What's new
Van's Air Force

The definitive Van's Aircraft support community! Buying, building or flying an RV? Join our exclusive family of mentors and enthusiasts!

IO-360-A1B6 and Mogas in cruise.

VH-VLY

VH-VLY

I'm New Here
Hello All from Australia

I have recently upgraded to a RV8 with an Lycoming IO-360-A1B6. I appreciate that this is a very complex issue, but does anyone have experience running 100LL in one tank for critical stages of flight and Mogas 93 AIK (equ to 98 RON in Australia, no ethanol) in the other tank for Cruise?

Thanks all.
 
Last edited:
Yes. T/O and landing in one tank (Avgas), cruise gas in another tank (Mogas/Clear Premium Non-ethanol). All hoses in engine compartment are insulated. Fuel pump has shroud with blast tube. That was when Avgas and Mogas had at least a couple dollar spread in price. Now, in WA state, with all the gas taxes being put on fuel, the price delta is about 50-75 cents, making it less attractive to go through the motions of having two fuels. I've seen Avgas at some airports be less than Clear Premium at the pump! In Idaho, clear premium is at a lot of town pumps and it's about 3.89/gallon while Avgas is about 5.50 to 6.00/gallon.
 
I had the same experience.
Stock A1B6D in my -7A.
It was in the mid 2000’s before ethanol was at every pump.
I never had any issues with auto gas in climbout, cruise, and descent. I always used the avgas tank for takeoff and landing.
In fact, over a hundred hours or so, I experimented with less than 100% in the in the Avgas tank. I was comfortable down to 50/50.
Worth noting: I’m at a 5000 msl airport. So I wasn’t making rated power. Also, my engine ran fairly cool.
 
Thanks for the tips and your experiences Aden and andoman.

My commute is about 3/4hr and Premium Mogas is quite a lot cheaper than 100LL in Australia, so makes sense for me if I can do it safely.

Do you know how your fuel systems are plumbed? Does the return fuel line go back to one tank? I need to study mine further.

Cheers.
 
I had no return line. Standard Vans FWF plumbing. I didn’t have any radius fittings into or out of the mechanical pump. I’m sure they were 90 elbows. Best practice would be to avoid those elbows. I did have fire sleeve on all the lines.
 
Only real issues is the vapor pressure is lower for mogas then 100. If you are going to run mogas on the ground I recommend a fuel return setup to help keep fuel temps below the boiling point.
 
lr172 said:
Only real issues is the vapor pressure is lower for mogas then 100. If you are going to run mogas on the ground I recommend a fuel return setup to help keep fuel temps below the boiling point.
Click to expand...
Hey Larry, do you have a link to recommended fuel return setup? I think I know what you mean, but I’m always learning.
 
VH-VLY said:
Do you know how your fuel systems are plumbed? Does the return fuel line go back to one tank? I need to study mine further.
Click to expand...
This is a very good idea. Gaps in understanding aircraft fuel systems have killed people. I recommend finding a reputable local RV builder/maintainer and ask them to spend a morning with you taking off the cowl, following the fuel lines and hoses, cleaning the filters, and generally ensuring that all is clear and understood. And then buy them a very nice lunch if they won't accept payment for this time.
 
akschu said:
Hey Larry, do you have a link to recommended fuel return setup? I think I know what you mean, but I’m always learning.
Click to expand...
I tap the top port on the servo. Its there to allow tapping for an FP sensor. It is sized for an ORB AN-4 fitting. This runs to my little manifold wherer the FP sensor is and I have another tap there for my return line. Run that to a valve that is rated for fuel exposure and can handle 50 PSI. I put this somewhere in the cabin. Then run a line from the valve back to an AN 4 bulkhead fitting in the tank. You can pull off the round access plate off the tank, intall the fitting and re install the plate.

This will rob enough fuel flow and pressure from your servo, so we need to limit the flow. Therefore you need to plumb in a limiter orifice. The pump can deliver around 45 GPH and you need around 15 or so for take off, so we want the flow somewhere around 10 - 15 GPH to be safe. You can find a calculator to determine size with Input PSI ( use 25), output PSI (use 1) and orifice size (the variable you adjust).

Because we have limited the flow, you will need to run the recirc for 20-30 seconds after a heat soak to get cool fuel in there. You can leave the valve open during ground ops to keep the fuel cool. Close the valve for take off. However, if you carefully designed the sysen, as above, leaving the valve open should not rob enough fuel to affect full power. Obviously higher flows will cool faster, but I don't like the idea of not flowing enough to the servo if you forget to close the valve, which I have done on more than one occasion (no impact).

CAUTION: Simply sharing my experiences and NOTTTTT recommending others do this. Any mistakes here can cause a loss of power on take off or other phases. modifications to the fuel system can cause serious issues.

AFP sell a pre packaged recirculation kit that is well designed and safe. It is installed near the spider and uses a cable to operate. It also recircs at the spider, so cools fuel further downstream, so better. However, I don't thimk that can be used with engine running. I am a fabricator at heart, so I made my own.
 
VH-VLY said:
Hello All from Australia

I have recently upgraded to a RV8 with an Lycoming IO-360-A1B6. I appreciate that this is a very complex issue, but does anyone have experience running 100LL in one tank for critical stages of flight and Mogas 93 AIK (equ to 98 RON in Australia, no ethanol) in the other tank for Cruise?

Thanks all.
Click to expand...
In my 14 I carry mogas in the left tank for the non critical stages of flight and mogas in the right tank for the critical ones
:)
YMMV, running unapproved fuels might cause death os serious injury
 
lr172 said:
I tap the top port on the servo. Its there to allow tapping for an FP sensor. It is sized for an ORB AN-4 fitting. This runs to my little manifold wherer the FP sensor is and I have another tap there for my return line. Run that to a valve that is rated for fuel exposure and can handle 50 PSI. I put this somewhere in the cabin. Then run a line from the valve back to an AN 4 bulkhead fitting in the tank. You can pull off the round access plate off the tank, intall the fitting and re install the plate.
Click to expand...
I’m not building an RV, so I stick to the FFW and avionics threads, but did something similar and wanted to confirm we were on the same sheet of music as I am also a fabricator.

I ran fuel lines from the forward and rearward ports of the high wing tanks, to a tee under the door, to a duplex valve, to the gascolator/sump, to the boost pump, to the shrouded/cooled engine driven pump, to a manifold, to the fuel servo, to a fuel flow sensor on top the engine, to the spider, to the cylinder.

The manifold has fuel pressure, fuel temp, and the very top port has a rivet crushed in it with a .020 hole in it going back to the duplex valve.

I learned this from VAF and think it should work, but not flying yet. My install requires that the fuel system gravity feeds to the pump fast enough to keep it flooded, otherwise it could suck air into the system if my tank unports.

Also, I need to test to make sure that the return fuel with both pumps running is significantly less than measured gravity flow to the pump at worst attitude and min fuel minus engine max consumption. I used 1/2 fuel lines so I think I’ll be okay.

Any thoughts on testing for vapor lock? I have a fuel temp sensor, but I can’t really see the low pressure area at the pump inlet. I could possibly pass the return line through a sight gauge on the wing root and observe for bubbles. Or perhaps I set some limit where mogas is off limits over a certain fuel temp.

Hopefully this isn’t too much thread drift, we are talking about running mogss in an injected kycoming.
 
akschu said:
Any thoughts on testing for vapor lock? I have a fuel temp sensor, but I can’t really see the low pressure area at the pump inlet. I could possibly pass the return line through a sight gauge on the wing root and observe for bubbles. Or perhaps I set some limit where mogas is off limits over a certain fuel temp.

Hopefully this isn’t too much thread drift, we are talking about running mogss in an injected kycoming.
Click to expand...
Assuming your boost pump is behind the FW, vapor lock should not be an issue in using the reurn setup. While you can get vapor at any time and anywhere, that is not vapor lock. Boiling fuel in the lines will cause vapor lock only if it exists before/upstream from the pump. Vapor downstream from the pump will only cause rough running due to the air creating inconsistency in fuel volume delivered. Vapor lock is when the pump sucks in too much air collected from the boiling full and fails to function, as it cannot effectively compress and deliver the air. With your boost pump in a cool environment, it will have no problems with vapor lock and the whole objective of the return system is to push those air bubbles back to the tank and replace with cooler fuel that will not boil.

I would not just use .020 restrictor because you read it on the internet. Find the flow rate formulas and do the calcs for your specific setup.
 
My O-360 Pitts was a 15 psi pressure carb with a rock steady mechanical gauge.

Above 7000' DA in a continuous climb, any large % of no ethanol mogas back in the MTBE days would cause a needle wiggle and later drops down to 8 PSI.

Levelling off fixed that, wait 5 minutes, then cruise climb to 10000 plus DA all was fine.

Today no ethanol winter blend vapor pressure is much less forgiving of heat and altitude, hence the common warm spring surprises if not careful.

Just a few data points from a RV6 carb'd guy that blends 50-50 100LL and Rec90 zero ethanol for cleaner oil and plugs in a 9:1 O-320. Except in spring.
 
Not a complex issue at all. Mine is an RV6A with an 0-360 A1A converted to SDS EM-5F fuel and electronic ignition and have been burning Costco Premium "with Ethanol" for the last 5 years and have had no problems. Take off or cruise, hot or cold. Ya when on the road I have to burn 100LL
Yes the system has return to tanks off the regulator.
I have a tank/pump transfer system in the back of my truck.
My luck varies FIXIT
 
lr172 said:
I would not just use .020 restrictor because you read it on the internet. Find the flow rate formulas and do the calcs for your specific setup.
Click to expand...
For sure, that’s what the math pointed to, but will confirm with testing.
 
Hey mate, not yet! Got busy with life, work, family and a cracking drought so not a lot of flying happening. Will let you know. How's things in Coota??
 
You are probably alright during all phases of flight, if you have lowered the advance timing from 25 degrees to 20 degrees, that Lycoming now advises for the angle valve
IO-360's.






s
 
Man, I read all these shenanigans y'all do running MOGAS in Lycoming engines not designed for it and all the pretzel contortions needed such as Spring mix, winter mix, ethanol, no ethanol, one tank Mogas, the other 100LL for T/O and landing, vapor locks, etc etc and it makes me wonder if the $1 or so per gal you're saving is worth it knowing you're rolling the dice with your plane and your life. Personally, I'll pay the extra $20 or so when I gas up knowing that the motor is happy and there are no worries or mental gymnastics needed to go fly today.

YMMV. Just saying.
 
Notso said:
Man, I read all these shenanigans y'all do running MOGAS in Lycoming engines not designed for it and all the pretzel contortions needed such as Spring mix, winter mix, ethanol, no ethanol, one tank Mogas, the other 100LL for T/O and landing, vapor locks, etc etc and it makes me wonder if the $1 or so per gal you're saving is worth it knowing you're rolling the dice with your plane and your life. Personally, I'll pay the extra $20 or so when I gas up knowing that the motor is happy and there are no worries or mental gymnastics needed to go fly today.
Click to expand...
It does seem complex and challenging at times, that's for sure.

I guess if you replace "mogas" with "experimental aircraft" you could see how someone would make the same argument - "why not just fly a certified aircraft? a bit more money, and much safer and no hassle with building something in your garage."

There are a lot of reasons people find to run unleaded fuel - save some money, better for the environment, enjoy experimenting and learning, convenience if airport doesn't have a fuel station, engine cleanliness, etc.

Different strokes. As I often say, if everyone thought exactly like I do, it would be a very boring world.
 
I read the current prices on any kind of RV model these days are in the 100's of thousands and guys are nickel and diming on mo gas verses avgas. If for no other reason, mo gas smells bad verses av gas smelling like Chanel #5 in comparison.
 
If one lives on an Airpark without Avgas on site, the ability to run pump gas raises the grin factor exponentially.
Even if Avgas is available, experiment safely and you will live happily ever enjoying more flying for the dollar. Yes, it’s only money. And opportunity cost is only cost…
 
There is a lot of learning and education that can go along with running mogas. The benefits of reducing the amount of lead is something I look forward to in the future when we get rid of it in avgas. I don't run it for similar reasons.....price difference...hauling, lifiting, dispensing, plus I don't have a good source of alcohol free mogas. But I understand the clap for those who do it.
 
You must log in or register to reply here.
Back
Top