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Mogas vs. 100LL?

MOGAS any issues of mixture?

Dear fellows,
Recently I switched my 8's engine (Lycoming IO360-m1b) to operate on MOGAZ 96 Octane.
I met problems with the mixture adjustment: I had to move the Mixture lever a bit leaner while checking the engine prior to take-off end enrich more then usual for take-off and enroute flight.
I'd like to hear from you, if any one of you met this problem? And what is done for regular flights?
thanks
Ariel Arielly
8A 80295
 
Dear fellows,
Recently I switched my 8's engine (Lycoming IO360-m1b) to operate on MOGAZ 96 Octane.
I met problems with the mixture adjustment: I had to move the Mixture lever a bit leaner while checking the engine prior to take-off end enrich more then usual for take-off and enroute flight.
I'd like to hear from you, if any one of you met this problem? And what is done for regular flights?
thanks
Ariel Arielly
8A 80295

I do not see a problem. You run a little more rich. That's fine.

96UL? Never heard of that.
 
Dear fellows,
Recently I switched my 8's engine (Lycoming IO360-m1b) to operate on MOGAZ 96 Octane.
I met problems with the mixture adjustment: I had to move the Mixture lever a bit leaner while checking the engine prior to take-off end enrich more then usual for take-off and enroute flight.
I'd like to hear from you, if any one of you met this problem? And what is done for regular flights?
thanks
Ariel Arielly
8A 80295

Agree with TX

I lean the mixture on every runup, and where the mixture knob ends up to achieve the desired RPM rise is dependant on many variables including temperature, season, and DA. Same with target EGT on climb. As with most things on a Lycoming, the desired result from the engine is the target, not a rote physical location of the control knobs.

If you want near automatic engine response to throttle input, you need a properly programmed EFI system.
 
What is this world coming to, the price difference between 100 LL and regular car gas is $4 now x 8 g/h = $32 per hour.

Just passed 5,500 hours on my 6 since 1999. A lot of that on car gas. Love this plane like it is part of me. ;)
 
Depends on where you live. The price delta between the cheapest 100LL and the cheapest premium car gas is about 30 cents where I am. And if I want to go to a "brand name" car station like Chevron, car premium is more expensive than 100LL.

Just paid 5.71 for 100LL yesterday, and Premium grade at the local Chevron is still right around 6 bucks
 
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Depends on where you live. The price delta between the cheapest 100LL and the cheapest premium car gas is about 30 cents where I am. And if I want to go to a "brand name" car station like Chevron, car premium is more expensive than 100LL.

Just paid 5.71 for 100LL yesterday, and Premium grade at the local Chevron is still right around 6 bucks

This makes absolutely no economic sense.
 
After living in California for the last half century, I feel I'm qualified to opine that "reality" and "California" are now mutually exclusive terms.

I set the Rocket up to run car gas and frankly, there is virtually no economic incentive to do so today. 2 years ago when car gas was under 2 bucks, sure, but not today. Lets see what the prices do after November - then maybe I'll look at car gas again.
 
Summary
Even a relatively small amount of 100LL will have a significant impact on the vapor pressure of mogas. Ratios of one part 100LL to five parts mogas have proven satisfactory with both summer and winter blends across temperature ranges of 5ºF - 95ºF with an IO-360-B1B and the as-designed Van's RV-6/7 injected fuel system.

Detail
I've been running my -6A (IO-360-B1B) on premium no ethanol "mogas" from the Sinclair station down the street for roughly the last nine years / 1000 hours. My first step was getting schooled on the subject by Pete Howell, from whom I copied his vapor pressure test rig and sampled local providers of suitable mogas. There was, and continues to be, some variation between the local providers with respect to associated vapor pressure. The Sinclair station is best, followed closely by KwikTrip (midwest chain convenience store), and Holiday dead last. And the vapor pressures do change between summer and winter blends - the store managers are happy to tell me what they have and when they switch over in the spring and fall.

During the course of my initial testing, I sampled various ratios of the Sinclair stuff and 100LL; this has remained fairly consistent when I look at it each spring. And while the measured vapor pressures are *not* RVPs because they are done at a temperature other than 37.8ºC/100ºF, the relative vapor pressure as compared to straight 100LL is really what I'm interested in.

So with that, here's that chart again. Keeping in mind that without any 100LL, straight mogas tests between 14 and 16 in the summer about 12 in the winter on this scale.

29739183210_3f61ec300d_c.jpg


Based on this testing, I use a ratio of 1 gallon 100LL to 5 gallons mogas. This results in a significant cost savings. I've never had an issue with the engine stalling or quitting even while hot on the ground using this ratio. I've successfully used both the summer and winter blends as well with no issues provided there is not an opportunity for the fuel system FWF to get heat soaked. Even then, with the injected engine, it won't stall or quit but instead runs rough until the warm fuel in the system is replaced with cool fuel from the tanks.
 
Super Premium 93UL averages $3.89 here in Texas.
100LL is running closer to $5.

We have a boutique fuel in North Texas, year round, formulated for less vaporization. EPA mandated to stop polution.
 
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Locally, I have no Lycoming-approved alternative fuel options other than 100LL. These days, the FBO at the regional airport where I keep my plane gets $6.88/gal for 100LL. I buy it from them in a pinch, mainly when the convenience of them fueling in my hangar outweighs the price delta (currently $1.57/gallon) compared to the self-serve at a small rural airport about 15 flight-minutes away. I’ll get fuel there preferentially based on a variety of factors (quantity, time, convenience, amount etc). The price difference was more than that a few weeks ago…the delta has narrowed a bit recently. Not sure what that means, if anything.

My home airport is fueled by AvFuel, so I’m interested to see how the eventuality of G100UL affects the metric (i.e….how much and when). My guess…a lot more and not soon, be we’ll see.
 
Depends on where you live. The price delta between the cheapest 100LL and the cheapest premium car gas is about 30 cents where I am. And if I want to go to a "brand name" car station like Chevron, car premium is more expensive than 100LL.

Just paid 5.71 for 100LL yesterday, and Premium grade at the local Chevron is still right around 6 bucks

I just picked up 125 gallons of 93E10 at my local Walmart for $3.30 per gallon.
 
AutoGas

I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues? Has anyone tried those solutions in their experimental aircraft?

It is mathematically impossible to have a vapor lock issue if the fuel to the engine is pressurized! An engine "sucking" fuel is under a vaccuum, and WILL under certain conditions vapor lock, especially if there are 90* fittings in the hot engine compartment that allow cavitation of the fuel flow going into the engine fuel pump. These fittings need to be eliminated and replaced with curved hoses. Even a 5psi pressure FROM THE TANK to the engine fuel pump will eliminate the possibility of vapor lock! This is WHY the automotive industry put the fuel pumps INTO THE FUEL TANK!
AS Mike Bush has pointed out, detonation on MOST Lycoming engines (8.5:1) isn't an issue. Higher compression ratios need to be more carefull.
I've been running 93 oct E10 gas for the last 1000 hrs on my IO-360 8.5:1 compression engine with ZERO issues after implementing the above solutions. The engine now has 2065 Hrs on it, with zero valve issues (I'v NEVER had a sticky valve) and have NEVER had a detonation issue.
 
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I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues? Has anyone tried those solutions in their experimental aircraft?

It is mathematically impossible to have a vapor lock issue if the fuel to the engine is pressurized! An engine "sucking" fuel is under a vaccuum, and WILL under certain conditions vapor lock, especially if there are 90* fittings in the hot engine compartment that allow cavitation of the fuel flow going into the engine fuel pump. These fittings need to be eliminated and replaced with curved hoses. Even a 5psi pressure FROM THE TANK to the engine fuel pump will eliminate the possibility of vapor lock! This is WHY the automotive industry put the fuel pumps INTO THE FUEL TANK!
AS Mike Bush has pointed out, detonation on MOST Lycoming engines (8.5:1) isn't an issue. Higher compression ratios need to be more carefull.
I've been running 93 oct E10 gas for the last 1000 hrs on my IO-360 8.5:1 compression engine with ZERO issues after implementing the above solutions. The engine now has 2065 Hrs on it, with zero valve issues (I'v NEVER had a sticky valve) and have NEVER had a detonation issue.

Might have mentioned this before, but we burned 87UL in our C-172. Many hundreds of trouble free flight hours. At altitudes of 12,000 feet, in the summertime.
Vapor lock? Never.
 
... Has anyone tried those solutions in their experimental aircraft?

Yes. And thats why we can run auto gas.

Fuel pumps as low as possible relative to tank level...
No 90's on the suction side...
High pressure fuel rail...
Ethanol safe fuel components...
EFI...
Appropriate ignition curve...

It aint rocket surgery!
 
When EFI first came out in a widespread way (Bosch D Jetronic, in the late 1960s and L Jetronic in the mid '70s ), pumps were all external and that continued until about 1985.

Those pumps were mounted about level with the fuel tank bottoms in most cars. Worked fine, no vapor lock issues in most cases in engines with crossflow heads.

With attention to detail in the fuel system layout you can certainly use mogas in aircraft. Lots of folks are doing it successfully.
 
I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues?

As far as detonation issues, most modern cars have knock sensors, and retard the timing and/or enrichen the mixture at the first signs of knock (which is mild detonation). Older cars just did these things (retard timing/enrichen mixture) whenever you pushed the gas pedal all the way down, or the opposite, e.g., ‘vacuum advance’ which advanced the timing at low manifold pressures, retarded it at high MP.
 
MoGas

As far as detonation issues, most modern cars have knock sensors, and retard the timing and/or enrichen the mixture at the first signs of knock (which is mild detonation). Older cars just did these things (retard timing/enrichen mixture) whenever you pushed the gas pedal all the way down, or the opposite, e.g., ‘vacuum advance’ which advanced the timing at low manifold pressures, retarded it at high MP.

I also am running dual PMAGs with variable timing. At 20" manifold pressure & 2350 RPM, I see the engine timing at 33.6* (EI Commander readout). And I lean aggressively lean of peak. At 8000' I'm seeing 6.5 GPH at 2400 RPM.
 
Dear fellows,
Recently I switched my 8's engine (Lycoming IO360-m1b) to operate on MOGAZ 96 Octane.
I met problems with the mixture adjustment: I had to move the Mixture lever a bit leaner while checking the engine prior to take-off end enrich more then usual for take-off and enroute flight.
I'd like to hear from you, if any one of you met this problem? And what is done for regular flights?
thanks
Ariel Arielly
8A 80295

Ariel: same here. i run Avgas in one fuel tank and Mogas in the other. leaning the engine is a bit different with Mogas. i assume background is different speeds at which the fuels burn (moving flame front). it's just a bit different but you definitely don't have a problem in that regard.
 
Price of G100UL

The cost comparisons will be more apparent once we see 100LL disappear and replaced with G100UL. Best estimates are that this fuel will be about a dollar more than 100LL.
I am well aware that prices are all over the map across the US but here in CA 100LL has generally been about $2 more than 91E10 mogas.
Looking at a $3 difference might be an incentive for more pilots to experiment with 91E10 mogas.
 
As far as detonation issues, most modern cars have knock sensors, and retard the timing and/or enrichen the mixture at the first signs of knock (which is mild detonation). Older cars just did these things (retard timing/enrichen mixture) whenever you pushed the gas pedal all the way down, or the opposite, e.g., ‘vacuum advance’ which advanced the timing at low manifold pressures, retarded it at high MP.

Modern EFII still uses elaborate fuel delivery and ignition tables, based upon RPM, MAP, MAF, IAT, TP, etc. These are developed during countless hours on the Dyno. The Knock sensors are only relied upon for moderate changes and those changes usually start with ignition retard, and additional fuel is secondary, if used at all. The knock sensors are a key way for designers to get peak performance out of 93 octane fuel, yet still deal with 87 octane as well as severe conditions.

Larry
 
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I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues? Has anyone tried those solutions in their experimental aircraft?

.

As mentioned, they now run 40+ PSI all the way from the tank to the injector and that fully solves the vapor lock issue with all versions of modern auto gas. 20-30 years ago, when the pumps were under the car, poorly designed systems like some Chryslers, did suffer vapor lock issues.

Larry
 
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Vapor lock issues are all to do with pressure and temperature of a given fuel.

Given enough temperature, the volatile elements in the gasoline will still boil, even at 40 psi. The last generations of returnless port injection used pressures of around 60 psi to combat this after hot shutdown and heat soak since they could no longer pull the hot fuel out FWF as return type systems could. Think red hot turbos dissipating their heat under hood into the fuel rails and injectors.

In aircraft, we are generally more concerned about pressure at the pump inlet. Under high temperatures, it can take only slight suction there to cause mogas to boil. If severe enough, these bubbles won't collapse on the pressure side of the pump and the engine will lean out, run rough or even stop.

Bubbles are hard on the pumps too as they're not designed to pump vapor. The pump inlets should preferably be flooded or have minimal head and restriction to minimize this.

After evaluating returnless systems with the pumps in the tanks for aircraft, we decided to stick with return type systems using externally mounted pumps. This offer the advantages of purging hot fuel from from the block and regulator immediately on pump activation, easier servicing and permits all the fuel to be used from a tank if the pump fails.
 
The cost comparisons will be more apparent once we see 100LL disappear and replaced with G100UL. Best estimates are that this fuel will be about a dollar more than 100LL.

The authorities have stated that at the wholesale level, the added cost will be 80 cents to one dollar more.

We might be looking at $2 at retail levels.
 
I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues? Has anyone tried those solutions in their experimental aircraft?

Detonation is affected by several factors - compression, temperature, engine speed, and perhaps most importantly for us - cylinder size. Large bore, slow moving engines are more prone to detonation than smaller bore engines turning high rpm. We also have much higher combustion chamber temperatures with air-cooling than automotive engines using water jackets. There is not much we can do to prevent detonation in our engines beyond adjusting the timing and using good octane fuel, but that has already proven to be sufficient.

On the vapor pressure side, that has been solved as well - if people would just pay attention to the technology and do some research. The EFI solutions already in place for the experimental aircraft world (EFII and SDS chief among them) have completely resolved this issue, if you install them as intended. I've not had a single issue with vapor pressure since I installed my SDS package, and I run 93E10 in hot west Texas summers in the high teen altitudes quite regularly. Hot start problems are completely non-existent, it starts the same way everytime whether hot or cold, just like it should.

Our modern automotive vehicles don't suffer from these problems - why should our airplanes? Here in the EAB world, we don't have to.
 
I've been following this tread for a long time, even posted a couple of times. Everyone talks about autogas vapor levels and seasonal vapor level issues, as well as detonation issues. Can anyone tell me WHY this isn't an issue in the automotive domain? Has your car (with 10/1 compression levels) even experienced these problems? What have the automotive manufacturers done to elevate these issues? Has anyone tried those solutions in their experimental aircraft?

It is mathematically impossible to have a vapor lock issue if the fuel to the engine is pressurized! An engine "sucking" fuel is under a vaccuum, and WILL under certain conditions vapor lock, especially if there are 90* fittings in the hot engine compartment that allow cavitation of the fuel flow going into the engine fuel pump. These fittings need to be eliminated and replaced with curved hoses. Even a 5psi pressure FROM THE TANK to the engine fuel pump will eliminate the possibility of vapor lock! This is WHY the automotive industry put the fuel pumps INTO THE FUEL TANK!
AS Mike Bush has pointed out, detonation on MOST Lycoming engines (8.5:1) isn't an issue. Higher compression ratios need to be more carefull.
I've been running 93 oct E10 gas for the last 1000 hrs on my IO-360 8.5:1 compression engine with ZERO issues after implementing the above solutions. The engine now has 2065 Hrs on it, with zero valve issues (I'v NEVER had a sticky valve) and have NEVER had a detonation issue.

While my aircraft is not a low-wing aircraft, I have been experiencing significant vapor lock conditions with the O360-A1F6 engine. This engine had a mechanical fuel pump installed.

I have modified the fuel system to remove the engine-driven fuel pump. I now have gravity feed (yes, I'm a high wing aircraft) supplemented by a simple Facet electric pump mounted in the cockpit tunnel.

Initially I blamed fuel quality for my vapor lock woes - I was running 91 octane ethanol-free mogas. Then I switched to 100% 100LL. On a day when multiple quick turn-arounds were performed (Young Eagles event) I experienced vapor lock at engine start-up each and every time, without fail.

Fast forward a few weeks. Engine-driven fuel pump was removed and a blanking plate installed. Approximately 18" of fuel line was removed from the fuel delivery system forward of the firewall. Several test flights were performed, starting with 100% 100LL and varying down to 100% 91 octane ethanol-free mogas.

The next big test was another Young Eagles event. My previous testing had produced such encouraging results that I ran 100% 91 octane mogas for the Young Eagles event, complete with all its quick turn-arounds and all this on a day that was 4degC warmer than the previous Young Eagle event.

The engine experienced exactly zero vapor lock events. Zero.

While this sample size is statistically irrelevant, I have to believe the source of my on-going vapor lock issues was the heat-soaking of the fuel, particularly within the mechanical fuel pump and its associated vertically-oriented fuel lines. I'm so very glad to get rid of this vapor lock challenge in my aircraft.

For those who might have the option of removing their engine-driven fuel pump (perhaps if the electrical system supports it, by installing a backup electric fuel pump), this may prove a means of reducing the risks of vapor lock.
 
Or, when you replaced the fuel lines you fixed a fuel line air leak. My experience is such leaks allowing air in have symptoms similar to vapor lock. The offending air leak was on the mechanical fuel pump (non Lycoming engine).

Carl
 
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….I have to believe the source of my on-going vapor lock issues was the heat-soaking of the fuel, particularly within the mechanical fuel pump and its associated vertically-oriented fuel lines. I'm so very glad to get rid of this vapor lock challenge in my aircraft.

For those who might have the option of removing their engine-driven fuel pump (perhaps if the electrical system supports it, by installing a backup electric fuel pump), this may prove a means of reducing the risks of vapor lock.

On my IO-320 with the usual engine-driven pump and a Weldon boost pump located on the firewall, and using exclusively 100LL, I don’t ever get actual vapor lock (fuel injected) but when hot and on quick turn-arounds, I do get fuel pressure variability (low) on the gauge while taxiing, as well as moderately hard starting. No problem in the air. I assume that it’s just too darn hot under there. I’m addressing it with fuel line insulation and additional exhaust shielding, and for short-term parking on the ramp I also made a muffin fan on a 1 hour timer that I put over the oil door on the cowl to exhaust the engine compartment after parking. I haven’t flown these fixes yet and won’t get a chance until mid-October. Certainly by that time ambient temps will be cool/cold, so I may have to wait until next summer to evaluate.
 
Wow. Just wow.

Impossible is a dangerous term. Guess all that thermo work involving pressure versus temperature tables was a waste of time.

When someone operates their car at 20k feet, please post about the experience. If we want to stick with anecdote, look at the difficulties the somewhat older cars have in the high Rockies; over-rich roughness, poor sometimes no starting, and yes, vapor lock on some summer days. That’s only +\- 10K elevation.

I’ve stated here before, if designs where only bounded by a single set of conditions then most anyone could be a system designer.
 
Wow. Just wow.

Impossible is a dangerous term. Guess all that thermo work involving pressure versus temperature tables was a waste of time.

When someone operates their car at 20k feet, please post about the experience. If we want to stick with anecdote, look at the difficulties the somewhat older cars have in the high Rockies; over-rich roughness, poor sometimes no starting, and yes, vapor lock on some summer days. That’s only +\- 10K elevation.

I’ve stated here before, if designs where only bounded by a single set of conditions then most anyone could be a system designer.

The key takeaway here is…somewhat older cars.
Any modern state of the art engine will not have problems, provided the plumbing is done correctly.
 
Wow. Just wow.

Impossible is a dangerous term. Guess all that thermo work involving pressure versus temperature tables was a waste of time.

When someone operates their car at 20k feet, please post about the experience. If we want to stick with anecdote, look at the difficulties the somewhat older cars have in the high Rockies; over-rich roughness, poor sometimes no starting, and yes, vapor lock on some summer days. That’s only +\- 10K elevation.

I’ve stated here before, if designs where only bounded by a single set of conditions then most anyone could be a system designer.

Not sure what you mean by older. Any EFI car built in the last 30-40 years will go to the top of Pikes Peak and run just fine. Carb car maybe not. Few people here are flying at 20K but Greg has flown at 21K DA with mogas on a hot day.

I have dozens of customers flying auto engines at 10-18K feet with EFI on mogas, works just fine.



greg.png
 
Not sure what you mean by older. Any EFI car built in the last 30-40 years will go to the top of Pikes Peak and run just fine. Carb car maybe not. Few people here are flying at 20K but Greg has flown at 21K DA with mogas on a hot day.

I have dozens of customers flying auto engines at 10-18K feet with EFI on mogas, works just fine.

My problem is the "It is mathematically impossible to have a vapor lock issue if the fuel to the engine is pressurized!" Practically? for our purposes with even a little local environment consideration = yes. If there's a fuel that has a perfectly flat line on the phase diagram, I've never seen it.

We have property in Summit County, CO with a base of ~9700 ft. We're out there a lot. Within the last 7-8 years in rental cars; I've been in a Jeep that chugged violently going over Independence Pass, a Mitsubishi that wouldn't start after a hot shut down (raising the hood and letting the fuel pump run sped things up), another hot restart problem car that I can't remember the details. Sure, I don't know how these cars had been treated but they were new enough that they had probably only had routine maintenance performed.

I'm a big proponent for some auto applications, configuring fuel systems for fuel flexibility, etc. The anecdote often stated here can get worrisome at times.

Side note. Your Pikes Peak reference is a much better example of modern braking advancement; e.g. tourist that don't understand or practice compression braking.

Man, it's only Monday and a hurricane is on the way. Enjoy your work week.
 
I see we are back to EI, which is related I guess to G100UL. I know GAMI has worked on this for years. I know the blend is not new or earth shaking, UL fuel, gasoline has been around for a long time. Rhe trick is getting to well over 100 Octane.

I like to see wide spread (all over USA) trials in GA community, BEFORE, going all in.

Besides cost what is the lubrication or lubricity of the new fuel. Will we see long term wear issues of values? No offense to FAA or GAMI. Just because the Feds approved it does not mean it's golden.
 
The GDI rentals with some miles and no port injectors will run horrid. Just had it in the NE US. No check engine light, light knock, multiple refills.
 
We have property in Summit County, CO with a base of ~9700 ft. We're out there a lot. Within the last 7-8 years in rental cars; I've been in a Jeep that chugged violently going over Independence Pass, a Mitsubishi that wouldn't start after a hot shut down (raising the hood and letting the fuel pump run sped things up), another hot restart problem car that I can't remember the details. Sure, I don't know how these cars had been treated but they were new enough that they had probably only had routine maintenance performed.

I'm a big proponent for some auto applications, configuring fuel systems for fuel flexibility, etc. The anecdote often stated here can get worrisome at times.

Direct injection without also having port injection, has additional issues that port injection alone doesn't have due to the engine mounted, ultra high pressure, mechanical pumps and injectors spraying into the combustion chamber. That doesn't apply to this discussion though as most engines we fly here are carbed or have port injection.

What I'm saying is- we know what to do here to make mogas work and collectively have tens of thousands of reliable flight hours on aircraft in summer heat conditions. Follow the same recipe and cautions and you'll get the same results.

Yup, using winter mogas in a Rotax 912 or a carbed Lyc on a summer day and you'll almost certainly have vapor lock issues as many have. Do some other unwise things in the fuel system, ditto.

Nobody is defying physics here. We're staying inside the safety zone.

I posted Greg's photo because we have lots of skeptics here. Greg lives in TX- not exactly known as a cool state. This shows a worst case scenario. Mike also has lots of hours flying his Rocket on mogas in severe heat around Mojave.
 
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I posted Greg's photo because we have lots of skeptics here. Greg lives in TX- not exactly known as a cool state. This shows a worst case scenario. Mike also has lots of hours flying his Rocket on mogas in severe heat around Mojave.

Correct - I can take off with 104-106 F ground temps and sun-soaked wing tanks, and do a max performance climb into the upper teens without exceeding 400CHT or experiencing vapor lock.

It CAN be done.
 
Or, when you replaced the fuel lines you fixed a fuel line air leak. My experience is such leaks allowing air in have symptoms similar to vapor lock. The offending air leak was on the mechanical fuel pump (non Lycoming engine).

Carl

Carl - thanks for this thought. I suspect air leakage to be improbable in this case but I can assure you that removing the mechanical fuel pump DID fix a long-standing oil leak from its crappy mounting gasket, a fact for which I'm quite thankful as it was the only oil leak on the engine. :D

EDIT: Why do I suspect air leakage to be improbable? Simply because I would see high fuel pressure after a short ground turn-around - this would be indicative of a fuel system actually holding air rather than leaking air, and fuel heating, vaporizing and expanding to cause an increase in fuel pressure in a sealed system. Maybe I'm all wrong on this but that's the direction the evidence led me. Keep in mind this is a carb'd engine, so fuel pressure from gravity feed alone is very little thus the 8-9PSI that I frequently saw before cranking the engine was abnormally high pressure.
 
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Direct injection without also having port injection, stuff has additional issues that port injection alone doesn't have due to the engine mounted, ultra high pressure, mechanical pumps and injectors spraying into the combustion chamber. That doesn't apply to this discussion though as most engines we fly here are carbed or have port injection.

What I'm saying is- we know what to do here to make mogas work and collectively have tens of thousands of reliable flight hours on aircraft in summer heat conditions. Follow the same recipe and cautions and you'll get the same results.

Yup, using winter mogas in a Rotax 912 or a carbed Lyc on a summer day and you'll almost certainly have vapor lock issues as many have. Do some other unwise things in the fuel system, ditto.

Nobody is defying physics here. We're staying inside the safety zone.

I posted Greg's photo because we have lots of skeptics here. Greg lives in TX- not exactly known as a cool state. This shows a worst case scenario. Mike also has lots of hours flying his Rocket on mogas in severe heat around Mojave.

Never my point but guess I wasn’t clear. I’m also configuring my aircraft for mogas usage. I will test the suction system and pressure under 2 pump flow, half of the pick-up blocked off, half of the pre filter blocked, side with the highest frictional loss (flop tube), let the fuel warm, etc. Once I know the margin between actual and theoretic, I’ll push the temperature until I start seeing phase change.

I’ll state again my issue was with the statement "It is mathematically impossible to have a vapor lock issue if the fuel to the engine is pressurized!". Temperature affects the fuel properties. Pumps are delta P devices controlled by delta P devices (not absolute). Broad statements and non-quantified experience that declares there is no edge of the cliff is dangerous. Words matter.
 
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Broad statements and non-quantified experience that declares there is no edge of the cliff is dangerous. Words matter.

In my world, validation by doing something repeatedly (shall we say thousands of times in this case) gives us good confidence that we have arrived at a sound and safe solution. Seems we are all qualified to experiment and establish our own safe limits based on that experience, knowing the potential dangers.
 
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from what my experts say, this is not required; it may be an old wives tale. JMHO.

Yes, old wives tale. Very old.

The doom and gloom of the switch to unleaded fuel eating valves in cars never happened on the large scale we were told was going to happen. Yes I am old enough that I never saw the problem of vehicles eating valves and developing upper cylinder wear when lead was removed from auto fuel. Yes I was driving cars when all auto gas had lead in it and was driving the same car when the switch to unleaded gas occured. I had four uncles in the auto repair and gas station businesses. My uncles did not get more work when the switch to unleaded fuel occurred.

Others talk about the wonders of Marvel Mystery Oil (MMO) being added to their fuel. IMHO, those that are worried about lead being removed from our AvGas can find a solution for the problem by adding MMO to their unleaded AvGas.

Please pass the pop corn as this thread is going to get interesting.

Using Duck Duck Go to search the internet, (people can say anything on the internet and do) one will find both articles saying removing lead from fuel will cause wear and articles saying removing lead has more benefits than short comings. I just want to see the RAW data and draw my own conclusion.
 
......Yes I am old enough that I never saw the problem of vehicles eating valves and .....

Ha! I'm old enough to remember that too, and I did indeed have serious valve seat recession in my 1966 GTO engine. It ran fine until a hydraulic lifter bottomed out and that cylinder started misfiring. Most exhaust valves were recessed about 0.05, but that one troublemaker recessed about 0.150!

After 1971, GM and pretty much all others started hardening the exhaust seats which fixed that problem.

What's that got to do with Lycomings? Absolutely nothing. They already have hardened exhaust seats (at least any of the ones we typically use today).
 
Best practice for those considering EFI and mogas use in RVs:

Pump placement should be on the floor, not FWF

No drilled 90 deg fittings prior to the pumps, mandrel bent 90s are acceptable

90s are ok downstream of the pumps

-6 line for all plumbing

Return fuel from the regulator should go back to the tanks, never back to pump inlet

Never use winter gas in the summer. Drain out that old fuel if in doubt

Good idea to buy a Peterson/ Hodges Fuel Volatility Tester, especially as the seasonal changes in fuel formulations occur in winter/ spring/ summer
 
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Best practice for those considering EFI and mogas use in RVs:

Pump placement should be on the floor

No drilled 90 deg fittings prior to the pumps, mandrel bent 90s are acceptable

90s are ok downstream of the pumps

-6 line for all plumbing

Return fuel from the regulator should go back to the tanks, never back to pump inlet

Never use winter gas in the summer. Drain out that old fuel if in doubt

Good idea to buy a Peterson/ Hodges Fuel Volatility Tester, especially as the seasonal changes in fuel formulations occur in winter/ spring/ summer

Good advice!
For those in the North Texas area (DFW - Dallas - Ft. Worth), we have the same fuel year round. A special blend to reduce vaporization. The RVP is close to that of 100LL.
 
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