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drmclaws

Member
I have a BPE IO-360 with a FP Sensenich. The compression ratio is 9:1. As with most of us the price of fuel is becoming a pain in the wallet. I was wondering if I could hear from those of you who are using 91 octane and those of you who have some knowledge regarding the pros and cons of its use. Many may not want to admit that they have gone that route but there are some real safety concerns I have such as vapor lock and damage to the engine. Lets assume we are not using blended fuels with alcohol. I mean there are many STC's out there for the use of MOGas and I used it with an STC on my 172 years ago. Can the lubricative (I don't know if thats a word) properties of lead be provided by some other means ie. Marvel Mystery Oil or are we doomed to 100 LL. What are the considerations when using an engine with higher compression ratios etc. I think this could be a real hot topic. One that has been around for years and which I'm sure is understood by some but not well comprehended by the rest of us.

Hope to hear from you.
 
What does the engine maker recommend?

Personally I am not going to experiment with 91 octane just to save a little.
 
drmclaws said:
I think this could be a real hot topic. One that has been around for years and which I'm sure is understood by some but not well comprehended by the rest of us..
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Uh...yeah - a hot topic for a long time! Try searchign the forums for "MOGAS", "Auto Gas", and similar search terms...then settle back for a few evening's reading....:D

Paul (currently paying almost the same for 100LL as for regular auto gas....):mad:
 
Price spread

Ironflight said:
Paul (currently paying almost the same for 100LL as for regular auto gas....):mad:
Click to expand...

Uh huh! At my current usage and calculating the spread between 100LL and 91 Octane Mogas, the cost difference is less than $30.00 a month. At the moment, I can't justify the hassle of mogas.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Here we go

1) Not one shred of evidence the lead provides any benefit whatsoever....A lot of tribal knowledge but no evidence. Think about it...Its an engine...As long as it has the hard valve seats lead free gas will be perfectly OK as it has been for every other engine for the last 30 years.

2) Detonation...This is a function of combustion temperature (CT) and ignition adavance (which really is related back to temperature). There is an argument that says that as the motor is air cooled the (CT) will be higher..and therefore any grade lower than 100 oct is cutting the detonation margin too fine... Well, in that case when Peterson Engineering did its extensive testing using specially blended 89 octane fuel it should have seen detonation...They found none!

Now all of the above holds true for 8.5:1 CR motors...You have 9:1...Will that make Much difference?..Probably not, and indeed there is more than one person running 87 octane in an 8.5:1 engine and they seem to be OK....But your situation is untested as far as I know.

3) Vapour lock...Probably the biggest argument against using mogas...In fact that is why my fuel pumps are in the wingroots..But there are many RV's running around with standard fuel systems and no VL issues...As a precaution you could run a tank of 100LL in really hot WX in one tank and 91 in the other. In my system there is no need to do this however.

Locally 100LL is a buck a gallon more than 91 octane (a local airport has just put a tank/pump of ETOH free in..Planes line up for miles..:)..).

Over 2000 hours the savings will roughly pay for the engine rebuild.

I been using mogas for 240hours (out of 270TT) without problem.

Frank
 
Oh yes

If you wanted to drop your CR to 8.5:1 i wonder how hard it would be to add a shim under the cylinders?...Should be easy to calculate the thickness (minus the thickness of the extra compressed gasket). You could probably do that on a Saturday morning you can borrow the tools.

Frank
 
Cylinder shims!

:eek:
frankh said:
If you wanted to drop your CR to 8.5:1 i wonder how hard it would be to add a shim under the cylinders?...Should be easy to calculate the thickness (minus the thickness of the extra compressed gasket). You could probably do that on a Saturday morning you can borrow the tools.

Frank
Click to expand...
:eek:

I personally would rather experiment with 91 mogas than with cylinder shims.
 
frankh said:
If you wanted to drop your CR to 8.5:1 i wonder how hard it would be to add a shim under the cylinders?...Should be easy to calculate the thickness (minus the thickness of the extra compressed gasket). You could probably do that on a Saturday morning you can borrow the tools.

Frank
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Sorry, can't easily change deck height due to pushrods (fixed length, thus valve clearance goes out of spec quickly). Usual method for CR change is to replace pistons, fairly easy to do...pull cylinders, replace pistons/rings, have cylinder honed and reassemble. Probably doable in 2 weeks with knowledgable mechanic plus some $$$.
 
probably faster

deene said:
Sorry, can't easily change deck height due to pushrods (fixed length, thus valve clearance goes out of spec quickly). Usual method for CR change is to replace pistons, fairly easy to do...pull cylinders, replace pistons/rings, have cylinder honed and reassemble. Probably doable in 2 weeks with knowledgable mechanic plus some $$$.
Click to expand...

Deene,
A good mechanic could do this in one (long) day. You can hone the cylinders easily on site.

Mark
 
For a thorough discussion by experts, go to EAA's website: http://www.aviationfuel.org/autogas/articles/

And, FWIF, Bart from Aerosport told me I could run premium with no problems.

Gas is blended for each market and the blends are changed throughout the year for changing weather conditions. In other words, the vapor pressure of mogas in Arizona in the summer is lower than it is in Oregon, and lower than it is in the winter anywhere.

Lastly, FWIW, I have flown mogas in my Cadet (with a Continental, and lower compression) since 1995 with no problems. All the guys at our airport with whom I have discussed gas used mogas until the state mandated ethanol.
 
I've used a 50 - 50 mixture of 100LL & 91 octane car gas for years. I've used it in 10.5 -1 piston engines to 6.75 - 1 engines. From RV-3a's to RV-10's. Never had a problem. The biggest problem with mogas is when the plane sits for an extended period of time. If you fly alot there will be little chance of varnish buildup. I've saved a ton of money doing this. Most of the time the difference is over $1.10 per gallon.
 
zilik said:
:eek::eek:

I personally would rather experiment with 91 mogas than with cylinder shims.
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20 years ago before high compression pistons were available, to increase compression it was common to surface grind the cylinder bases to bring the deck height down. I don't see how a shim shaped like the cylinder base could hurt a thing.

Also 87 pump gas works fine in a Lyc, I've been doing it now for over 700 hours.
 
Shims

rocketbob said:
20 years ago before high compression pistons were available, to increase compression it was common to surface grind the cylinder bases to bring the deck height down. I don't see how a shim shaped like the cylinder base could hurt a thing.

Also 87 pump gas works fine in a Lyc, I've been doing it now for over 700 hours.
Click to expand...

(Up on the soap box)

If you shim or grind the cylinder what happens to the pushrods etc?? I like the idea of experimental aircraft, but engines are what keep us out of the trees. On some engines, the bottom ring comes very close to the edge of the cylinder. You want to take a chance on a ring hanging?

Guess I value my butt (and my passenger's) too much to do other than approved engine mods or use approved fuel. For me, it's the same reason I personally wouldn't want to fly behind a car engine even though others might. Life's too short to experiment with stupid stuff.

I kind of think like Dirty Harry who said "A man's got to know his limitations". I'm not a powerplant engineer or structural engineer and know that. How many of you will modify the spar on your RV because you personally think it's OK?

It amazes me that the same people who are paranoid about primer and over-driven rivets would screw around with a perfectly good engine or take chances with the non-quality controlled crud for fuel that the A&P sells you so you can save a few bucks. Again, like Harry said "Well punk", "do you feel lucky?"

(Hopping down)

Don
 
Works for me...

I fly a Superior IO-360, 8.5/1 compression. The Superior engine manual specifically recommends 91 oct ethanol-free mogas. I don't think they would say this with no reason, so I have happily been using it for the past 6 months or so.

Unhappily, here in Oregon, the idiots at the legislature have dumped ethanol into our entire gasoline supply, hoping to keep the Ethanol lobby happy and $pending, while lowering fuel mileage for all oregonians. Oops! There I go ranting again, sorry...

Anyway, to test things, I did my normal cruise, 8500', full throttle, 2300 rpm, leaned 15 deg from peak, stabilized everything in smooth air. Then switched tanks from 100LL to 91 mogas waited a few minutes and... Nothing changed. Airspeed, MAP, CHT, EGT, no discernable diff at all.

I have always done takeoffs/landings on 100LL though, but to again test things, I switched tanks to mogas, slowed to just above stall in TO config then simulated takeoff. No hint of anything diff on climbeout from 1500' altitude. In the future I will test with actual takoffs, and expect no problems at all.

I expect the savings will help my insurance tab by at least 50%

Jerry
 
Oh come on Don

100LL is quality controlled?..Like there are how many engines that have been replaced by the oil companies because turbine fuel ended up in the 100LL tank..I guess if they pay for the engine its good as long as you survive..:)

Road fuel is QC'd as well...Just by the pure volume of it sold. otherwise there would be a LOT of cars stuck on the side of the highway...Personal anecdote but i have never heard of this happening to a car in 20 years.


i would argue the "crud" fuel argument is null and void.

Cylinder shims?..I dunno, I'd do it if Mahlon told me it was OK..:)
 
Hey Jerry

Jerry Cochran said:
I fly a Superior IO-360, 8.5/1 compression. The Superior engine manual specifically recommends 91 oct ethanol-free mogas. I don't think they would say this with no reason, so I have happily been using it for the past 6 months or so.

Unhappily, here in Oregon, the idiots at the legislature have dumped ethanol into our entire gasoline supply, hoping to keep the Ethanol lobby happy and $pending, while lowering fuel mileage for all oregonians. Oops! There I go ranting again, sorry...

Anyway, to test things, I did my normal cruise, 8500', full throttle, 2300 rpm, leaned 15 deg from peak, stabilized everything in smooth air. Then switched tanks from 100LL to 91 mogas waited a few minutes and... Nothing changed. Airspeed, MAP, CHT, EGT, no discernable diff at all.

I have always done takeoffs/landings on 100LL though, but to again test things, I switched tanks to mogas, slowed to just above stall in TO config then simulated takeoff. No hint of anything diff on climbeout from 1500' altitude. In the future I will test with actual takoffs, and expect no problems at all.

I expect the savings will help my insurance tab by at least 50%

Jerry
Click to expand...

Been using 91 mogas for 240 hours or so, run it lean of paek etc...My engine can't remember what 100LL is..:)..

Now we don't have to lug it to the airport in cans its a wonderful life...Especially if your an oil barron or ethanol farmer..Grrr!

Oh congrats on your CFI renewal!

Frank
 
Curious: Do you mogassers transport your own mogas to the airport, or is this available at some airports already? And when your xcountry, it's no big deal to switch to 100LL?
 
dhall_polo said:
Curious: Do you mogassers transport your own mogas to the airport, or is this available at some airports already? And when your xcountry, it's no big deal to switch to 100LL?
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I have a self contained 100 gallon tank (old aluminum diesel tank) a trailer with a 12V fuel pump & battery. Duel filters, fuel meter, and a 30' hose makes fueling any plane easy. Going CC I don't bother with mogas. Running 100LL though a system will help keep it clean. I fly about 250 hours a year so I use it quite often. So far I've pumped 4107 gallons though it, which is about $5,000 savings.

Just remember all you anti mogas guys, Rotax engines prefer 91 octane. If you are gonna build an RV-12 someday maybe you should look into it.
 
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Geico266 said:
Just remember all you anti mogas guys, Rotax engines prefer 91 octane. If you are gonna build an RV-12 someday maybe you should look into it.
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Just curious...does anybody know if an 8.5/1 compression Lycoming--or even a Rotax--will run OK on 91-octane ethanol-gasoline blends?
 
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I doubt that anyone is going to tell you it is ok to run blended fuel in your aircraft. I believe that most of the problem if not all of it is in the fuel components not being ethanol compatable. In other words some fuel lines or gaskets may swell or soften with ethanol blended fuel. I have never ran ethanol belended fuel in any aircraft engine, but like someone else said an engine is an engine. They were refering to mogas not ethanol. I have run 10% ethanol blended gas in everything from boats to heavy trucks and only one time have I had a bad reaction and that was with the fuel filter on a jetski. The ethanol swelled up the fuel filter to the point that it shut off the fuel. If that would have been an RV you would now have a glider. If I wanted to run ethanol in my Lycoming I would be sure that the fuel system was tolerant of ethanol I can't see what the engine would care.
As far as less fuel milage there would be a little less maybe not noticeable. I have heard reports of increased milage using a blend of 30% ethonal. I have not tried this.
By the way I raise corn and sell it to the ethonal plant down the road.
And I believe that the government should stop subsidizing ethonal.
 
AV Gas Blues

Rotax approves max 5% ethanol. I understand that their concern is not whether or not the engine will run ok with higher concentrations, but "washoff" of lubricating oil. The EAA has told me that Rotax is not happy with the gov't mandated 10%...of course, to this forum the concern is whether a Lycoming is sensitive to 10% ethanol "washoff"...the Rotax is a fussy little motor in some ways...I don't know, but do wonder.

Joe
 
rv on ethanol

wasn't there a group of RVs or other experimental class group at Oshkosh the other year flying on straight ethanol alone as a marketing strategy? They were all painted alike and trucked there fuel to the fly in. Does anyone know how they changed their fuel system?
 
Jerry Cochran said:
I have always done takeoffs/landings on 100LL though, but to again test things, I switched tanks to mogas, slowed to just above stall in TO config then simulated takeoff. No hint of anything diff on climbeout from 1500' altitude. In the future I will test with actual takoffs, and expect no problems at all.Jerry
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I ran MOGAS with no problems till one warm spring day I did a short hop and let the plane sit for 20-30 minutes and tried to take off again. Can you say "Hot Soak". Almost as soon as I got to full throttle, Vapor Lock! Good thing I had plenty runway. The fuel was probably still Winter Blend.

Bottom line is that the fuel system is the what needs to be designed for Mogas as I am convinced it will not hurt the engine, unless you are running a non-stock compression ratio then all bets are off.
 
I'm interested. I have a 6A with 10:1 an experimental BPE IO-360. I live in Payson AZ an airport elevation of Apx 5100 and gets pretty hot here in the summer with upper 90's and up to the mid 100's. We are able to get auto gas here consistenlty without alcohol. Question is why do you use a 1:1 blend?

Ivan McLaws
 
Your probably OK

drmclaws said:
I'm interested. I have a 6A with 10:1 an experimental BPE IO-360. I live in Payson AZ an airport elevation of Apx 5100 and gets pretty hot here in the summer with upper 90's and up to the mid 100's. We are able to get auto gas here consistenlty without alcohol. Question is why do you use a 1:1 blend?

Ivan McLaws
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But, remember the big risk with Mogas is vapour lock...This is most likely to happen as a result of a heat soaked engine and high altitude..I.e the mechanical fuel pump has been heated by the engine block and then is asked to suck on the fuel.

If you decide to go with moags..on a hot day where the engine has heat soaked, run the engine at high power for a half a minute to flush the fule thtu on the ground..If you have dump valve (like on the Airflow performance FI system) use it to flush the warmed fuel back to the tank.

An even sfae way would be to take off on 100LL and cruise on mogas..>At least until you know what conditions will lead to VL on your particular engine.

Alway run your boost pump in TO of course.

Frank
 
Yes I do have the Airflow performance FI system and the purge works great. Thanks for the info. So the problem is on a hot day with vapor lock. So assuming 91 octane and non ethanol gas is available do you think using 100LL in one and 91 octane in the other is viable as long as the days are not hot? As you say I might try AV gas in one tank and mogas in the other and see how it works. Again, my biggest concern was the 9:1 compression.

Still considering the bennefit vs. risk ratio.

Ivan McLaws
 
Been using Sunoco 93UL almost exclusively since flying.
I'm using a Superior IO-360, 8.5:1, which recommends a minimum of 91.
Have only used 100LL when UL unavailable enroute.

Big savings these days.
Glad I went with the 8.5:1.
 
Octane ratings of avgas and mogas are an apples and oranges thing--they aren't measured the same way. From Light Plane Maintenance, July 2000, as posted on EAA's website:
"The antiknock index posted on autogas pumps is approximately five points higher than the actual octane rating of aviation fuel?thus an antiknock index of 87 posted on an autogas pump would equate to about an ?average? 82-octane aviation fuel. Autogas STCs for 80-octane aviation engines require a minimum of 87- antiknock index."
 
100% EtOH

Just talke to someone from Vanguard Sqdr. They have an RV8 with a factory Lycoming IO-360 on 100% EtOH. The only change made was to have the servo recalibrated for the straight EtOH. No seal or o-ring changes made. The engine has 500-600hrs with no reported problems. FWIW
 
In regards to the lead requirement of the engine/valve seats: I was reading on the peterson site that the lead will remain on the seat for quite awhile after running 100ll. Their recommendation is that a tank of LL once in awhile is more than enough lead if it's needed at all. So even if you try to run mogas all the time the x-c fuel stops that only offer LL will likely meet any questionable lead requirements.

And to the naysayers who spout the "approved fuel" mantra; 91 oct autogas is approved by stc and extensive testing. Check with Peterson and the EAA site for your engine type.
 
So why can't we get 91 octane at the airport WITHOUT the dreaded alcy. I've been testing fuel at many locations here in Spokane, and I find the alcy in everything, even at those places that don't post having it. I think what would happen is what happened in the late 70 and early 80, we had a choice for unleaded gas and soon everything went to it. Those that need that extra, usually older stuff, they can stay with the ban wagon and have their own fuel dumps for that kind of fuel. I feel with the sport airplanes out there, using Rotax engines and all the other experimental engine, the demand for the 91 octane fuels are going to bring it to the airport, hopefully.
 
So is there anyone out there who has real world experience using 91 octane unleded fuel with no EDTOH on > 8.5:1 compression engines. I would be interested in knowing if you have had any problems with vapor lock, number of hours running etc.

Ivan McLaws
 
So is there anyone out there who has real world experience using 91 octane unleded fuel with no ETOH on > 8.5:1 compression engines. I would be interested in knowing if you have had any problems with vapor lock, number of hours running or any other helpful knowlege in this regards. I have a 9:1 IO-360 in my 6A.

Ivan McLaws
 
91 vs 100LL

I have a 0-360 with 8.5/1 pistons on my 6A and have been flying it for 2.5 years. I run 91 in my left tank and 100LL in my right tank. I use 100LL for take-off and landing and 91 for cruise. I will take-off and land on 91 after the first flight of the day and if the temps are less than 70 deg. (Just my comfort zone) I have not had any problems except the left tank started leaking fuel out a couple rivets and the right tank did not.

I can't say if it was the fuel or my sealing that caiued the leak so I don't want to get something started!!!! Fuel leaks are fixed and everyhing is back to normal.

Some people will run 91 and some 100LL, it's just what you feel comfortable with as PIC.....
 
From previous conversation

drmclaws said:
Yes I do have the Airflow performance FI system and the purge works great. Thanks for the info. So the problem is on a hot day with vapor lock. So assuming 91 octane and non ethanol gas is available do you think using 100LL in one and 91 octane in the other is viable as long as the days are not hot? As you say I might try AV gas in one tank and mogas in the other and see how it works. Again, my biggest concern was the 9:1 compression.

Still considering the bennefit vs. risk ratio.

Ivan McLaws
Click to expand...

We have at least one O360 driver that runs regular (87 octane) gas in his 8.5:1 CR motor...I would strongly suspect that 9.0:1 with 91 octane will be just fine..I just don't know for sure.

For really hot days and high altitude I would take off on 100LL..(in say the left tank)...91 in the right tank. This assumes you have a standard fuel system...I.e mechanical fuel pump. With your AFP purge valve this may not even be necessary as you can purge quite a bit of fuel that way....And as long as you run the boost pump you'll probably be OK even on 91 Mogas on hot days.


For me with electric fuel pumps only (wingroots) I only ever use 91 mogas, I would just advise caution due to your hot and high take off environment.

Frank
 
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