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Angle head IO-360 or IO-390 and 94UL

Carl Froehlich

Well Known Member
The first domino for 100LL going away has fallen (the current California 100LL banning). The approach is viable as I do not see the FAA or the EPA engaging in a “local issue”. In other words the 100LL replacement can has been kicked down the road as far as it will go.

I note with interest the remarkable FAA turnaround this last year to grant STC approval for a bunch of engines to run GAMI 100UL. All well and good other than the projected price. Current estimate is ~$1 more than 100LL but considering track records of such things I would guess much closer to $2 more. For us slobs still paying for our own flight hours, $7+ a gallon may tip the scales to walk away.

Swift 94UL avgas is available now, and is expanding to step in to more markets. It is cheaper to produce than 100LL and has none of the transportation restrictions associated with leaded fuel. In a free market it would be selling today at a significant discount to 100LL.

My question. Swift 94UL has been demonstrated to be a very good fuel for parallel valve Lycoming engines (8.5 to 1 pistons), with many advantages over 100LL. Does anyone know of real engine test data that can demonstrate if angle head (8.75 to 1 pistons) Lycoming engines can be configured to run on 94UL? I assume some change in timing or such will be required but I’m just guessing. If Lycoming has this test data they are not sharing it.

Thanks,
Carl
 
I don't see any press on cal banning 100LL. I see a lot a noise about reid hillview and a lot of noise about folks lobbying the EPA. However, we have discussed this and currently only the FAA, not the EPA, regulates aviation fuel. The EPA can bark all they want, but can do nothing about it. Only political pressure on the FAA Administrator from the president (He can fire him at any time, as Trump showed us) or a court ruling (likely a tough battle) will change that and I don't see the FAA banning 100LL without SERIOUS pressure. GA is the current pathway for most all of our commercial pilots. Once that comes out, it becomes startegic to the country to maintain GA and without a viable alternative to 100LL, it will continue to be sold; Lest we will see a SERIOUS commercial pilot shortage.

Have to bone up on constitutional law, but pretty sure a state cannot outlaw something that is in the federal domain and most airports are controlled by the FAA; At least those getting funding. This is why the local gov't folks cannot shut down Reid for another 10 years, when the govt agreement expires (the FAA's deal with them).

Maybe you could /post some details on this
 
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Avgas

Glad to see someone mention Reid Hillview. My personal belief is that the FAA will cave as they did on Santa Monica and that Reid will close sooner than ten years.
Equally concerning is Whiteman in LA. Whiteman is owned by Los Angeles County. The Los Angeles City Council voted unanamously to close Whiteman. How does the city of Los Angeles get to close a county owned airport. Further, there are two more airports owned by the County of Los Angeles. Will they go the way of Whiteman. Where will 5-600 airplanes go?
There are a number of airports across the country that are in the $8.00 range for 100LL $6.00 will be the end for me.
 
91E10

Carl,
Bringing up mogas isn't popular on this forum and hardly anybody mentions it anymore.
91E10 doesn't solve everybody's fuel problems but 8:5 to 1 compression ratios certainly run very happily on mogas.
Lots of us are using it but no one is posting about it anymore.
Closing in on 800 hours and more than 10 years of flying on 91E10.
 
Don't know what 702 is. Is that their 94UL or 100UL product?

Whoops, my bad. It was measured at 104.4 MON. Not was Carl was asking about.

To be frank, I've never paid much attention to the Swift data in this report. The gold is in the reams of 100LL data, FBO and minimum standard.
 
Still looking for data on if/how and angle head Lycoming engine (8.75 to 1 pistons, non turbo) can be configured to run on 94UL avgas.

I don’t have and angle head engine, but know of many RV-14 guys interested in this as 100LL price is hitting “ouch” numbers, and the holy grail 100UL drop in replacement looks to be much higher.

As a side note, I have experimented with 93 octane ethanol free mogas in parallel valve Lycoming engines. Engine runs fine, but the reduced vapor pressure is problematic so I never go beyond a 50/50 mix with 100LL. I’d burn 94UL if I could get it.

Carl
 
Watched an interesting podcast last week on SocialFlight with George Braly of GAMI. Seems like LOTS going on in the background between California and FAA (logjam of fuel approvals broken, STCs being approved for most aircraft). Worth a watch.

One point George makes is that even though his fuel is expected to be $1/gal more expensive, the increased oil change intervals spark plug servicing intervals need to be factored in. Maybe not the full $1/gal, but a substantial amount.
 
Can't find the specifics at the moment, but a San Francisco area airport isn't allowing the sale of 100LL, just the sale of 94UL.

So it's a backdoor banning of 100LL
 
100LL in Santa Clara county, CA

Can't find the specifics at the moment, but a San Francisco area airport isn't allowing the sale of 100LL, just the sale of 94UL.

So it's a backdoor banning of 100LL

OK, just so everyone is clear on this. It is NOT the state of California eliminating 100LL. It is the county of Santa Clara, banning sale of 100LL at the two county owned airports, Reid Hillview (RHV) and San Martin (E16), after December 31, 2021. Only 94UL and Jet A will be sold at these airports after the first of the year.

Some background:
This is the latest in a long long list of efforts by Santa Clara county to close RHV. Prior to this, the county stopped accepting FAA grant money for use at RHV. That started the clock on when the airport can be closed by the county. Now, after having done a lead exposure study on kids in the area surrounding RHV, the idea has been floated (at a county board of supervisors meeting) to close the airport sooner. (We can debate the validity and conclusions of the lead study......but that's a whole separate issue.) Stay tuned for future developments.

Personal opinion on:
Santa Clara county really does not want to be in the airport business.......and is looking for ways to get out of the business. Like I mentioned above, they have been looking at ways to close RHV for a loooooong time. Noise, safety, and now lead have all been used as "justification" to close it. The real reason.....probably the value of the real estate under RHV if it were to be converted to housing. Whatever the reason(s), several generations of county supervisors from the area surrounding RHV have made closing an issue.
Personal opinion off.

So, I've switched to using 94UL, whenever I swing by Watsonville (WVI) to get it, (otherwise, buying 100LL). Same price as 100LL, at least at WVI. After the first of the year, I'll be able to get it at my home airport, E16. Don't know what the guys with high compression engines are going to do, except buy 100LL at Watsonville (WVI), San Jose (SJC), Palo Alto (PAO), Hollister (CVH), or somewhere else.
 
(8.75 to 1 pistons, non turbo) can be configured to run on 94UL avgas.
What exactly needs to be "configured" to make the 8:75 to 1 angle vale be happy with 94UL?

As a side note, I have experimented with 93 octane ethanol free mogas in parallel valve Lycoming engines. Engine runs fine, but the reduced vapor pressure is problematic so I never go beyond a 50/50 mix with 100LL. I’d burn 94UL if I could get it.
Reduced vapor pressure in 93 or 91 octane mogas is obvious but what exactly did you (experience) as "problematic" in you experimentation with a50/50 mix?

It seems to me that hemming and hawing about the non availability of a 100LL replacement and the potential need for re configuring the fuel system or engine
compression ratios is a whole lot more trouble than making minute adjustments if any, to your fuel system so your engine will run reliably on 91E10.
One thing we can count on here in CA, cities and municipalities have figured out how to ban the sale of 100LL. Your options are shrinking and 91E10 is available at every corner gas station.
 
Mogas vapor pressure don't seem to be too much of an issue in reality. We have at least one customer flying around 18,000 feet regularly in the summer without issues. Proper fuel system design is a must.

With programmable variable spark timing EIs, you can retard timing easily at high MAP to avoid detonation without compromising performance at typical cruise MAPs.
 
vapor Pressure

The problem is not REDUCED vapor pressure, it is HIGHER vapor pressure of autofuel. The higher the vapor pressure, the more the fuel wants to vaporize, therefore develop gas vapor bubbles in the fuel and essentially boil. Avgas vapor pressure is low, and therefore unlikely to boil even at the very low atmospheric pressure at high altitudes and high fuel system temperatures.


What exactly needs to be "configured" to make the 8:75 to 1 angle vale be happy with 94UL?


Reduced vapor pressure in 93 or 91 octane mogas is obvious but what exactly did you (experience) as "problematic" in you experimentation with a50/50 mix?

It seems to me that hemming and hawing about the non availability of a 100LL replacement and the potential need for re configuring the fuel system or engine
compression ratios is a whole lot more trouble than making minute adjustments if any, to your fuel system so your engine will run reliably on 91E10.
One thing we can count on here in CA, cities and municipalities have figured out how to ban the sale of 100LL. Your options are shrinking and 91E10 is available at every corner gas station.
 
Original question still stands, is there any data on running an angle head IO-360 or IO-390 engines with standard 8.75 pistons on 94UL avgas (not mogas) - with some confidence that the engine will not go into detonation. If so, what was done to engine configuration?

8.75 is not much more than the parallel valve engines (8.5 pistons) that run well on 94UL, but I suspect I don’t know all the issues.

Higher compression and/or turbo engines are beyond the scope of this specific query.

Carl
 
Mogas vapor pressure don't seem to be too much of an issue in reality. We have at least one customer flying around 18,000 feet regularly in the summer without issues. Proper fuel system design is a must.

Indeed.

I don't even have problems when the fuel is heatsoaked on the ramp in 100+F temperatures, then takeoff and climb directly to those altitudes at max power. I know I'm levelling in the upper teens well before the hot fuel in the tanks has had a chance to fully cool down to local ambient, but I've never had a hiccup. I've done this with both 91E10 and 93E10, I'm running fuel rail pressure of 43-44 psig.

Now I'll say this - before I had the SDS system that keeps high fuel pressure all the way up to the injector face, back when I was still running a standard Bendix injection setup, then yes I did have a couple occassions that I could say were likely related to hot fuel vaporizing at high altitude in the climb, probably in the divider and spider lines to the injectors where the pressure was lower. After the servo I believe the pressure in a standard Bendix setup is about 6 psig, and after the divider close to zero. With SDS and EFII you get the full fuel rail pressure all the way to the injector face.

I've had my airplane up to FL210 on 91E10 without issues. Here is one screenshot from FL190 with a DA of 21000. Vapor pressure is not the issue.
 

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... Does anyone know of real engine test data that can demonstrate if angle head (8.75 to 1 pistons) Lycoming engines can be configured to run on 94UL? I assume some change in timing or such will be required but I’m just guessing. If Lycoming has this test data they are not sharing it.

Thanks,
Carl

The IO-360 angle valve has a CR of 8.7:1, while the IO-390 is 8.9:1.

Skylor
 
The IO-360 angle valve has a CR of 8.7:1, while the IO-390 is 8.9:1.

Skylor

I did not know that. It puzzles me why the combination of higher displacement AND the higher CR does not produce more power.

390/360 * 200= 216 even at the same CR.
With a CR of 8.9:1, why doesn't the IO-390 produce 220 hp?
Sorry for the thread drift, I too would like to see detonation data, and/or evidence of lack of detonation, on a IO-360-Axx with 94UL and 20 BTDC base timing.
 
I did not know that. It puzzles me why the combination of higher displacement AND the higher CR does not produce more power.

390/360 * 200= 216 even at the same CR.
With a CR of 8.9:1, why doesn't the IO-390 produce 220 hp?
Sorry for the thread drift, I too would like to see detonation data, and/or evidence of lack of detonation, on a IO-360-Axx with 94UL and 20 BTDC base timing.

Steve,

There could be several reasons for this that I can think of:

1. A number of sources (Monty Barrett, for one, when he was alive) state that the IO-360 is slightly over-rated and is more typically a 190-195 horsepower engine, while the -390 puts out an honest 210 hp.

2. Perhaps the stock angle valve heads become a little choked with the extra displacement.

3. It's possible that the tuning of the angle valve cold-air induction system is not quite optimal for the -390.

Skylor
 
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Indeed.

I don't even have problems when the fuel is heatsoaked on the ramp in 100+F temperatures, then takeoff and climb directly to those altitudes at max power. I know I'm levelling in the upper teens well before the hot fuel in the tanks has had a chance to fully cool down to local ambient, but I've never had a hiccup. I've done this with both 91E10 and 93E10, I'm running fuel rail pressure of 43-44 psig.

Now I'll say this - before I had the SDS system that keeps high fuel pressure all the way up to the injector face, back when I was still running a standard Bendix injection setup, then yes I did have a couple occassions that I could say were likely related to hot fuel vaporizing at high altitude in the climb, probably in the divider and spider lines to the injectors where the pressure was lower. After the servo I believe the pressure in a standard Bendix setup is about 6 psig, and after the divider close to zero. With SDS and EFII you get the full fuel rail pressure all the way to the injector face.

I've had my airplane up to FL210 on 91E10 without issues. Here is one screenshot from FL190 with a DA of 21000. Vapor pressure is not the issue.

At idle and a bit higher, the restriction is in the divider and post divider pressure is lower than pre divider. At higher RPMs, the resriction is in the injector and pressure is constant from the servo to the injector. I had thought the pressure was well above 10 psi at WOT, but not sure. Either way, it is way less than the pressures seen in EFII and therefore less tolerant of heat.
 
Either way, it is way less than the pressures seen in EFII and therefore less tolerant of heat.

Agreed. When I was still running Bendix injection I had already installed electric fuel pumps with a regulator. I changed my injector orifices to .024" and then eventually down to .022" in an effort to raise my idle pressure to a point where it would solve the "loping engine" associated with boiling fuel up front. The side-effect of this was that more pressure was required to move enough fuel at full-power conditions, and I ended up running about 38 psig to solve both problems acceptably. When I installed the SDS system I raised that a few pounds further to the current 43.
 
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very interesting and encouraging. Don't know what 702 is. Is that their 94UL or 100UL product? Guessing the latter, given the 104 MON rating, which should be in the neighborhood of 100 MON/RON.

Larry

702 is Swift's old tri-methyl-benzene formulation. Note that the report is 12 years old, and under their old corporate name Swift Enterprises, not the current Swift Fuels. Swift's current formulation is different in significant ways... but they're still aiming for a 100LL replacement, so 100 octane.

Paul
 
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