Why does my POH say to use 91/96 octane avgas

[McMooney]

REading my poh, it very clearly says i can use 91/96 octane fuel.  wth

[EricJ]

If you can find some you can use it!

 

[Hank]

6 hours ago, McMooney said:

REading my poh, it very clearly says i can use 91/96 octane fuel.  wth

Because that's what was available and recommended when your plane was built. You circled in blue the 4 fuels that used to be widespread, sadly now there is only the one. 

[Pinecone]

But it does mean, you maybe could buy the STC and use Swift fuels 94UL, if someone around you carries it.

And you may be able to use the 91UL that the FAA is talking about blanket approval for.  If you can find someplace selling it.

Or you can use 100LL.   Or buy the STC and use G100UL, once it starts pumping.

[N201MKTurbo]

I was at Watsonville CA last week. They had UL95. It was $1.00 more than 100LL.

[PT20J]

Pretty sure the engine was certified to use that fuel. 

[Pinecone]

2 hours ago, N201MKTurbo said:

I was at Watsonville CA last week. They had UL95. It was $1.00 more than 100LL.

I have seen reports of that.  They have to recover the cost of the tank and pump and EPA stuff, for selling a lot less gallons.

[AIREMATT]

11 hours ago, McMooney said:

 

Just to be clear, it doesn’t mean use premium 91 octane car gas.

[MBDiagMan]

When was that POH printed?  Has avgas gone through a few changes since then?

[A64Pilot]

56 minutes ago, MBDiagMan said:

When was that POH printed?  Has avgas gone through a few changes since then?

Yes, not a single one of the listed fuels is still available.

It’s similar to oil, some people particularly with older Dirsels get real concerned because they cant find the oil the manual says use, because that spec has been superseded.

[A64Pilot]

6 hours ago, Pinecone said:

I have seen reports of that.  They have to recover the cost of the tank and pump and EPA stuff, for selling a lot less gallons.

Yeah they say that at first, but I have never seen the new fuel come down, UL car gas, ULSD whatever, it’s always higher and stays that way

[Hank]

31 minutes ago, A64Pilot said:

Yeah they say that at first, but I have never seen the new fuel come down, UL car gas, ULSD whatever, it’s always higher and stays that way

Sure, because it's new. When KFC brought out Extra Crispy, it cost more; then they discontinued Original Recipe  only to bring it back later at a price higher than Extra Crispy . . . . . 

When would avgas be any different???

[MikeOH]

This talk of gasoline and Extra Crispy in an aviation context is making me nervous!! 

[RLCarter]

It doesn’t say use 91/96, it says Never use Aviation fuel lower than that… 100LL is most of us only choice 

[JayMatt]

buy some ethanol free 93 octane at buccee's dump a jar of lead based octane booster in it and be on your way. 

What's the difference between aviation gas and pump gas aside from the octane rating? 

 

PP thoughts only, don't listen to me. 

[Pinecone]

9 minutes ago, JayMatt said:

buy some ethanol free 93 octane at buccee's dump a jar of lead based octane booster in it and be on your way. 

What's the difference between aviation gas and pump gas aside from the octane rating? 

 

PP thoughts only, don't listen to me. 

Vapor pressure for one.   AVGAS has a single vapor pressure no matter where you buy it or what season.  Mogas varies as to climate and season.  One reason that many low wing aircraft have to have modifications to fuel system to deal with northern winter mogas that is still in your tank when you are arriving in FL.

Pump gas octane on the pump is AKI, which is the average of MON and RON.  You have NO indication of what the actual MON is, which is basically the same as the AVGAS Grade.  There is no standard for the spread of MON to RON.  Typically, top tier fuels are kept to a spread of not more than 10 points, but that is NOT required.

So that 93 mogas you buy, 88 MON, but it could be less.  That is OK on an engine rated for 80/87 (the 80 is the MON), but not so good for an engine rated for 91/96.

Where are you finding lead based octane boosters?  All the ones that are commonly available use a "lead substitute."  And unless you are adding actual tetra ethyl lead, you are now a test pilot.  Oh, and as a double whammy, many of those octane boosters and alcohol based.

Oh, and you are also operating illegally, as your TDCS does not approve use of mogas.  So unless you have an STC for mogas, you are both a test pilot and flying an aircraft the FAA and most IAs would consider not airworthy.

[Andy95W]

Look at his last line, he was joking.

Great explanation of AKI, MON, and RON though.

[EricJ]

3 hours ago, JayMatt said:

What's the difference between aviation gas and pump gas aside from the octane rating? 

And all the wack additives that turn mogas into goo if it sits for very long.   

[A64Pilot]

It’s a little more complicated than that.

in this example 91 is the octane rating / resistance to detonation in “aviation lean”

96 is the rating in “aviation rich”

I put the lean and rich in parenthesis because I can’t explain them precisely except to say that rich mixtures are more detonation resistant.

https://club.mobilindustrial.com/glossary-of-lubrication-terms/w/glossary-of-terms/568/lean-and-rich-octane-number#:~:text=lean and rich octane number - expression of the antiknock value,air-fuel mixtures%2C respectively.

So why is 100LL only one number when it meets the old 100 / 130 spec? I don’t or can’t answer that because I don’t know.

So in other words Auto fuel Octane rating and Avgas Octane rating can’t be compared unfortunately. It really is apples and oranges despite the same name.

Oh, and I don’t think you can buy Tetra Ethyl Lead in an Octane booster unfortunately, probably easier to buy Uranium than TEL.

 There are ways most of us could burn Mogas, technology from way back before WWII, but then so are our engines.

I can’t see $12,000 though, surely that would come down if it gets more widely used

https://www.aviationconsumer.com/uncategorized/airplains-inpulse-adi-mogas-for-big-engines/

https://www.avweb.com/features/the-return-of-anti-detonation-water-injection-adi/

[A64Pilot]

3 hours ago, EricJ said:

And all the wack additives that turn mogas into goo if it sits for very long.   

Yes, but take Avgas and just leave the lead out of it, and run ADI.

I think 100LL with no lead added is 94UL? The ADI fluid is cheap and you don’t use much and surely if you do nothing but leave the lead out of the fuel it ought to be a little less expensive? If you don’t get silly you wouldn’t even need to do anything with the trucks and tanks etc, just simply start using the UL fuel and pretty soon the lead amount would be nearly zero.

I hate to say problem solved, but why wouldn’t it be?

[Pinecone]

7 hours ago, Andy95W said:

Look at his last line, he was joking.

Great explanation of AKI, MON, and RON though.

We need to start like BT and jokes in Green font.   Or at least put a smiley.

Thanks.  I learned a lot of the topic from the car world and fighting the ignorance.  A number of years ago I found a great article online by a petroleum engineer for Shell.  He drove a Corvette.

The funny thing was, we spent decades getting people to under stand that no, putting high octane (or AKI) fuel in your car will not increase performance.  Only to now have all the whizz bang controls in modern cars that many times you will get better performance with high octane/AKI fuel.  In some cases only in certain conditions but other cars, all the time.  My E46 M3 gives max performance at about 96 AKI.  Below that, even normal pump premium, you are losing performance.  But only at or near full throttle. 

BTW, most race tracks have pumps with 98 AKI unleaded fuel.  It makes AVGAS look cheap.   But for my car, for track days, I run about a 50/50 mix of 93 and 98, slightly biases to 98.  So right around 96.  You can feel the difference.   

My 1995 E36 M3 Lightweight has a Conforti chip, and it runs MUCH better on 98 race gas.

[Pinecone]

43 minutes ago, A64Pilot said:

Yes, but take Avgas and just leave the lead out of it, and run ADI.

I think 100LL with no lead added is 94UL? The ADI fluid is cheap and you don’t use much and surely if you do nothing but leave the lead out of the fuel it ought to be a little less expensive? If you don’t get silly you wouldn’t even need to do anything with the trucks and tanks etc, just simply start using the UL fuel and pretty soon the lead amount would be nearly zero.

I hate to say problem solved, but why wouldn’t it be?

STC for ADI system.  Cost of ADI system.  Cost of installing ADI system.  Reduced useful load from ADI system.

Chance of pilot forgetting to fill ADI system, or no fluid available and being engine out at 200 - 300 feet on takeoff.

Also, the Red Box or Red Fin will be larger for running in cruise without the ADI.

But it is available.  https://www.avweb.com/features/the-return-of-anti-detonation-water-injection-adi/

[T. Peterson]

8 hours ago, Pinecone said:

Vapor pressure for one.   AVGAS has a single vapor pressure no matter where you buy it or what season.  Mogas varies as to climate and season.  One reason that many low wing aircraft have to have modifications to fuel system to deal with northern winter mogas that is still in your tank when you are arriving in FL.

Pump gas octane on the pump is AKI, which is the average of MON and RON.  You have NO indication of what the actual MON is, which is basically the same as the AVGAS Grade.  There is no standard for the spread of MON to RON.  Typically, top tier fuels are kept to a spread of not more than 10 points, but that is NOT required.

So that 93 mogas you buy, 88 MON, but it could be less.  That is OK on an engine rated for 80/87 (the 80 is the MON), but not so good for an engine rated for 91/96.

Where are you finding lead based octane boosters?  All the ones that are commonly available use a "lead substitute."  And unless you are adding actual tetra ethyl lead, you are now a test pilot.  Oh, and as a double whammy, many of those octane boosters and alcohol based.

Oh, and you are also operating illegally, as your TDCS does not approve use of mogas.  So unless you have an STC for mogas, you are both a test pilot and flying an aircraft the FAA and most IAs would consider not airworthy.

So what’s the problem??

[A64Pilot]

40 minutes ago, Pinecone said:

STC for ADI system.  Cost of ADI system.  Cost of installing ADI system.  Reduced useful load from ADI system.

Chance of pilot forgetting to fill ADI system, or no fluid available and being engine out at 200 - 300 feet on takeoff.

Also, the Red Box or Red Fin will be larger for running in cruise without the ADI.

But it is available.  https://www.avweb.com/features/the-return-of-anti-detonation-water-injection-adi/

Chance of pilot running out of oil or fuel? ADI will have low level sensors. Oil doesn’t, even if you did, when the empty light comes on, reduce to 25” MP and return and fill the tank.

ADI operates whenever detonation is possible, above 25” MP and or cyl head temps above 400. For an NA engine that shouldn’t be an issue for cruise. Turbo’s may or may not need another answer. Do you cruise over 25” and or 400 cyl head temp?

The STC shouldn’t be above $5 or 6K as a guess and as there isn’t any kind of patent there would be several STC’s if or once it catches on.

I don’t think there is yet a Mooney STC, just ones for aircraft that often worked where Avgas was scarce, unless it’s changed.

[A64Pilot]

11 minutes ago, T. Peterson said:

So what’s the problem??

There are other issues, first Ethanol is prohibited, and non ETH fuel can be hard to find. Phase separation is one good reason 

But it’s been years ago but I searched the NTSB database long and hard looking for an accident that the cause was Auto fuel and couldn’t find one, maybe I just wasn’t searching correctly, or maybe they are almost non existent?