90 AKI mogas in engine requiring 91AKI

AV8R_87

AV8R_87

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This is my problem. Considering getting the STC, but I don't have a convenient source of 91 AKI E0 gas. There are a few places selling 90 within a reasonable driving range.

What can I do? Mixing the 90 mogas in a 9:1 ratio with 100LL seems to bring the overall AKI to 91 or above, even when using worst-case RON/MON numbers for both. The STC allows mixing fuels, but not sure if it would meet the legal requirements which specify 91 AKI gas.

Anything I could use as an octane booster that would be safe for an aircraft fuel system? Any other ideas?
 
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There are various octane boosting and dives available, but alcohol alone boasts octane. So you have to be careful.
 
You would think an STC allowing pump gas would include fuel system modifications to allow alcohol blends. E0 is a pretty restrictive requirement, certainly in this state.
 
Ethanol blends are such a mess, though.

I'd only do ethanol gas in a plane if it was fuel injected with submerged fuel pumps in the tanks.

That way the fuel pump churns any water that might be present back in the alcohol/gas mix, and it won't clog up the injectors like it would a carb jet.

Plus, with a submerged pump you don't have to worry about vapor lock.
 
Xylenes or Toluene would do the trick. Paint store, assuming they still sell ‘em. I used to blend my own high-octane unleaded with it to race Turbo Buicks while keeping the O2 sensor alive. I believe it was about 3 gallons per tankful to get a bit over 100 (R+M)/2. That was 20+ years ago and I’m getting old, so better do your own math…
 
If you're not gonna store it long term, I can vouch for the fact that 1786822995064.png. Oh you're welcome! anytime! :thumbsup:
 
Mixing fuel strikes me as a more defensible choice compared to a DIY VOC cocktail. Also, toluene is nasty and will probably eat your paint if you spill any.

This stuff does not seem to contain alcohol or toluene: https://race-gas.com/ ; I don't know anything about it.

I've been running E0 in my O200 for a while. I've heard that pump gas is less stable but I have not observed any ill effects. I have observed that pump gas seems to be less kind to o-rings (fuel drain valves) and also seems to be less kind to paint. I would probably be better off if I ran a mix of 100LL, but that sounds like more work.

Just be sure to use the correct ratio, since you will surely spontaenously combust and auger into an orphanage if you're off by one AKI.

Sac Arrow said:
You would think an STC allowing pump gas would include fuel system modifications to allow alcohol blends. E0 is a pretty restrictive requirement, certainly in this state.
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I would not. E0 is "only" a paper $TC, fuel $ystem mod$ are more expen$ive.

cc:
@Capt. Geoffrey Thorpe
@PaulMillner
@chemgeek
 
GeorgeC said:
This stuff does not seem to contain alcohol or toluene: https://race-gas.com/ ; I don't know anything about it.
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They seem to use a couple things to get octane - Oxygenates (they don't say which ones, but EBTE is a typical one and what Swift and VP/Lyondell seem to be using). The second is Manganese, or more specifically, methylcyclopentadienyl manganese tricarbonyl or MMT. I recall GAMI mentioning some issues with MMT in avgas, but don't recall what they are.

So no aromatics (toluene, etc.) in their additive.

They do specifically prohibit using their stuff in aviation.
 

From Race-Gas.com FAQ:​

I noticed that my spark plugs have an orange dust on them after running RACE-GAS in my tank. Are my plugs fouled or scorched? ​

No! The dust you are seeing is the byproduct of burning fuel with manganese.
 
Hang 4 said:
They seem to use a couple things to get octane - Oxygenates (they don't say which ones, but EBTE is a typical one and what Swift and VP/Lyondell seem to be using). The second is Manganese, or more specifically, methylcyclopentadienyl manganese tricarbonyl or MMT. I recall GAMI mentioning some issues with MMT in avgas, but don't recall what they are.

So no aromatics (toluene, etc.) in their additive.

They do specifically prohibit using their stuff in aviation.
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Phillips 66 blowded-up the lawnmower at PAFI when their manganese brew seized the test cell. They exited the competition thereafter. Turns out paint thinner was the real daddy sauce lol.

Oxygenates seems to be the one the FAA will go with by the looks of it. Can't make rich setting 130 tho, paint thinner can do.
 
I would bet 1 AKI is within the error bars of the AKI test.
 
My GSXR 750 called for 90 AKI. We don't have 90 here, so it's either 89 or 91. It ran perfectly fine on 89.

The 1200RT on the other hand called for 91. It could handle 89 (or even 87 I think) but the knock sensor and timing retard would kick in and you would get a noticeable loss of power and economy until you ran a tank or two of 91.
 
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