Is The Use Of "Pump Gas" or "MoGas" Common In The Mooney World?

[GeneralT001]

I've read that Lycoming has approved many 360 engines for use with pump gas. Any issues?

[redbaron1982]

AFAIK, Mooney has not STC´d Mogas for any model. Lycoming specifically says that to legally fly with Mogas the Airframe has to be STC´d.

Oh, and one often overlooked data point: the mogas that you can use in some aircrafts has to be Ethanol free.

[bigmo]

Legally? No.

Former Rotax owner here - and for those that don't know, using 100LL in Rotax powered aircraft doubles one's engine maintenance, so we take it pretty seriously. I'm fortunate enough to live in an area of the country with ample MOGAS, so it was a rarity I had to choose 100LL (maybe 5% of my total fuel usage). But there are huge pockets of the country without access to MOGAS.

I've been following this for years, have read and listened to Swift's marketing information and honestly believe it WILL happen...but it'll be the 2030's before it happens. Not to tout California for anything good, but they'll be the first forcing function for the FAA to keep EAGLE on track and move to a single lead-free solution for all GA piston aircraft. But, that is at LEAST 5 years out (probably more). And it will take congressional action...and we all know how that will go.

Most people assume that MOGAS is cheaper than 100LL, and in some cases that's true, but more often than not, it's actually priced higher than 100LL. So, for most Rotax engine flyers, it's a quality choice they're making and has nothing to do with cost savings. I did, however, have an FBO nearby that sold unleaded 94 octane MOGAS (a Phillips product) for $3.85 a gallon. That being said, that's only a $1 cheaper than local 100LL.

I'd love to see an STC for the 360 powered Mooneys, but just don't see that happening.

On a practical note, I've lived & worked on the African continent for several years in some very austere environments. Access to AVGAS on the continent is very limited and yet the piston fleet keeps on flying. Lots of pilots operate an AVGAS tank and a MOGAS tank, some just mix and don't care. I'm also not ignorant of the vast differenced between dedicated AVGAS and running pump gas too. There are far too many variables for me to feel safe about running anything that a fleet standard in any Conti or Lyco powered aircraft. So, I'll just wait until I'm old(er).

 

 

[EricJ]

Mogas can be very difficult to find.   Most pump gasoline in the US has a lot of ethanol in it, which is outside of the requirements for the mogas STCs.   The ethanol can adversely affect seals and gaskets in the fuel system.

[Utah20Gflyer]

The O360 needs 100LL in certain conditions and when operated in a certain way.   It can run on mogas in most situations but the issue of course is when you do need it and don’t have it the consequences are generally very serious:  

The situations when you are likely to need 100LL are low elevation, hot and very high power setting.   At 12k MSL you have nice cool temps and much lower octane requirements and Mogas I’m sure would burn just fine.  

[Shadrach]

31 minutes ago, Utah20Gflyer said:

The O360 needs 100LL in certain conditions and when operated in a certain way.   It can run on mogas in most situations but the issue of course is when you do need it and don’t have it the consequences are generally very serious:  

The situations when you are likely to need 100LL are low elevation, hot and very high power setting.   At 12k MSL you have nice cool temps and much lower octane requirements and Mogas I’m sure would burn just fine.  

O360s handle mogas just fine. It’s the fuel system design that presents a challenge. Peterson offers a mogas STC for all of the following Lycoming engines, but their approval is airframe dependent.

Lycoming

0-145-A1, 0-145-A2, 0-145-B1, 0-145-B2, 0-145-B3, 0-145-C1, 0-145-C2, GO-145-C1, GO-145-C2, GO-145-C3, 0-235-C, 0-235-C1, 0-235-C1B, 0-235-E1, 0-235-E1B, 0-235-C1C, 0-235-C1A, 0-235-H2C, 0-235-C2A, 0-235-E2A, 0-235-E2B, 0-235-L2A, 0-235-L2C, 0-235-M1, 0-235-M2C, 0-235-M3C, 0-235-N2A, 0-235-N2C, 0-235-P1, 0-235-P2A, 0-235-P2C, 0-235-P3C, 0-290-A, 0-290-AP, 0-290-B, 0-290-1, 0-290-C, 0-290-3, 0-290-CP, 0-290-D, 0-290-11, 0-290-D2, 0-290-D2A, 0-290-D2B, 0-290-D2C, 0-320, 0-320-A1A, 0-320-A1B, 0-320-A2A, 0-320-A2B, 0-320-A2C, 0-320-A2D, 0-320-A3A, 0-320-A3B, 0-320-A3C, RAM 160 Conversion, 0-320-B1A, 0-320-B1B, 0-320-B2A, 0-320-B2B, 0-320-B2C, 0-320-B3A, 0-320-B3B, 0-320-B3C, 0-320-C1A, 0-320-C1B, 0-320-C2A, 0-320-C2B, 0-320-C2C, 0-320-C3A, 0-320-C3B, 0-320-C3C, 0-320-D1A, 0-320-D1B, 0-320-D1C, 0-320-D1D, 0-320-D1F, 0-320-D2A, 0-320-D2B, 0-320-D2C, 0-320-D2F, 0-320-D2G, 0-320-D2H, 0-320-D2J, 0-320-D3G, 0-320-E1A, 0-320-E1B, 0-320-E1C, 0-320-E1F, 0-320-E2A, 0-320-E2B, 0-320-E2C, 0-320-E2D, 0-320-E2F, 0-320-E2G, 0-320-E2H, 0-320-E3D, 0-320-E3H, 0-320-E1J, 0-360-B1A, 0-360-B1B, 0-360-B2A, 0-360-B2B, 0-360-D1A, 0-360-D2A, 0-360-D2B, 0-360-A1A, 0-360-A1AD, 0-360-A1D, 0-360-A1F, 0-360-A1F6, 0-360-A1F6D, 0-360-A1H, 0-360-A1H6, 0-360-A1G, 0-360-A1G6, 0-360-A1G6D, 0-360-A1LD, 0-360-A1P, 0-360-A2A, 0-360-A2D, 0-360-A2E, 0-360-A2F, 0-360-A2G, 0-360-A2H, 0-360-A3A, 0-360-A3AD, 0-360-A3D, 0-360-A4A, 0-360-A4AD, 0-360-A4D, 0-360-A4G, 0-360-A4J, 0-360-A4K, 0-360-A4M, 0-360-A4N, 0-360-A5AD, 0-360-C1A, 0-360-C1C, 0-360-C1E, 0-360-C1F, 0-360-C1G, 0-360-C2A, 0-360-C2C, 0-360-C2E, 0-360-C4F, 0-360-C4P, 0-360-F1A6, 0-360-G1A6, 0-360-J2A, H0-360-C1A, 0-435, 0-435-A, 0-435-C1, 0-435-1, 0-435-C1, 0-435-11, 0-435-C2, 0-435-13, 0-540-B1A5, 0-540-B1B5, 0-540-B1D5, 0-540-B2A5, 0-540-B2B5, 0-540-B2C5, 0-540-B4A5, 0-540-B4B5, 0-540-A1A, 0-540-A1A5, 0-540-A1B5, 0-540-A1C5, 0-540-A1D, 0-540-A1D5, 0-540-A2B, 0-540-A3D5, 0-540-A4A5, 0-540-A4B5, 0-540-A4C5, 0-540-A4D5, 0-540-D1A5, 0-540-E4A5, 0-540-E4B5, 0-540-E4C5, 0-540-F1B5, 0-540-G1A5, 0-540-G2A5, 0-540-H1A5, 0-540-H2A5, 0-540-H1A5D, 0-540-H2A5D, 0-540-H1B5D, 0-540-H2B5D, R-680-E3, R-680-E3A, R-680-E3B, R-680-9, R-680-13, R-680-E1, R-680-E2, R-680-6, R-680-B6, R-680-D5, R-680-D6, R-680-B2, R-680-BA, R-680-2, R-680-4, R-680-B4, R-680-B4B, R-680-B4C, R-680-B4D, R-680-B4E, R-680-5, R-680-7, R-680-8, R-680-11, R-680-17, R-680-B5, 0-540-F1B5 (Derated for Robinson), 0-320 Series (Derated for Robinson), 0-360 Series (Derated for Robinson)

 

[Pinecone]

There are two different major flavors of Lycoming 360 engines.  With a lot of variation in compression ratio.

O-360s are mostly parallel valve and lower compression.  180 HP.   There are parallel valve IO-360s that may run on MOGAS.  They were originally certified on 91/96 AVGAS.

The 200 HP IO-360s are angle valve and higher compression.  And I don't think any can be run on MOGAS.

[Hank]

On 9/22/2024 at 11:48 AM, Utah20Gflyer said:

The O360 needs 100LL in certain conditions and when operated in a certain way.   It can run on mogas in most situations but the issue of course is when you do need it and don’t have it the consequences are generally very serious:  

The situations when you are likely to need 100LL are low elevation, hot and very high power setting.   At 12k MSL you have nice cool temps and much lower octane requirements and Mogas I’m sure would burn just fine.  

So like leaving the beach after a week long visit in August, from 3500' grass strip . . . That's me every summer. The rental homes don't supply sheets or bath towels, and my wife can't cook without her InstaPot.

[tony]

Their is a difference in the latent heat of vaporization between Mogas and 100LL.  I believe, now this is just folklore,  during hot day testing the Mooney aircraft experienced a vapor lock.  

[Shadrach]

20 hours ago, Pinecone said:

  And I don't think any can be run on MOGAS.

Not legally but I know of a few scofflaws that have done so.  One tank of 100LL and the other 93 mogas. Climb, take-off, and landing on 100LL, cruise on mogas.  I was told that switching from 100LL to Mogas increased CHTs by 30-40° all other things being equal.  ROI seems low just to save a few bucks.

I know of someone who operated an NA C210 this way quite a bit, but for them it was more of a fuel availability issue rather than economics.

[Pinecone]

1 hour ago, tony said:

Their is a difference in the latent heat of vaporization between Mogas and 100LL.  I believe, now this is just folklore,  during hot day testing the Mooney aircraft experienced a vapor lock.  

Wrong term.  The issue is the Vapor Pressure, commonly the Reid Vapor Pressure.   This is how volatile the fuel is.  So at a given temperature, it would exert a certain pressure in a closed container.

AVGAS has a single allowable (or a small range) RVP.  MOGAS changes from season to season.  In winter the RVP is higher for easier starting in cold weather.   Since planes travel, you could fuel with winter MOGAS in MN, fly to the Keys, and try to take off on hot day with that fuel.

So the testing required a tank of the highest allowable MOGAS RVP fuel, heated to something like 120 degrees F and then a straight climb to the service ceiling.  This is the test that many low wing airplanes fail as the engine driven pump is sucking, so lowering the pressure even more that the altitude does, leading to vapor bubbles forming.  So some aircraft need a booster electric pump near the fuel tank to push the fuel to the engine.

I guess there were not enough low compression Mooneys to justify the engineering and testing for the STC.

[Pinecone]

5 minutes ago, Shadrach said:

Not legally but I know of a few scofflaws that have done so.  One tank of 100LL and the other 93 mogas. Climb, take-off, and landing on 100LL, cruise on mogas.  I was told that switching from 100LL to Mogas increased CHTs by 30-40° all other things being equal.  ROI seems low just to save a few bucks.

I know of someone who operated an NA C210 this way quite a bit, but for them it was more of a fuel availability issue rather than economics.

I have also heard of people doing this.  They REALLY fit the CB mold.

Locally 100LL is $6.32.   93 AKI MOGAS is about $4.  Lugging containers and trying to handle 50 gallons to fill one side is NOT WORTH IT TO ME.

[Shadrach]

2 minutes ago, Pinecone said:

I have also heard of people doing this.  They REALLY fit the CB mold.

Locally 100LL is $6.32.   93 AKI MOGAS is about $4.  Lugging containers and trying to handle 50 gallons to fill one side is NOT WORTH IT TO ME.

I agree.  The 210 driver I knew was not based at an airport.  He had high octane in a tank at a farm strip (this was before Ethanol was pervasive).  The Mooney driver that did it was a member here who confessed his sins privately.  Another downside mentioned was that he could smell the mogas in the cockpit when he switched tanks.

[Pinecone]

Smelling the MOGAS is not a good thing.

I can see the logic.  But be VERY sure you are on the proper tank for take off.  You could destroy your engine very quickly.

[AJ88V]

2 hours ago, Shadrach said:

Not legally but I know of a few scofflaws that have done so.  One tank of 100LL and the other 93 mogas. Climb, take-off, and landing on 100LL, cruise on mogas.  I was told that switching from 100LL to Mogas increased CHTs by 30-40° all other things being equal.  ROI seems low just to save a few bucks.

I know of someone who operated an NA C210 this way quite a bit, but for them it was more of a fuel availability issue rather than economics.

I did meet a Mooney owner in Phoenix who did exactly this. (airport not ID'd to protect the guilty)

Two thoughts:

One, avgas is unbelievably stable stuff.  After my old airport (W32) closed and I lost my hangar, my plane had to sit outside for two years unused while I got my medical straightened out.  Wings were eventually covered to protect from hail damage and maybe shielded from direct sun, but, still, sitting for two years and the gas still smelled fresh  as new and the engine fired right up.  Heck, I have some older motorcycles that can't make it through a winter without having to clean the carbs in the spring.  Avgas can sit for years, not mogas.

Two, while the engine may be fine on mogas, I have no idea about things like the tank sealant, fuel lines, gaskets, o-rings, and pump seals.  They were tested to withstand the avgas spec (ASTM D910 and DEF STAN 91-090).  Do you even know what is in the mogas you'd be buying?  Any testing done on the tank sealant, gaskets and seals?  Is the money you might save worth your life?

[Shadrach]

49 minutes ago, AJ88V said:

I did meet a Mooney owner in Phoenix who did exactly this. (airport not ID'd to protect the guilty)

Two thoughts:

One, avgas is unbelievably stable stuff.  After my old airport (W32) closed and I lost my hangar, my plane had to sit outside for two years unused while I got my medical straightened out.  Wings were eventually covered to protect from hail damage and maybe shielded from direct sun, but, still, sitting for two years and the gas still smelled fresh  as new and the engine fired right up.  Heck, I have some older motorcycles that can't make it through a winter without having to clean the carbs in the spring.  Avgas can sit for years, not mogas.

Two, while the engine may be fine on mogas, I have no idea about things like the tank sealant, fuel lines, gaskets, o-rings, and pump seals.  They were tested to withstand the avgas spec (ASTM D910 and DEF STAN 91-090).  Do you even know what is in the mogas you'd be buying?  Any testing done on the tank sealant, gaskets and seals?  Is the money you might save worth your life?

I would have zero concerns about issues with tank sealant and o-rings with mogas.  Many many STC holders operating in the field with the same gaskets, adhesives and seals. Peterson had to demonstrate compatibility to get the STC approved.

Avgas is blended to exceed shelf life specs. Technically, it’s required to meet production standards after 12months in storage. In reality, 10 year old samples that have been properly stored have shown to meet production standards. It’s lasts a long time…

 

[Will.iam]

14 hours ago, Shadrach said:

Not legally but I know of a few scofflaws that have done so.  One tank of 100LL and the other 93 mogas. Climb, take-off, and landing on 100LL, cruise on mogas.  I was told that switching from 100LL to Mogas increased CHTs by 30-40° all other things being equal.  ROI seems low just to save a few bucks.

I know of someone who operated an NA C210 this way quite a bit, but for them it was more of a fuel availability issue rather than economics.

My brain locked up on this cht’s increasing 30-40 degrees. I’m assuming this is because 100LL burns more sliwly than Mogas and thus mogas is effectively advancing the timing of the combustion event which IIRc automobile engines just retard their timing to compensate for lower octane fuel because it burns faster than higher octane fuel so what if you ran on only one set of mags which in essence slows down the burn rate would that be enough to ofset the faster burning mogas to bring the CHT’s back to normal? Just thinking out loud here. Obviously could not push too much power or the lower octane mogas would start exploding instead of burning evenly but for low power setting like cruise i wonder if running one mag would offset the lower octane fuel. 

[1980Mooney]

On 9/22/2024 at 10:35 AM, bigmo said:

Former Rotax owner here - and for those that don't know, using 100LL in Rotax powered aircraft doubles one's engine maintenance, so we take it pretty seriously. I'm fortunate enough to live in an area of the country with ample MOGAS, so it was a rarity I had to choose 100LL (maybe 5% of my total fuel usage). But there are huge pockets of the country without access to MOGAS.

Interesting comment.  We should all be clamoring for unleaded avgas.

[1980Mooney]

On 9/22/2024 at 9:44 AM, GeneralT001 said:

I've read that Lycoming has approved many 360 engines for use with pump gas. Any issues?

 

On 9/22/2024 at 9:50 AM, redbaron1982 said:

AFAIK, Mooney has not STC´d Mogas for any model. Lycoming specifically says that to legally fly with Mogas the Airframe has to be STC´d.

Oh, and one often overlooked data point: the mogas that you can use in some aircrafts has to be Ethanol free.

 

On 9/22/2024 at 12:27 PM, Shadrach said:

O360s handle mogas just fine. It’s the fuel system design that presents a challenge. Peterson offers a mogas STC for all of the following Lycoming engines, but their approval is airframe dependent.

Lycoming

0-145-A1, 0-145-A2, 0-145-B1, 0-145-B2, 0-145-B3, 0-145-C1, 0-145-C2, GO-145-C1, GO-145-C2, GO-145-C3, 0-235-C, 0-235-C1, 0-235-C1B, 0-235-E1, 0-235-E1B, 0-235-C1C, 0-235-C1A, 0-235-H2C, 0-235-C2A, 0-235-E2A, 0-235-E2B, 0-235-L2A, 0-235-L2C, 0-235-M1, 0-235-M2C, 0-235-M3C, 0-235-N2A, 0-235-N2C, 0-235-P1, 0-235-P2A, 0-235-P2C, 0-235-P3C, 0-290-A, 0-290-AP, 0-290-B, 0-290-1, 0-290-C, 0-290-3, 0-290-CP, 0-290-D, 0-290-11, 0-290-D2, 0-290-D2A, 0-290-D2B, 0-290-D2C, 0-320, 0-320-A1A, 0-320-A1B, 0-320-A2A, 0-320-A2B, 0-320-A2C, 0-320-A2D, 0-320-A3A, 0-320-A3B, 0-320-A3C, RAM 160 Conversion, 0-320-B1A, 0-320-B1B, 0-320-B2A, 0-320-B2B, 0-320-B2C, 0-320-B3A, 0-320-B3B, 0-320-B3C, 0-320-C1A, 0-320-C1B, 0-320-C2A, 0-320-C2B, 0-320-C2C, 0-320-C3A, 0-320-C3B, 0-320-C3C, 0-320-D1A, 0-320-D1B, 0-320-D1C, 0-320-D1D, 0-320-D1F, 0-320-D2A, 0-320-D2B, 0-320-D2C, 0-320-D2F, 0-320-D2G, 0-320-D2H, 0-320-D2J, 0-320-D3G, 0-320-E1A, 0-320-E1B, 0-320-E1C, 0-320-E1F, 0-320-E2A, 0-320-E2B, 0-320-E2C, 0-320-E2D, 0-320-E2F, 0-320-E2G, 0-320-E2H, 0-320-E3D, 0-320-E3H, 0-320-E1J, 0-360-B1A, 0-360-B1B, 0-360-B2A, 0-360-B2B, 0-360-D1A, 0-360-D2A, 0-360-D2B, 0-360-A1A, 0-360-A1AD, 0-360-A1D, 0-360-A1F, 0-360-A1F6, 0-360-A1F6D, 0-360-A1H, 0-360-A1H6, 0-360-A1G, 0-360-A1G6, 0-360-A1G6D, 0-360-A1LD, 0-360-A1P, 0-360-A2A, 0-360-A2D, 0-360-A2E, 0-360-A2F, 0-360-A2G, 0-360-A2H, 0-360-A3A, 0-360-A3AD, 0-360-A3D, 0-360-A4A, 0-360-A4AD, 0-360-A4D, 0-360-A4G, 0-360-A4J, 0-360-A4K, 0-360-A4M, 0-360-A4N, 0-360-A5AD, 0-360-C1A, 0-360-C1C, 0-360-C1E, 0-360-C1F, 0-360-C1G, 0-360-C2A, 0-360-C2C, 0-360-C2E, 0-360-C4F, 0-360-C4P, 0-360-F1A6, 0-360-G1A6, 0-360-J2A, H0-360-C1A, 0-435, 0-435-A, 0-435-C1, 0-435-1, 0-435-C1, 0-435-11, 0-435-C2, 0-435-13, 0-540-B1A5, 0-540-B1B5, 0-540-B1D5, 0-540-B2A5, 0-540-B2B5, 0-540-B2C5, 0-540-B4A5, 0-540-B4B5, 0-540-A1A, 0-540-A1A5, 0-540-A1B5, 0-540-A1C5, 0-540-A1D, 0-540-A1D5, 0-540-A2B, 0-540-A3D5, 0-540-A4A5, 0-540-A4B5, 0-540-A4C5, 0-540-A4D5, 0-540-D1A5, 0-540-E4A5, 0-540-E4B5, 0-540-E4C5, 0-540-F1B5, 0-540-G1A5, 0-540-G2A5, 0-540-H1A5, 0-540-H2A5, 0-540-H1A5D, 0-540-H2A5D, 0-540-H1B5D, 0-540-H2B5D, R-680-E3, R-680-E3A, R-680-E3B, R-680-9, R-680-13, R-680-E1, R-680-E2, R-680-6, R-680-B6, R-680-D5, R-680-D6, R-680-B2, R-680-BA, R-680-2, R-680-4, R-680-B4, R-680-B4B, R-680-B4C, R-680-B4D, R-680-B4E, R-680-5, R-680-7, R-680-8, R-680-11, R-680-17, R-680-B5, 0-540-F1B5 (Derated for Robinson), 0-320 Series (Derated for Robinson), 0-360 Series (Derated for Robinson)

Here is the Lycoming approved list of fuel by engine.  It includes Automotive Fuels by octane (along with Vapor Pressure and maximum oxygenate specs).

Unlike the Peterson STC list it approves unleaded Automotive fuel in certain Injected engines including some IO-360 and some IO-540.  No turbocharged engines and no IO-390.

Service Instruction No. 1070 AB | Lycoming

DATE: (lycoming.com)

[Shadrach]

3 hours ago, Will.iam said:

My brain locked up on this cht’s increasing 30-40 degrees. I’m assuming this is because 100LL burns more sliwly than Mogas and thus mogas is effectively advancing the timing of the combustion event which IIRc automobile engines just retard their timing to compensate for lower octane fuel because it burns faster than higher octane fuel so what if you ran on only one set of mags which in essence slows down the burn rate would that be enough to ofset the faster burning mogas to bring the CHT’s back to normal? Just thinking out loud here. Obviously could not push too much power or the lower octane mogas would start exploding instead of burning evenly but for low power setting like cruise i wonder if running one mag would offset the lower octane fuel. 

One could run single mag or adjust the mixture. It was ~10 years ago but my recollection of how it was described to me was that the increase in CHT was still well within the safe operating range.

[Pinecone]

4 hours ago, 1980Mooney said:

Interesting comment.  We should all be clamoring for unleaded avgas.

Yes, we should.

Lycoming already has an SB that doubles the oil change interval when running unleaded fuel.

[Pinecone]

6 hours ago, Will.iam said:

My brain locked up on this cht’s increasing 30-40 degrees. I’m assuming this is because 100LL burns more sliwly than Mogas and thus mogas is effectively advancing the timing of the combustion event which IIRc automobile engines just retard their timing to compensate for lower octane fuel because it burns faster than higher octane fuel so what if you ran on only one set of mags which in essence slows down the burn rate would that be enough to ofset the faster burning mogas to bring the CHT’s back to normal? Just thinking out loud here. Obviously could not push too much power or the lower octane mogas would start exploding instead of burning evenly but for low power setting like cruise i wonder if running one mag would offset the lower octane fuel. 

Octane does not equate to burn speed.  Octane ONLY relates to resistance to detonation.  

[N201MKTurbo]

Avgas ages well because it is mostly a single substance, alkylate. MOGAS is a witches brew of many things with different volatilities. They evaporate at different rates, so it changes composition as it ages. Some of the ingredients will oxidize and change composition. When AVGAS ages, it just evaporates but doesn’t change composition. 

[PeterRus]

1 hour ago, Pinecone said:

Yes, we should.

Lycoming already has an SB that doubles the oil change interval when running unleaded fuel.

I think it's not the interval that doubles, it's that unleaded fuel allows for synthetic (aka superior) oil and that doubles the oil change interval. 

And yes, G100UL should change the economics (engine TBO) drastically. 

Edited Wednesday at 12:53 PM by PeterRus

[N201MKTurbo]

23 minutes ago, PeterRus said:

I think it's not the interval that doubles, it's that unleaded fuel allows for synthetic (aka superior) oil and that doubles the oil change interval. 

And yes, G100UL should change the economics (engine TBO) drastically. 

Unleaded will increase the oil change interval because there is less contamination from the lead bromide. If you have good rings and little blowby, it doesn't matter.

The lead is still supplied as Ethyl Fluid which has following stuff:

Tetraethyllead was supplied for blending with raw gasoline in the form of "Ethyl Fluid", which blended tetraethyllead with the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane. Ethyl fluid contained a dye which would distinguish treated gasoline from untreated gasoline and discourage the diversion of gasoline for other purposes, such as cleaning.