I have an MX7-235 with the io-540-W1A5D and according to Swift fuel STC, it appears this engine and my model aircraft, are eligible.

I am wondering the following:

Has anyone. Gotten the STC, and run the fuel for a while?
Which engines?
What is different from a performance standpoint?
What are the benefits?
What are the downsides?

There are a few areas near me that have banned 100LL and now are only offering 94UL (that’s a whole other topic) and having options is always good.

While I support the elimination of TEL from avgas, I watch with justifiable concern as to the formulation they come up with to replace the existing universal fuel. I worked in the automotive industry for a couple of decades and saw firsthand what the original formulation of unleaded auto fuels did to the rubber components in cars (ever seen liquified rubber on a fuel pump?). To see that issue manifest itself in aviation would be a serious disaster. Also knowing that the rubber composition of most of our aviation fleet is of that vintage places us at a serious risk. With that said, I also believe that backwards compatibility with our rubber components is a paramount qualification for replacement fuel as a result of what we saw happen to cars in the early 80's. So there is some faith they did consider that. The automotive industry also made modifications to the rubber chemistry in affected fuel system components that hasn't happened in aviation because getting permission to make such a change triggers the STC process for thousands of parts industry wide (what a cluster that would be...).

Being in TX, I have been able to find only one airport selling Swift's UL94 in the state (Dublin, TX) and it's not along the way of my usual routes, otherwise I would be willing to guinea pig myself with it as my 4 cylinder Lycoming also complies with their STC.

I was speaking the other day with a fellow who said he'd used this stuff in his 172 since it has been out and not had trouble of any kind. He said he saw no difference in performance or engine management. He claims he does what he's always done, and gets the same result he's always gotten. He's a pretty accomplished aviation guy and a good guy. So I trust his word. Admittedly it's not the big motor like you've got, but at least it's some input.

Please keep this list informed if you do try it. I'd really like to know how it goes.

Thanks for the thoughts and I spoke with a mechanic friend who echo the same concerns with gaskets, seals, rubber etc and I really hope the UL/Swift has made the effort to make it equal to 100LL. I plan on calling lycoming to ask specifically about their thoughts.

I have heard performance wise, it works well in big bore, engines, low compression. Higher compression/tight tolerances might be somewhat more finicky. All hearsay at this point, but please keep the feedback coming as this I believe will be an inevitable journey….

I have been running it exclusively since September. I have had no problems with it. So far it has worked fine. I have an M4 with an O-360 C1F. For airplanes that can use it, it works great. It is totally wrong and politically motivated to replace 100ll with it as Reid Hillview and San Martin have done. My home airport, Watsonville CA still has 100LL in addition to UL94. I use the UL94 but I think we absolutely need to stand up for our friends that still need 100LL until a 100 octane unleaded becomes available. There is some info here.

https://www.savereidhillview.org/post/u ... advantages

I spoke with Lycoming this Am and they provided me some info:

I have the two files (SL270 and SI1070AB) in a dropbox folder since it doesn't appear we can attach documents here (I might have missed something).
https://www.dropbox.com/sh/8btidxvr52ik ... QfI3a?dl=0

looks like for certain engines, the UL94 extends the TBO and Lycomimg recommends that when you switch fuels, you do an oil change. I have not read through the docs yet, but sounds like for those that can, switching may have some benefits.


@SPIFF I am based @KWVI as well, and parked in transient till they give me a permanent spot (can't miss the plane as it is only one on amphibs). We should meet up sometime and chat Maule's. I agree with you in helping our compatriots at Reid hillview and south county.

So am I reading that SI correctly where it shows the O-540-J that many of us fly behind is compatible with ALL the fuel types shown in that document per table 3 on page 7?

Just want to make sure I didn't miss anything. I think the -J, specifically the Maule's O-540-J1A5D is considered "high(er) compression" hence limited to 2400 RPM compared to the lower compression models that can go to 2700 RPM. That said, I always assumed we'd be in trouble once the unleaded fuels were adopted but maybe that's not the case based on this documentation.

I am by no means and authority or mechanic on this subject, but my understanding is that the 540’s are considered low compression engines. My understanding from my years of following maules is that the O-540-J are auto gas capable (several variables here.) My other understanding is that ethanol for any of these engines is not good.

When in doubt, call Lycoming. They were very helpful. For my specific questions on the IO-540.

a lot of good info here:

https://www.swiftfuelsavgas.com/faq

Availability of 94UL will be the snag. California airports will probably adopt it sooner than others due to different state or county environmental standards. Although FBOs will be able to mix 94UL and 100LL, they won't be able to sell it except to aircraft with the STC and low compression engines. That's going to be too complicated for most FBOs and I doubt they will want to spend the money to install separate tanks and pumps.

The most feasible distribution method, at least initially, will be separate fuel trucks. However, FBOs won't spend the money for them unless they can recover the cost through fuel sales or if they get public funding. The FAA's Airport Improvement Program will likely include projects like this in the future but it may take some time since the process of getting AIP grants is not quick. AIP grants are also available only to publicly owned airports.

Economics will likely drive the switch to UL fuel. A combination of AIP grants and higher fuel prices for 94UL or 100UL (when it is approved) from separate fuel trucks seems like the most feasible approach. Eventually, 100UL will be available for all aircraft including high-compression engines so I expect most FBOs to offer only 100UL rather than both 94UL and 100UL. However, the necessity of buying the STC will slow down its adoption. The FAA could speed up the adoption by dropping the STC requirement but I can't see them doing that until safety data for several years are available.

I believe Andy is correct in his analysis. The M7 235 B I was able to buy last year has the 0540 low compression engine and the previous owner had installed the Maule STC for Mo gas. This works very well for me as I keep it on a private strip where I have a portable tank with 93 or 91 ethanol free mo gas. This is the sixth airplane I have run mo gas in over the last 35+ years ( one 150 hrs past TBO) with no problems and have saved a lot of money on fuel and maintenance. The key seems to be test fuel for ethanol every time you buy and only buy what you will use up in four or five months and buy 100ll on long trips or periodically to get some lead mixed in. The old 80 these engines were certified with had 1/4 th the lead as 100ll. The Maule STC is expensive but if you fly enough hours it will pay. Years ago when on a public airport I had a 100 gal tank in back of pickup. My daddy use to say “ there’s a lot of ways to skin a cat”.

I recently picked up the STC for the IO540-W1A5D. Will let you know how the switch over, maintenance, and performance changes over the next few months.

Please do as I have the same motor.

Tim

Same for me, I’ll be interested to hear also

Seems odd that you'd need an STC, for $100, to get pilots to use, and someday soon force, in GA aircraft.