Avgas in auto engine

[overtime]

My apologies if this topic has been covered before.

Does anyone have real data on which to offer insights on using avgas in an auto conversion? I am running a Subaru EA81 in a Karatoo-based aircraft and wonder what impact avgas will have on the Subaru when I start making longer flights and refuel at airports that do not have auto gasoline.

[FlyingRon]

If that engine still has the oxygen sensor, you're going to kill it in short order with leaded fuel.

[overtime]

No oxygen sensor on this one. I started with a basic core and built up the engine with Bing carbs, manifold, SS exhaust from Stratus. Core had incomplete ignition system so I installed a Crane Cams unit.

[Chris In Marshfield]

I'm a member of the FlySoob group on Yahoo!, and the topic has come up a fair amount pretty recently. I think that what people are seeing is that lead buildup on the valves keeps the system from sealing up tight (lower compression), as well as the potential for sticky valves. I believe that most try to use autofuel where they can, and judicious use of Decalin/TCP when avgas is the only option.

Here's a good thread to start with (presuming you can read posts in the group anonymously--I haven't tried):

http://groups.yahoo.com/group/FlySoob/message/10478

Best regards,
Chris

[overtime]

Thanks Chris. I appreciate the response and will definitely check out the link.

Terry

[Kiwi ZK-CKE]

Subs run really nice on Avgas - I run the EJ20 in my Adventurer on it. The only proviso as mentioned earlier is around Oxygen sensors. Mine doesn't have one and it runs really sweet. There is no way I would want to be stuck with auto fuel on this beast - lugging jerry cans around isn't my idea of fun.

[Chris In Marshfield]

Thanks for that bit of info, Kiwi. I agree jerry cans wouldn't be fun to have to carry around, especially in the plane that I'm building that carries at least 50 gallons of fuel!

How much time do you have on your EJ20 with avgas? Do you use any additives in the fuel?

I'm hoping that by the time I'm flying they'll have the unleaded avgas thing sorted out here in the U.S. Then I won't have to worry about it.

Best regards,
Chris

[Kiwi ZK-CKE]

I've got 50hrs on my EJ, but the guy who built my PRU has built several hundred EJ engines for Gyrocopters, most running on Avgas. They have collectively accumulated many thousands of hours with no issues related to Avgas use. Other than the O2 sensor, there is absolutely nothing in the engine that objects to Avgas. The car Rally guys here in NZ run Avgas in their WRX rally cars as it offers better performance.
An EA series engine will have even less problems - remember the EA81 was designed in the early 1970s, before unleaded fuel was widely available. Millions of running hours on high octane leaded fuel in the car fleet should give you some confidence. All you have to do is tune it with Avgas. Avgas is probably better for the older engines in many ways as its strict spec isn't subject to variations of performance additives and ethanol found in motor fuel, and which is known to cause problems. An interesting fact is the Subaru boxer engines were developed from an engine intended to power the Fuji FA200 light trainer aircraft built by the same company. I'm guessing the Sub designers were familiar with Avgas!....

[overtime]

Thanks for the response. This type of real-world information is exactly what I was seeking. I am impressed with the results of posting a simple question. I will not likely be needing to refuel with avgas within the next few weeks but it is reassuring to know that the EA81 should happily convert this fuel into enjoyable flying.

It would be really great if some photos of the engine installation on ZK-CKE could be made available. Having spent a great deal of time on my own installation, seeing how someone else did it could be quite instructive.

Terry

[Wilfred]

I had an oxygen sensor in my Lycoming O-320 exhaust pipe that 'fed' an amplifier; when it sensed OX it lit a light on instrument panel that indicated a need for mixture adjustment. That worked fine. I recall replacing the sensor twice in over 500 hours using avgas. Even when it began to fail it didn't die suddenly, but became somewhat irregular. I just used sensors from NAPA auto store.

[Kiwi ZK-CKE]

Here are some pics of my engine build to help with ideas. Be aware that the EJ series (I dont think the EJ20 was ever in a US Subaru, but the EJ22 was) is 2 generations newer than the EA81. Its an Overhead cam EFI 2 litre, whereas the EA81 has pushrods and a carb. EJs also come in two families, earlier single cam per side or the later twin cam models.

This is the starting point, straight out of a 1997 Legacy Brighton:

http://i2.photobucket.com/albums/y46/flyK1W1/IMG_0174-1.jpg

The core engine was completely stripped down and I had a mechanic friend overhaul it, with new rings, bearings etc and the heads were overhauled with seats cut and all that associated work. The bolts etc were all cadmium plated before they went back in.
I initially fitted the engine with a Real World Solutions (RWS) EFI control system with individual coils,but before it flew I changed this to a Link LEM4 controller produced here in NZ. I have nothing against the RWS, but was having trouble getting the engine to run and no-one locally knew anything about the RWS, and troubleshooting when there is no significant time zone overlap wasnt working. The Link is used in motorsport extensively here, and there are plenty of very knowlegable tuning experts who make it very easy to set up.
I am Running an Autoflight 2.4 - 1 reduction drive, also NZ made (manufactured just up the road from me) driving an Ivoprop in flight adjustable prop. I have modified the cooling mainfold to incorporate a filler cap, and I am using a small radiator supposedly off an Audi. The Radiator looks draggy, but in practice the airflow though it is very smooth, and unlike a lot of other Subaru conversions with lower profile or convoluted cooling arrangements, this runs at nice stable, cool temperatures no matter what. I have added an oil cooler to the front of the engine and a remote oil filter, running off an adaptor on the factory oil cooler mount. A very useful addition is a quick drain sump plug - this definitely is worth having as it makes oil changes very quick and clean.
I wanted to use lord engine mounts to isolate the engine from the airframe, so I made up 4 alloy mounts and had these machined. To work out what was required I first built up rough mockups out of wood so that I knew where to hang things in 3D space. The lower mounts are CNC machined from 6061 alloy block by Autoflight, and attach to the factory mount pads and new points on the gearbox casing. The lower mounts also hold the radiator. The top mounts are cast in alloy and machined, and these hold the Delco alternator (rather than the standard Subaru Denso - I wanted more electrical generating capacity). I used the wooden mock up mounts to make casting patterns (which is actually quite a lot of fun to do) and these were cast and machined for me by Autoflight as well.

http://i2.photobucket.com/albums/y46/flyK1W1/PA231942.jpg

Following are some photos of the powerplant during build - up, whilst it still has the RWS EFI with individual Chevy coils installed. When I went to the link this chaged back to the standard subaru coil pack with a Link ignitor assembly, so the wiring on top of the engine changed. I dont have any decent pics of its current config...

http://i2.photobucket.com/albums/y46/flyK1W1/eng24-11M-1.jpg

http://i2.photobucket.com/albums/y46/flyK1W1/eng24-11A-1.jpg

http://i2.photobucket.com/albums/y46/flyK1W1/eng24-11H-1.jpg




http://i2.photobucket.com/albums/y46/flyK1W1/IMG_7466.jpg

http://i2.photobucket.com/albums/y46/flyK1W1/eng26Aug3-1.jpg

The finished article installed in the Adventurer (Link fitted by this time)

http://i2.photobucket.com/albums/y46/flyK1W1/CKE-JK_0265small.jpg


I hope that gives some idea of what can be done anyway...

[overtime]

Well I certainly got more than I bargained for! Thanks for the pictures. Great job on the engine installation! Hope the Subaru gives you many more hours of enjoyable flying. My EA81 now has just over 70 hours and seems to be quite happy as an aircraft engine.

Terry

[martymayes]

Great pics and great project Kiwi!