Fuel Tank Placard

[Auburntsts]

So, I have an IO-540-C which, IAW Lycoming SI 1070R, was certifed to use a minimum grade of 91/96 AVGAS (which is no longer available, at least in CONUS). I need to gen up the fuel tank placards (or possibly engrave the fuel caps -- haven't decided) and I'm wondering if I should just put down "100LL" or should I put "91 OCT MIN" or something similar in case by some miracle one of those unleaded, 90ish octane 100LL substitutes becomes a reality? Of course, this is more of an issue if I go the engraved route. What say the brain trust?

[rleffler]

I had my caps engraved with 100LL.

If the fuel standard changes, it's cheap enough to get replacement caps covers. You don't have to replace the entire mechanism. I actually have a polished set ready to swap out when I have some free time.

This was almost a ding on my inspection. He was so used to see the large decals around the the fuel cap, he didn't noticed the engraved caps. However, once he saw them, he liked them a lot.

[Auburntsts]

Yeah, I know, but for once I just wanted to try and get ahead of the game.

[hydroguy2]

That's what I did. Just in case i want to run autofuel.

[BobTurner]

Be careful! Av gas is measured using the 'motor' octane test. Autogas uses the average of the 'motor' and 'research' tests. 91 octane car gas is lower than 91 octane av gas.

[Auburntsts]

Good point, and SI 1070R covers this. But it's important to look up the approved fuels for your engine all Lycomings are not created equal in this matter. For example, according to the SI and my operators manual, my 540 is not approved for mo-gas at all, regardless of octane. It's AVGAS or nothing, at least as far as I have been able to find in writing.

EDIT: Although I wonder if an STC is out there for it? And if there is, would Lycoming include that in their documentation? OF course I may just be showing my ignorance of how STCs work, which is entirely possible since I've never really concerned myself with such things before now.

[Neal@F14]

I recommend putting the minimum octane number on the cap or placard, that way you legally covered for whatever fuel is equal or greater than that, and then you can decide what grade fuel you're comfortable running in your engine (for when the day comes that 94UL avgas becomes available, or if you're comfortable running 91 octane mogas, or whatever).

[flyboy1963]

My 0-320 is placarded on the data plate something like
" Min. Octane 80/87"

so I figured by tank labels are correct if they say the same thing.

that said, I also hope that should accident investigators come upon a pile of aluminum, and sump the tanks, they should find the 'correct' minimum octane, be it mogas or avgas, and not have reason to unduly suspect that cause.

But, what does the engine builder guy do when he puts in Hi-compression pistons?..... is the data plate removed and replaced, modified, or just noted in the engine log?

[N427EF]

Unless you are trying to maintain a certified engine status you can put whatever you want or more precisely whatever you have tested in your experimental plane.
Mine runs happily on 91 Octane E10 mogas in all phases of flight, tested in over 100F without a hiccup.
Only 200 hours so far and no sign of any engine or fuel system problems.
I have a very precise EI MVP 50 engine monitor with full recording capability and frequently check
engine operating parameters to make sure nothing is out of ordinary operating limits.
Aero Sport IO 540 AFP injection 1 mag 1 magneto 8:1 CR.

[hydroguy2]

Originally Posted by Neal@F14

I recommend putting the minimum octane number on the cap or placard, that way you legally covered for whatever fuel is equal or greater than that, and then you can decide what grade fuel you're comfortable running in your engine (for when the day comes that 94UL avgas becomes available, or if you're comfortable running 91 octane mogas, or whatever).

Exactly. I only run 100LL in my 9:1 engine, but I have the option of adjusting the timing and running autofuel if I chose.