or diaphragms. You'll need to replace those with Viton or Teflon.

It's not actually the ethanol that attacks the rubber - but ethanol is an octane booster, which allows the refinery to start with a lower-quality base stock and still get to the same target octane after they add the ethanol. That lower-quality base stock has more aromatic hydrocarbon rings like benzene and related compounds, and those are what will attack the rubber.
Yes Sir. My brief and poorly worded response was specific to the RVP property. The typical engine in the subject Piper has no problem with the lower Octane. As I’m sure you know, that’s only the half of it. Most people who’ve been around long enough have at least heard of improper use of Mogas/car gas/pump gas/. sometimes with very bad consequences. Here in the states (and probably everywhere) fuel is still the cheapest thing you put in an aircraft.
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  #10  
Old 02-04-2021, 03:17 PM
Kuhtenia Kuhtenia is offline
 
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Thanks for the various pieces of information, all. Appreciate it.
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