What happened to the Subaru Aircraft Engine?

It is an interesting question. I invested no less than ten years towards the conversion of Subaru engines for aircraft use and have followed the movement closely for about fifteen years. In my opinion, I was successful – more on this later.  Why are we not seeing Subaru Aircraft Engines at fly-ins and magazines?  Where have they gone?  Why are there not several companies offering their own conversion packages and making gobs of money while pulling aviation into the modern era with better, cleaner, more efficient, less expensive engines?

In my opinion… hey!  This my blog – I don’t have to say that do I?!?!  There are a bunch of factors at work.

There is no evangelist for Subaru Aircraft Engines or the conversions of them. Nobody is standing up and preaching to the masses about the benefits of the Subaru engine.  There have been a few that some would label as such (but I disagree). Jan Eggenfellner comes to mind. He was a stake holder and evangelist. He drove the Subaru conversion world, he marketed, he preached, he convinced people.  Sadly, he didn’t test, validate, or evolve his products – he simply walked away with hundreds of “believers” holding ten of thousands of dollars of “junk” (arguably) when he realized what a huge mess he had created and that fixing it would take a massive pile of money. He did aviation and specifically the Subaru world a terrible disservice.  He was not the first nor will he be the last.  His former customers have been unbelievably kind in not tearing him apart in court and in the press – amazing to me. To those that are “Viking Aircraft Engine” customers – don’t start crying when the same thing happens to you.  There is plenty of history there for you to have made a better and different choice.  I guess the saying is true: “We learn from experience that man does not learn from experience.”

Subaru Aircraft Engine EJ-22 EJ-25 SoobVery few people want to actually “construct” something in the sense necessary to convert an auto engine for use on an aircraft. Many like to assemble parts assuming it requires as little thinking and labor as possible.  Look at the numbers of people “constructing” a Van’s RV versus the number currently constructing Long-EZ’s or similar. Is a Long-EZ a “poor” airplane? Of course not. It simply requires a great deal of work to construct (compared to an RV).  The amount of “construction” (design, effort, head scratching, build a prototype part, throw it away, build another, etc…) that is required when creating an automotive engine conversion is massive when compared to what is required to bolt on an firewall forward package.  It is worth noting that I have nothing against RV’s – I fly one and love it. I believe the success of Van’s has been good for all of experimental aviation (sport aviation, if you must).

Very few people want to spend big bucks on something “experimental.”  Buying a Lycoming, Continental, or Rotax (912-style) is a relatively known quantity. You may be forking out $25,000 – $50,000 but you know what you are getting and know that it works because of their documented track record.  Thanks to businessmen such as those mentioned above and the non-existent track record of any “new” package – laying out this kind of cash is pretty tough for most everyone. Anyone that has been around experimental aviation for any length of time has seen the snake oil salesmen come and go taking the money of the young, unsuspecting, gullible, hopeful, and/or stupid with them.

With any unknown, getting insurance for it can be rather difficult and/or expensive.  Some folks don’t care about this. Some do.  I’ve personally watched ten years of hard labor burn to the ground in front of the builders eyes in a matter of five minutes – no insurance – a total loss – nothing but pictures to show for the many, many hours and thousands of dollars.  No, a check does not replace the blood, sweat, and tears but it does help.

The emphasis of most general aviation aircraft is on lightness.  A “properly” converted Soob is not light.  It may not be any heavier than a Lycoming or Continental but that should not be confused with light.

The Subaru presents a couple of challenges that are very difficult, if not impossible, for a small company to overcome.

  • It is a small displacement, high revving engine so it requires a Propeller Speed Reduction Unit (PSRU, gearbox, reduction drive, etc…). This requires engineering, precision manufacturing, loads of hours to prove in the test cell, and then many hours/years of flight time to create a track record that customers believe and can trust.  To date, those who have tried have failed.  There are a few PSRU manufacturers around but not many and finding people with thousands of hours behind the units is very near rare/difficult.  If you do find one, find out how much he has had to work on/modify the PSRU – I’ll bet it’s a lot.
  • The uneducated believe that the automotive fuel injection and ignition control will work in an aircraft.  This is a nice thought but proven to be wrong. With the early units, it was possible.  Time has proven that this is a bad plan and current EFI systems are becoming more and more complex making them less and less appropriate for aviation use. However; there are a couple of very good aftermarket EFI units available.   Some believe that strapping a carburetor on is the “smart” approach.  If running normally aspirated and one doesn’t care about any of the advantages of EFI, a carb works. It is far from a good solution though if one is trying to truly take advantage of all that a Subaru engine offers. Ya, people fight about this all the time – people once that horses were superior to automobiles for transportation. For those in this camp; get over it and join the modern era – do some research and try to learn something.
  • The more recent engines are adding much complexity that is simply not desired  in an aircraft engine. Variable valve timing is an example. Eliminating these types of things is no simple task and may (probably) significantly alter the highly reliable nature of the engine.
  • It is well understood that one can get these engines to produce a great deal of torque and/or work well for us at altitude with a turbocharger.  Yes, indeed.  However; most people do not understand how to properly size a turbocharger for aircraft use nor do they understand that an intercooler is mandatory or that electronic fuel injection and timing control is also required for reliability.  Once you get past all that, you must have an in-flight adjustable propeller to properly use the power that is now available to you at altitude.  Guess how much all of this cost you? Not just in terms of dollars but also complexity, reliability, weight, and maintenance.

Why are there no companies offering Subaru Aircraft Engines and conversion kits?  Because no market exists. Without a market they cannot sell enough products to make money. Without money they cannot stay in business.  Yes, this makes me sad but it is the free enterprise system that I support and defend even though it is largely lost at this point.

So, we are left with dozens of one off installations.  That is, every installation is a hand built package that is different than every other.  One cannot compare cost, output, reliability nor any other factors because they are all different.  The new guys comes along and wants instructions, instead they receive a thousand different ideas. They are confused, frustrated, and annoyed. They return to the Van’s catalog engine page and select the firewall forward package that is fully documented and proven. They write a check, turn a couple of bolts, and go flying.

Back to my comment about being successful.  To measure success, one must know the goal.  My goal was to fly inexpensively with as little financial investment as possible.  To me, this meant that I needed to buy an engine, convert it for aircraft use, and install it for little money.  After installed, it needed to be affordable to feed and maintain.  I flew two Subaru engines in my Quickie Q2. Neither of them cost much money (relative to other engines used in general aviation).  Both of them burnt a relatively small amount of fuel and were inexpensive to maintain.  Without getting into exact dollars, I judge the experience a success. Piles of information about these conversions is documented here.  I flew these engines something around six hundred hours (from memory, I’m not going to go dig out the information).  I spent VOLUMES of time converting and getting these engines to work.  I enjoyed this “building” time, for the most part – I’m not sure my family enjoyed it though. I’d ask but none of them are around any longer.

31 thoughts on “What happened to the Subaru Aircraft Engine?

  1. Chris Bonnerup

    Very good article Jon,
    I’m going to post a link on Rotary Wing forum for my ‘friends’ to mull – you probably know some people on that site.
    To me, the Soob conversion for aircraft embodies the true sense of the phrase ‘experimental aircraft’. I am building an autogyro and picked up a 2.2 with VERY low miles for a song (not my singing!). As of now I am enjoying the engineering and learning as I go, probably as much or perhaps more than flying. Having 10+ (expired)hours toward PP-FW, I stopped because it was boring me to tears.

    And if my ‘one-of’, home-built, self-engineered PSRU works well after 40 hours of testing, I’ll most certainly post info and a wealth of data on the web for all to criticize, bombast, ridicule, etc. etc. – but it will be my ‘experiment’.

    Thanks for the post.

    1. JD Post author

      That would be awesome Chris! Best of luck on your project and stay after it. Sometimes it may feel like you are taking more steps back than forward but you’ll get thru it and love the result – especially since it is of your own creation!

  2. Thomas Hankamp

    Jon, thanks for a great response,as I totally agree with everything you mentioned and that is why I will attempt to power my slow build rv4 with a direct drive recamed 2.5 ,otherwise as stock as possible.I am firmly convinced that people think they are smarter than the OEM people are wasting their time.I will use everything that my2.5 was designed for.I think most of us are il prepared to remove varioable valve timing at this time.
    Tom Hankamp

  3. Joe

    Jan Eggenfellner may have had a good idea but when he took money and failed to deliver props and hardware, he turned into a crook.
    He is now selling Honda packages, after having stole hundreds of thousands of dollars from his original customers. I purchased one of his conversions from two friends who he ripped off. I am returning it to use as a vehicle motor in a sand rail.
    Jan is lucky that someone hasn’t taken him out for what he did.
    My friends are out over $ 40,000.

  4. Ken Sorensen

    I enjoyed your article.My father and i have built a RV 9-A, and did not want a Lycoming engine. we wanted a affordable engine. And decided on a Subaru EJ 25. we kept it as original as possible but had to modify the oil pan and cooling system, fuel system. It was a challenge for us and at times frustrating trying to find help in our project. but now we have over 100 hours on it and have very much enjoyed the plane. the low fuel burn is great, and we can afford to fly. We may find additional bugs to work out but, that is why we built an experimental. To other builders we would like to say keep the faith and you will have success. If we could do it, you can!!!

  5. Marco Brando

    Hi, Mr. Finley.

    I like your site, very informative in every sense. I am a new pilot (only 100+ hours) and have good skills in mechanics and electronics. Like you, I chose EJ22 to make my homebuilt.
    One thing I noticed is, did you have to reprogram new codes into the ECU for fuel mixture at high altitudes ?

    Thanks a lot and keep up the good job. Apparently you are the one who will open the market after time-rating your machine for life cycle of all components !


    1. JD Post author

      Thanks Marco! I initially used the stock Subaru ECU. This worked but I was not happy with the inability to tune it. I then switched to the Real World Solutions EC2 controller which is programmable. I loved that unit and spent a lot of timing tuning it.


  6. John

    Your conclusion of “no market exists for Subaru” is wrong. The proper conclusion is the Subaru does not
    make a reliable, trustworthy, aircraft powerplant and has higher fuel consumption and failure rates
    than traditional aircraft engines. Ask anybody operating one how many engine-outs or failures they
    have had. How many overheats, how many gearbox changes. Experimentation is fine, but this engine
    option has progressed past investigation and experimentation, and has decidedly become a non-player
    if you want a safe, reliable and efficient airplane powerplant.

  7. ted kiebke

    i have a subaru engine that i want to use as a aircraft engine i am interested in going direct drive do you have any plans for sale that i can get

    thanks for any help


    1. JD Post author

      No, sorry. Don Parham used to have a book but I think it is long gone and certainly doesn’t apply to the newer, more complex engines (unless it has been updated). It really is a DIY project.

  8. Jarod Officer

    Very nice article, Jon. I’ve been following the Egg story for several years. It’s so unfortunate that Jan didn’t take a better approach to testing and supporting his product, much less delivering what was paid for. He seems to be a gifted engineer and attention to detail on his engines was pretty impressive. They sure LOOKED like beautifully-crafted engines. I’m curious what people think of the latest versions of his engine with the Gen 3 gearbox. Did he finally nail the design, albeit too late? In other words, is this an engine and PSRU you could buy, install, and fly behind without having to keep tweaking or otherwise re-engineering things? I’m curious, because I’ve seen brand new ones being sold cheaply. I’m assuming most of these sellers were nervous about either the reliability or the future lack of support or parts availability from Eggenfellner. I’ve noticed his old site it long gone. It’s just Viking engines now, with no mention of Subaru anymore. He truly ran away from it. Any opinions on buying a firewall-forward Gen 3 Eggenfellner engine package (for less than $10K)? By the way, it’s interesting to note the similarity with the Mazda rotary engine world. No firewall forward engine packages, and very few PSRU makers still active.

    1. JD Post author

      Thanks Jarod! Based only on the information that I heard from the owners of the later model Egg engines, I would stay away from them. These were the engines in which the internals were modified. I believe at least one of them failed due to the poorly made modifications to the variable valve timing system. The SDS EFI system that came on some of these engine is an excellent system. The problem is that it was never properly tuned (and that was Egg’s responsibility, not SDS’s). I’ve heard that the Gen 3 was an improvement but I think most everyone had quit flying them by that point so I suspect very little fleet time was ever put on them – meaning they are unproven, in my opinion. If you are a real experimenter, have an airframe that has superb engine out/off field capabilities, have another airplane to actually fly (if that is a goal), don’t mind tinkering for the next 5-6 years, and don’t mind throwing it all away in the end, the Egg engine might be an acceptable starting point. If it were me, I would stay away from them. (my apologies to the guys that are trying to unload these FWF packages)

  9. DM

    I bought an SLSA with the RAM 115A EFI Subaru in it two years ago and I am still not comfortable with a long cross country. Cooling issues and rough running while transitioning from dual to single fuel pump seem to be the biggest hurdles. I love the engine but will I ever get to stretch it wings? Any suggestions would be greatly appreciated.

  10. Peter Ming

    I’m flying a Kitfox with a Subaru Engine.The Engine has now about 850 hours on the Tach and I fly it over the Swiss Alps sience more then 15 Years.Until now,I didn’t have to many Problems with it.

  11. Keith Helwig

    …traditional general aviation motors are outdated garbage.

    Had a similar mindset prevailed in the automotive world, we’d all still be in Model T’s.

    “It was good enough for our grandfathers” is a terrible justification to still use these dinosaurs as aeromotive power. We tired of seeing the same outdated garbage from Cessna, Piper and Beech and set about building newer exciting designs….. where is the same spirit with respect to motors?

    Grumble all you wish about motors designed after 1930, but modern Subaru motors are quite amazing little things that are not only reliable, but economical as well.

    Too bad for the Luddites; but not everyone sees “not having to worry about carb ice” and “not having to fiddle with leaning” as “selling out”. Keep your antediluvian Lycomings and Continentals; if we wanted something that looks and sounds like the dog’s breakfast, we’ll get a Briggs & Stratton….

  12. Trevor Claughton

    I have an EA81 setup with a gearbox PSRU that works like a charm with some 125 hours on it. The EA81 has Subaru fuel injected heads and with the timing wheel on the pulley it also has the Subaru electronic ignition system. ECU is a Link Storm 4 made here in NZ and I have tuned it up using that setup, tuning is completely different from a car’s setup, it has a sensor that allows for altitude variations so no problems about mixture settings at altitude. Burn is at 13.5L/hr and the engine is great, starting first time and running smoothly with a 70″dia 3 bladed Bolly prop. Happy to fly over the mountains near my place up to 10,000 ft.

  13. matt

    Funny did a search of Subaru motors and airplanes after listening to a car talk episode where a guy asks that very question. nice to see a discussion about it. I think I would trust a Subaru 2.2 motor in the sky any day.I believe this may be the greatest motor ever made and am very interested in using it just for purposes on the ground. But myself always wanting to be a pilot maybe someday I will venture into the sky with one. Thank you for the article

  14. John Ragsdale

    Jan devoted 15 years of his life trying to adapt the Subaru to reliable aircraft use. Rather than
    question his motives or his ethics, let’s consider for a moment that the auto engine works
    best in the platform it was designed for, an AUTOMOBILE. The complexity of an auto engine
    is primarily to satisfy emission standards, and to take that complexity into the air represents
    an unacceptable risk. PSRU’s have always been troublesome, and are unnecessary if an aero
    engine is used.

    Yes, some ideas are not worth pursuing. I think Jan did his best, but in the end, discovered that
    he was facing insurmountable problems.

    1. JD Post author

      John – your comments sound good until one understands that Jan left many of his customers high and dry and IMMEDIATELY started a new company doing EXACTLY the same thing (converting auto engines for aircraft use) to a whole new set of customers.

  15. Trevor Claughton

    Couple of thoughts to the comments above.
    Firstly PSRUs have been used for years and like anything if done properly and maintained they work like a charm, witness the original Hipsano Suiza motors used in WW I in the SE 5a fighter et al, a solid V8 configuration that was later used cars. One of the all time favourites the Merlin, either RR or Packard, also had/has a gearbox PSRU up front and in modern day terms the Rotax engine does too.
    Secondly, with Subaru engines all you need to do is get rid of all of the smog control stuff and make sure that the clearances for the engine bearings are at their upper end so that you get lots of good cooling oil passing through them, just like VW used to do with their air cooled flat fours. Install a custom ECU that can control all of the ignition and injection and there it is. In my case the only thing that is Subaru EA81 is the block and heads, the rest is custom. Keep it simple.

  16. Hans Teijgeler

    Hi Jon,

    Long time no hear!

    I’ve experimented a LOT with my EJ-25 powered Jodel to the point where I now have a completely reliable, very powerful and very smooth engine package. I’ve got some 400 hours on it now and it has never missed a beat. Takeoff performance is out of this world (2500 fpm climb rate), with the engine sipping fuel at 5.5 gph in cruise. Maintenance is just changing oil every 50 hours. Cooling is spot on – I can idle the engine on the ground indefinitely, even on the hottest days, and then blast up to FL95 with the temp gauge never leaving the 185F mark.

    So indeed, like you said, it CAN be done. And I am very very happy with how the whole thing turned out. Like with you, it did add quite a number of hours to the project though… :-)

      1. JD Post author

        Hi Rob. I’m afraid you just missed it. I used to have all the details on finleyweb.net but I shut that site down a few weeks ago.

  17. Tim Bonner

    This has been a very interesting discussion. I am thinking about buying a Kitfox Vixen that has a new Subaru E81 fuel injected, turbo charged 130hp engine swinging a warp drive in flight prop. This was purchased from NSI. Is this a good setup. The engine was purchased a while ago and has only run for about .5 hrs. I am a little reluctant to purchase this plane with NSI not still in business. I read more bad than I do good about these Subaru conversions. Can anybody help me?


Leave a Reply

Your email address will not be published. Required fields are marked *