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Thread: Mogas/HP/Compression/Timing/Operating Cost

  1. #1
    Farmboy's Avatar
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    Mogas/HP/Compression/Timing/Operating Cost

    This topic has been beaten and rebeaten, but at the end of day, for me, the operating cost of avgas is largely unaffordable. Therefore I run mogas, and to date with small continentals and Lycomings it’s not been any issue at all.

    Years ago we tried to run mogas in my dads 180 Musketeer, and it did not like it I the summer at all. Went right back to 100LL.

    So I’m not interested in those that swear the carbs are junk after using mogas, or there’s all these other issues, as I’ve just not seen it. I am a believer in another opinionated issue, which is I use MMO in my mogas. Lubrication is something I believe in wholly.

    So in looking forward to a future airplane with a 180hp, I want/have to use mogas. If it were an off the shelf Titan 340, they offer it with low compression pistons making 170hp, to use mogas.

    But I happened across the following statement today, which piqued my curiosity.

    “......An alternative to running low compression pistons is to run a custom timing curve on electronic ignition. That's what I did. I run 90 octane(highest pump gas here) and have 2 maps. One for 100LL if I ever run it and want the bit of power back, and one for 90. The difference is 2 degrees retarded at WOT and 1 degree with the power back. It's a lot less HP loss than going to 8 or 7.5:1 pistons. And it's still a HP gain over stock at low power settings.
    But our parallel valve 540s were certified on 91/96 to begin with.....”

    So while he is using an o-540, the idea of using electronic ignition and different maps is something I had not heard of. We did it in bikes using power commander plug in boxes, but on an old tech aircraft engine?

    Along this vein is the information from another builder/pilot that after chasing airflow, baffles and vents he solved his high temp issues by simply dialing back his timing a few degrees. Seems he had set it a touch too aggressive based on mfg recommendations. Which makes me think there’s even more reason to have a modern ignition system.

    Anyone have solid info/data/experience with this?

    Thanks,
    Pb


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    PerryB's Avatar
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    All the little Lyc's/Cont's were designed to run on 80/87 so I don't see 90 Mogas being any kind of an issue (assuming no ethanol) with mags set to spec. They actually lose power and run slightly hotter on 100LL due to the slow burn of the high octane fuel. On my O-320/150 (using 100LL) I have actually bumped my timing up to 28 and it runs slightly cooler on both EGT and CHT, and makes a touch more static. 100LL wasn't the baseline fuel to begin with, so don't fret losing a few octane points. As Martha Stewart would say, "It's a good thing".

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    RVBottomly's Avatar
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    Watching for info too. I had pretty much committed myself to lower compression for the same reasons. But I was planning on using electronic ignition anyway.
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    aktango58's Avatar
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    What it the heck, are you NUTS?

    Keep the little bird. Bigger, badder, more power also comes with heavier, less fun to move around by yourself, more noise, costly and overall more effort.

    That said, some of the race sleds came out with timing adjustment you could set on the fly. EGT gets hot, change the timing and lower the power.

    But, the octane is not the end all be all- base metals!! Base metals are the lubrication and wear prevention to the valves. Avgas has much higher content of base metals than car gas, (Canada car gas has lots more base metals than we do fyi).

    For you flying around where you have a road and parts house within a few minutes walk and drive, the electronic ignition might be fine. For me, with little support and limited getting parts I am not excited about a system that can suddenly fail to start my plane, or not like being cold soaked.

    Would you run full engine monitor to keep an eye on your internal engine happenings?
    I don't know where you've been me lad, but I see you won first Prize!
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    Hmm . . . Been using 25% LL, 75% mogas for a while. Yields the same lead content as 80/87. Now auto and LL are within a few pennies of each other, so the only savings is spark plugs. $3.15 for car gas yesterday, tankful of 100LL at $3.49 last week. Only reason to use auto here is to reduce lead fouling.

    Re-setting ignition sounds like an experimental deal - I am locked in to a low advance by STC. I err on the high side, but am careful to not go out of bounds and void my airworthiness certificate.

    It has been a while, but isn't premium auto real close to 100 octane? I just use regular, and it is well above my minimum 73 octane.

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    Gordon Misch's Avatar
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    Premium no ethanol here is 91 octane. I use premium mogas with 8.5 pistons, per Peterson STC. I dont notice any performance difference compared to 100 LL
    Gordon

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    cubdriver2's Avatar
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    Love mogas, 23,000+ gallons so far. Plugs last 800 hrs. 8.6 compression. What's not to like?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    I've been running 90 oct mogas in a 8.5:1 O-200 with Pmags as well as an 8.5:1 160 HP O-320 in my SC clone for years now. Also running the same in my 160 HP O-320 in my RV. The only issues I've seen are clean spark plugs, cleaner oil and less valve guide wear. I don't consider any to be a problem. Often times the issue people see with Mogas have to do with vapor pressure and the engines wanting to vapor lock in hot conditions. That is typically caused by excessive heat at the gascolator or somewhere in the fuel system ahead of the carb and can be easily addressed by adding a cooling plenum over the gascolator and insulating (firesleeve) the fuel lines. The timing on both O-320s is per the Lyc book. The O-200 with Pmags runs an aggressive timing curve starting at 25° BTDC and ramping up to 39° BTDC at altitude. During the summer months I would switch to the less aggressive timing curve limiting the advance to 35° BTDC, primarily to keep the oil temps down since the O-200 didn't have an oil cooler. The 4° difference in timing advance typically made a 10° difference in oil temp during hot weather operations. It also made about a 20° difference in CHT.
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    PerryB's Avatar
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    I only have one complaint with Mogas, it doesn't SMELL like an airplane. Frankly it kinda stinks. I got my SES in a plane on Mogas, and a couple times while taxiing downwind it got rather rank in the cabin.
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    cubdriver2's Avatar
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    23,000+ gallons, savings? I could be flying 3 cubs instead of 2

    Glenn
    Last edited by cubdriver2; 01-16-2021 at 12:22 AM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    Quote Originally Posted by bob turner View Post
    Hmm . . . Been using 25% LL, 75% mogas for a while. Yields the same lead content as 80/87. Now auto and LL are within a few pennies of each other, so the only savings is spark plugs. $3.15 for car gas yesterday, tankful of 100LL at $3.49 last week.
    $2.64 for mogas here, $4.99 last time I bought 100LL. I’m still a bit cagey about filling my plane from fuel jugs in the winter due to the fear of static, but in summer the savings from using mogas are substantial.
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    cruiser's Avatar
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    The only benefit I have seen in going from an 0235 to an 0320 is the ability to purchase 2 gallons more per hour. I predict a painful cost increase in gas, soon. If the cost of 0235 cylinders was competitive I would have stayed with the 0235. MMO? Light oil, stoddard solvent, wintergreen oil for smell and red dye for color. Waste of money

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    skywagon8a's Avatar
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    Pb,
    Can you describe what your Dad's Mouseketeer did which indicated it didn't like the mogas? Was it the engine itself or was it perhaps vapor getting into the fuel lines? Do you suppose it was related to feeding from the low wing fuel tank? Perhaps if it was feeding from a high wing tank, it would have liked the mogas?

    The O-360-B, D series is a lower compression version rated at 168 hp. using 80/87 octane.
    My IO-360B1D is rated at 180 hp. The type certificate says 100 octane, yet the data plate is stamped 91 oct.

    There is a lot of good information here:
    Including this note: WHEN USING THE AUTOMOTIVE FUELS IDENTIFIED IN TABLE 2, LYCOMINGOIL ADDITIVE P/N LW-16702, OR AN EQUIVALENT FINISHED PRODUCT SUCHAS AEROSHELL 15W-50, MUST BE USED.

    Lycoming Service Instruction 1070AB SPECIFIED FUELS FOR SPARK-IGNITED GASOLINE AIRCRAFT ENGINE MODELS

    https://www.lycoming.com/sites/default/files/SI1070AB%20Specified%20Fuels.pdf

    I had R-680s in my Cessna T-50 which have a compression ratio of 7:1 and rated for 80/87 octane. When filling the tanks in Greenville, Folsom was out of avgas so was pumping something else which they would not tell me. I needed gas since they were using it, I used it. Climbing out of Moosehead I noticed a strange smell and a funny colored exhaust. But it ran OK. A little over an hour later when passing east of Boston over the water, both engines quit cold without warning. I pulled on the carb heat, because I couldn't think of what else to do. Then after what felt like a long time both engines came back to life with no more issues. Since they both did the same thing at the same time, it must have been something in the fuel lines feeding the engines. They both run from the same tank. The next day, I decided to burn off the Folsom gas and replace it with 100LL. While pushing the throttles up both engines sputtered and would not respond. When I slowly advanced the throttles they both gradually came up to full power and ran fine. Burned off the junk gas in one tank replaced it with avgas and then burned off the other tank, no more issues. I never learned what gas I was sold.
    N1PA
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    40m's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    23,000+ gallons, savings? I could be flying 3 cubs instead of 2

    Glenn
    I'de be happy if you just started flying the yellow one more often

    From Genesis: "And God promised men that good and obedient wives would be
    found in all corners of the earth."

    Then he made the earth round... and He laughed and laughed and laughed!

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    Dave Barras's Avatar
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    I was once told “if top lube is what you want, use 2-stroke oil in your gas, that’s what it is made for).
    Dave


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    Farmboy's Avatar
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    Quote Originally Posted by PerryB View Post
    I only have one complaint with Mogas, it doesn't SMELL like an airplane. Frankly it kinda stinks. I got my SES in a plane on Mogas, and a couple times while taxiing downwind it got rather rank in the cabin.
    It also doesn’t evaporate and stains worse. Just a compromise to use.


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    Current aircraft EI has variable timing based on manifold pressure but they lack knock sensors and a few other condition monitors that modern engine ECUs provide. Personally? For my own 10-1 engine that has injection and EI? I'm not interested in car gas. I can run LOP to save fuel dollars in cruise. That makes better sense than compromising on the fuel itself. To that topic the guys with EFI have an advantage in LOP ops.

    Adding oil to fuel displaces fuel by volume and subsequently leans your mixture. Make sure you have adequate fuel to do it. Especially when temps drop and mixtures lean as a factor of air density.
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  18. #18
    Farmboy's Avatar
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    Quote Originally Posted by Cub Builder View Post
    ..... The O-200 with Pmags runs an aggressive timing curve starting at 25° BTDC and ramping up to 39° BTDC at altitude. During the summer months I would switch to the less aggressive timing curve limiting the advance to 35° BTDC, primarily to keep the oil temps down since the O-200 didn't have an oil cooler. The 4° difference in timing advance typically made a 10° difference in oil temp during hot weather operations. It also made about a 20° difference in CHT.
    Good info thanks. 4 degrees timing for 20 degrees CHT must be what the other builder learned on his 180.


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    cubdriver2's Avatar
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    8a Pete, I forgot about my Stearman R680 time. Add 1700+ gal of 87 Oct from 6 gal cans that held 7gals. I fueled it by myself, long way up to top wing. And I always wonder why my shirt sleeves are always too short.

    Glenn
    Last edited by cubdriver2; 01-16-2021 at 10:09 AM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    Farmboy's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Pb,
    Can you describe what your Dad's Mouseketeer did which indicated it didn't like the mogas? Was it the engine itself or was it perhaps vapor getting into the fuel lines? Do you suppose it was related to feeding from the low wing fuel tank? Perhaps if it was feeding from a high wing tank, it would have liked the mogas?
    Pete very possible. I was too young/inexperienced to test/diagnose fuel flow or temp/vapor issues back then.

    Checked out fine on the ground, but about the crosswind turn on climbout it would drop to maybe 2000 rpm at wot and never give an hit more. Enough to keep flying back to land but I remember taking direct paths until I realized it wasn’t getting any worse.


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    cubdriver2's Avatar
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    Using MMO is by choice, I have never had a stuck valve. And those around me running it in little C engine haven't either. I picked up an old 3.5hp push mower last summer. The previous owner said it wouldn't start after it got hot. It started fine when it was cold but I shut it off and it wouldn't start hot. Exhaust valve hissing away. The correct thing to do is pull the head off and remove and clean the valves. But lazy me just dumped about a cup full of MMO in the little gas tank. After a few hours it starts fine hot or cold. It somehow magically fixed itself

    Glenn
    Last edited by cubdriver2; 01-16-2021 at 10:14 AM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    I used to run a mix in my R985. If I ran mogas alone, the throttle would get stiff (I think the seal in the accelerator pump would swell up). The mix would be OK. I actually got into the routine of only filling the center tank with mo gas, and the front and aft tank with 100LL. I used the front for take off and landings, the aft was kept full for ballast (flew much nicer aft loaded). If the airplane was going to sit more than a month, it would only have 100LL. Mogas goes bad quickly.


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    Utah-Jay's Avatar
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    Mogas has to be the future. The Price of oil has gone up about 15% in the past couple of months, so burning holes in the sky is gonna get more expensive.

    Currently avgas is $5.70, whereas I can get 91 octane for $2.45.

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    Mogas/HP/Compression/Timing/Operating Cost

    Perhaps another way to question fuel, electronics, and hp is simply, if you are starting with a -360 to build from scratch, what’s the best dollar input to get hp output on 91 octane?

    - fuel injection ?
    - port/polish/matched flows?
    - variable electronic timing?
    - heads/pistons/rods?

    Pb


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    cubdriver2's Avatar
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    The ignition system on newer snow machines automatically adjust to whatever fuel is put in it. Ex Cub should be able to do the same?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    cruiser's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    Using MMO is by choice, I have never had a stuck valve. And those around me running it in little C engine haven't either. I picked up an old 3.5hp push mower last summer. The previous owner said it wouldn't start after it got hot. It started fine when it was cold but I shut it off and it wouldn't start hot. Exhaust valve hissing away. The correct thing to do is pull the head off and remove and clean the valves. But lazy me just dumped about a cup full of MMO in the little gas tank. After a few hours it starts fine hot or cold. It somehow magically fixed itself

    Glenn
    A wise old fellow told me one time that if your gonna tell a bear story make sure there's lots of bears in it. This one needs more lawnmowers
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  27. #27

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    Avgas is 5.40 and mogas is 2.60 here. I burn a gas in my right tank and mogas in the left. Can’t tell any performance difference in the two where I do all my flying from 6,000’ and above. I bought the stc for mogas for my 160 hp O-320.


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  28. #28
    cubdriver2's Avatar
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    Quote Originally Posted by cruiser View Post
    A wise old fellow told me one time that if your gonna tell a bear story make sure there's lots of bears in it. This one needs more lawnmowers
    But I seem to remember you having a stuck valve on your Pa11?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  29. #29

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    Quote Originally Posted by Farmboy View Post
    Perhaps another way to question fuel, electronics, and hp is simply, if you are starting with a -360 to build from scratch, what’s the best dollar input to get hp output on 91 octane?

    - fuel injection ?
    - port/polish/matched flows?
    - variable electronic timing?
    - heads/pistons/rods?

    Pb


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    On my first cup of coffee but real cheap and quick HP can be had by using a prop that will let it turn 2700 on static run up Just keep an eye on the RPM one it comes off the ground. Several things can be done to add 5-10 HP each but they are not cumulative. So once you get that first 10 HP the rest will only give you a very small increase and little bang for the buck. If the compression is the same I believe the angle valve will make more power from the start. Fuel injection and variable electronic timing are great if you have a 5-7 thousand rpm range but I think you can make a stock system work fine in an O360. Vetterman small tube exhaust or hotrod. Spend some time on the carb venturi, superior sump. port/polish/matched flow, works according to Steve. So the question answer is which is best bang for that first 10 hp? I would say carb and exhaust because you are going to need them anyway. One thing not mentioned is a airboat cam.
    DENNY

  30. #30
    cruiser's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    But I seem to remember you having a stuck valve on your Pa11?

    Glenn
    Not that I recall. The lawnmower story was a good one although it needed more mowers
    Last edited by cruiser; 01-17-2021 at 02:30 PM.

  31. #31
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    Interesting discussion.

    An engine theory I have developed after racing sleds and watching folks hot rod lots of stuff: Your engine has a fixed amount of horses it will give you, once you have taken that out of it you need to rebuild or replace.

    Take an O-320 and hop it up, it will usually have a shorter life than one you don't. I am sure Peter has watched that with boat motors and guys trying to make a 350 into 700 hp!

    Cheap horsepower is exactly what Denny has figured out- remove air flow obstructions in and out, (including shaving gasket edges to prevent intrusion into the chambers), Increase accuracy of fuel flow to allow more accurate power balance, and get the gearing correct.

    Mousketeer: sounds like carb ice to me. I was WOT on a C-85 climbing out at 6,000 above mountains, running car gas, when she went silent with my father sitting next to me. Not good!

    As a cautionary tail, the new sleds are great performance engines, and lots of automatic gizmos to give more power, but a teaspoon of water and they burn down instantly! Also, it is much easier, and common, to tow the new sleds home than get your plane back to the hangar. My old school sleds are far more reliable, and I can put any gas avmaialbe and run it.

    MMO: Magic, smoke and mirrors? Lots of folks in all industries from Diesel engines to aircraft talk about engines with MMO history vs those without, and all say the MMO engines are much cleaner internally and show less wear. Stuck valves with MMO engines seem to be rare. If MMO removes or prevents carbon build up, that will help prevent stuck valves. $35,000 for an overhaul this year, after infrequent MMO use, has me convinced.

    Stewart, as always your observation on displacement of fuel by additive is on target! Thank you.
    I don't know where you've been me lad, but I see you won first Prize!

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    Quote Originally Posted by aktango58 View Post
    MMO: Magic, smoke and mirrors? Lots of folks in all industries from Diesel engines to aircraft talk about engines with MMO history vs those without, and all say the MMO engines are much cleaner internally and show less wear. Stuck valves with MMO engines seem to be rare. If MMO removes or prevents carbon build up, that will help prevent stuck valves. $35,000 for an overhaul this year, after infrequent MMO use, has me convinced.
    For those of you using MMO, how much are you adding per gallon of fuel?

  33. #33
    BC12D-4-85's Avatar
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    A shot glass full in 5 gallons seems to work ok

    Gary

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    4 oz per 10 gallons is what the instructions call for. I added a quart to every 100 gallons in my bulk tank for years. I stopped a few years ago. No difference that I can tell.

    An engine builder told me that the only use for MMO is to verify morning sickness. If a valve starts sticking at first start, add MMO to the oil. If it resolves the sticking? Get the valve repaired correctly.

    Increasing compression ratio adds approx 3-4% hp per full number up to 10-1 and then the gain drops off. Valve improvements about the same 3%. Fuel injection has varying increases depending on what you're comparing to what. Think about it. A Pponk 0-520 makes 265 hp. Add venturi valve seats? 275 hp. Add 8.5-1 over 7.5-1? 285 hp. With Cubs go from 7.5-1 to 8.5-1 in a 320? Add 10 hp. When talking about boats, snowmachines, cars, etc you're talking about engines spinning 6,000 to 10,000 rpm. Or state of the art car engines closer to 20,000 rpm. Very different from my airplane engines spinning 2,700.
    Last edited by stewartb; 01-17-2021 at 05:52 PM.

  35. #35
    cubdrvr's Avatar
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    In my spraying days I used auto fuel with 3 gal MMO in my 1000 gal tank running 235hp O-540's.........never an issue in 3000 hrs.....but auto fuel had a bit of lead in it then. I'm convinced that straight auto fuel today runs too dry......needs MMO or similar for upper cyl lubrication.
    "Sometimes a Cigar is just a Cigar"

  36. #36
    hotrod180's Avatar
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    Quote Originally Posted by cubdrvr View Post
    In my spraying days I used auto fuel with 3 gal MMO in my 1000 gal tank running 235hp O-540's.........never an issue in 3000 hrs.....but auto fuel had a bit of lead in it then. I'm convinced that straight auto fuel today runs too dry......needs MMO or similar for upper cyl lubrication.
    Or mix with 100LL.
    Cessna Skywagon-- accept no substitute!

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