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Thread: Question: Auto engine conversion

  1. #1
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    Question Question: Auto engine conversion

    Hello, I just joined the site and am loving it so far. I am nearly ready to begin my first project and I have a couple questions about the use of an auto engine conversion if anyone can help. I know they are used some but not often what are the big drawbacks people find when trying to use a modern auto engine in an airplane? It seems to me parts would be much cheaper and more available but I don't understand why they aren't used more. Also, wouldn't the O2 sensor on an auto engine be able to control the mixure automatically? The onboard computer in a car uses this sensor to set the mixture more lean or rich for the most economical setting, shouldn't it work just as well in an aircraft? I am interested in learning as much as I can about this aspect of powering a homebuilt, thanks for the help.

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    You should get a number of great replys.

    Seems to me that the weight issue would be a fairly large concern...

  3. #3
    Registered User StRaNgEdAyS's Avatar
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    The use of the O2 sensor is only viable if you will be running unleaded, Aviation gasolene contains lead, which interferes with thier operation.
    Life is short,
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  4. #4
    Super Moderator Midniteoyl's Avatar
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    Well now... This is a topic that will take a great many posts to properly reply to..


    First off, Auto Conversions are used more than you prolly think, and a majority have had good success.

    Weight is not really an issue, since the all-aluminum engines used today are light, and the radiators used in aircraft applications are much, much smaller - usually holding only a gallon of water.

    The O2 sensor does indeed work to control the mixture, through the ECM, but as stated earlier, 100LL can clog it - but the jury is still out on how long that takes. Some have flow for a few hundred hours with no apparent ill effects so far.

    Positives in using an AutoConversion include - Stable temps, no 'shock cooling', cheaper to buy (usually) and maintain, usually higher torque at the prop compared to same HP lycosuarus, no mixture adjustments, variable timing so can lean more aggressively, easier to turbo, bragging rights, and more..

    Negatives include - Needing a PSRU (Propeller Speed Reduction Unit) to slow the typically higher RPMs of a auto engine down to exceptable propeller speeds (basically a one speed trans), needing to make or find a different engine mount, and maybe modifications to your cowl, among some others....

    There are websites of people who have done it themselves, plus 3 major players in the Subaru engine conversion field, 3-4 in the VW field, with 1 or 2 doing well on the V-6/8 side. Plus a Suzuki place here or there.

    What you'll need and want will be determined by what you're building and goals... What are planning on, and what engine where you thinking about?


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    Don't forget the Wanklers! By that I mean Mazda rotaries. Do a Google on aircraft (or airplane if you must) conversions [insert fav brand name here] and see what comes up.

    Another approach by www.jabiruengines.com.au is using auto parts in an all new certified engine. Buy your sparkplugs from Autobarn.

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    The biggest issue by far is the conservitive nature of aviation.
    The majority of aviation will not support new and untested ideas untill they are proven, which leads to the catch 22. How do they get proven if they are not tested and tried?

    Automotive conversions have a long history of failure and disaster. Untill recently auto engines sucked fuel and were heavy. One positive effect of CAFE standards is it has driven the technology of autos to build very reliable and efficient light weight machines.

    In order to compete auto engines have to offer a very significant advantage over traditional proven soluitions. It is only recently that auto engines have been able to offer similar weight, a significant savings, as good or better reliability, less operating cost, and simular and less inital cost.
    Critical components that have completed the package are now avialable off the shelf, with a proven history. For example PSRU's are now being manufactured by a few people and the ECU's are off the shelf components using the latest automotive sensors.

  7. #7
    Super Moderator orion's Avatar
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    As with any aspect of homebuilding, the choices you make regarding you powerplant will depend on many factors and as such, it will be important to do your homework before jumping in.

    Automotive based powerplants are certainly an option and despite many roumors and bad press, the ones in service today have had a very successful and safe history. In doing this type of installtion though, it is important to keep in mind that the environment that the auto engine sees in a car is substantially different than the one it sees under a tight airplane cowl. I've seen several installations where the owners had to do quite a bit of tweaking before they got all the sensor to work right once the cowl was on. (My reccomendation is actually to build up an engine from scratch and try to eliminate the black boxes - but that's just a personal choice.)

    The auto-based aircraft engines do tend to be a bit heavier than the standard aircraft engine but the difference is not all that significant, especially if you use many of the currently available aluminum or magnesium components.

    The auto engines have a substantially lower specific fuel consumption (fuel burn per hour per horsepower), with the exception with the rotarys, which tend to be in the same ballpark as the standard airplane air-cooled engine.

    The only significant drawback is the reduction drive. Quite a number of the reduction drives out there have surprisingly little engineering behind them and very few companies seem to be willing to develop a complete and tested installation package. Some do engines, others do some form of redrive, but rarely do you see one company doing both - and that I think is the major problem the auto engines have in breaking into the market in any significant numbers.

    The bottom line is that the auto engines are a viable and potentially beneficial option to power your airplane. You just need to do quite a bit of homework, especially on the technical end, before selecting the right one that will meet your needs.

    You can also do one yourself but here the drawback is that if you are not intimately familiar with engines and aircraft applications, you could get into trouble. Doing one from scratch may also sound cheaper but many have found the hard way that they will often spend much more than if they went out and bought a Lycoming.

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    Registered User wally's Avatar
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    Direct Drive Chevy V8

    I don't have much info on it yet but our EAA chapter 182 pres. now has his own design flying. He is using a direct drive LT1 Chevy V8. I have seen the plane up close but not seen it in the air yet.

    The cowling looks a little strange, well the whole plane does for that matter but IT FLYS.

    A PSRU gives you more HP to work with tho.

    I have another friend who flew a Rans S-7 for several years with the Stratus Subaru engine and belt drive. He loved it. He switched to the HKS air cooled twin to save a little weight and just to be doing something else.

    Wally
    Last edited by wally; May 3rd, 2004 at 01:57 PM.

  9. #9
    Super Moderator orion's Avatar
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    The direct drive configuration is certainly a viable option. It requires a somewhat different approach though. Basically, horsepower is a function of torque and rpm however, airplane engines really need torque to deliver optimal performance. This is why redrives are commonly used on auto engines since the basic engine, being generally smaller in displacement on a horsepower level than the conventional aircraft engine, needs the rpms to deliver the necessary power in order to have nearly the power density equivalent to an airplane engine.

    If you direct drive the engine, you must approach the engine design as you would for a truck engine - in other words don't go the horsepower-rpm route, concetrate more on the torque. In this way you can achieve nearly the same power to displacement to rpm ratio that an aircraft engine can (if you boost you can actually do much better), all with direct drive. In order to do this, you will need a somewhat longer stroke on your crank, as well as a cam profile and ignition system that is optimized for this type of operation.

    The ideal configuration would be to have an inverted engine installation, so it could fit within a realtively standard cowl. This requires dry sumping but this is not all that difficult to do - all you need is to reroute some of the pickup and sump lines, as well a do a bit of modification on the engines internal oil baffles (in order to prevent piston hydraulic lock).

    Since an auto engine crank is not designed to take the prop loads, you will also need a seperate output shaft, which is supported in its own housing. This will need a coupling between the crank and the output shaft that is designed to dampen any torsional feedback into the system, something that the auto engine crank isn't designed to handle. I know several folks have connected the output shaft directly to the flywheel but this is something I personally would not recommend.

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    Auto engines

    Auto engines have a very long history in homebuilding, with the Ford Model A and T supplying power to many of the inter-war year designs.
    Probaly the most popular auto conversion engine is the VW. THere are several suppliers and you can get a good proven engine of between 60 and 135 HP for between $4k-8K. The most popular ones are the Revmanster, Great Plains, and the AeroVee. Valley Engineering makes a great belted redrive. THere s also an outfit in Austrailia I think that makes PRSUs for the VW. Texas something.
    Ask Johnny Luv's Biplanes about the Corvair conversion.
    Raven Redrives has a whole series of engines based on the GEO/Suzuki line of engines.
    There is a company currently marketing BMW motorcycle engine conversions too.
    On the lighter side there are the 1/2 VW conversions, and one built from a Citroen.
    Most of these are smaller engines for light planes.
    Geshwinder (or something like that anyway) has redrives for Ford and Chevy V6 and V8 engines. They advertise in the Sport Avaiation and Kitplanes classifieds. There is another company that does these bif beasts as well, but I can't think of the name.
    There are at least 2 companies doing Subaru conversions - eggenfeller is one - one outfit has firefall forward solutions for thGlastars and RVs.
    Then as someone else mentioned, there is Terry Crook and his gang working on using the Mazda Rotary engines. Terry flew over our campsite at Sun n Fun at the start of the race - weird sounding plane.

    I'm building a Great Plains 1915 VW with a Valley Engineering re-drive for my Acrolite project.
    We can do it!

  11. #11
    Registered User pylon500's Avatar
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    Ford Model A and T, VW, Corvair, GEO/Suzuki, BMW motorcycle engine Citroen, Geshwinder, Chevy V6 and V8 engines, Subaru and Mazda Rotary.
    But if you want to have a look at something unexpected, have a look at this site;
    http://aek4470.finalnet.cz/html/muzeum.htm
    As a site, it's seriously buggy, and I can't get the thumbnails to load, but what you can see of the engines is mindblowing.
    A quick rundown; these engines are from the Czheckslovakian auto company TATRA who are probably better known for trucks, but also build (and have since the early 20's!) limousine class cars.
    After starting with small air-cooled flat twins, they moved onto flat fours and then stepped over to V-8's!
    Their latest engine is around 3.5 litre, quad cammed and turbocharged to around 250 horse power and AIR-COOLED!
    There's some shots here of one in bits (also a bit buggy);
    http://aek4470.finalnet.cz/html/go.htm
    Only a two valve head, but a second plug looks pretty easy to do.
    And I'm fairly sure it's all aluminium.
    Some other shots from the first link show some of the truck engines;
    5.25 litre, air-cooled, torbo-charged V-12's!!!
    Thinks,Leave the fan on and put it into a 5/8th scale Aircobra!
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  12. #12
    Super Moderator orion's Avatar
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    About four years ago or so I traveled to Prague and to the Eastern part of the Czech republic to meet with Tatra in order to secure the rignts to import a small aviation engine they were at the time developing. After getting a tour of the factory, the engine that I actually wanted to import is the V-8, and a smaller V-6 based on the same block.

    Yes, it's all aluminum, solid state ignition, as well as a new Bosch injection system. A beautiful engine - but with a relatively less than beautiful price tag. Due to the competitive international market place, the Tatra cars, which are somewhat dated in several aspects, do not tend to sell all that much and as such, the production line is virtually at a standstill.

    You would think that they would be interested in new markets. Well, in short, they are however, due to the low volume of production my cost of the engines was to be in the neighborhood of $12,000 each. That was for a ready to run engine but still without reduction drive nor accessories.

    They did offer to add a reduction drive and keep the price relatively unchanged but by the time I added in the development cost of working it into a firewall forward package, the issues of shipping and importing them here, overhead, insurance, as well as any thought of some level of profit, I would have had to sell them for something in the mid to upper $20s. Then there were uncertainties about parts, factory support, warranties, etc.

    The baseline V-8 in this application would have produced anywhere from 160 hp to just over 200 hp (max. continuous), depending on a few internal details. The installationn weight was just about equivalent to a Lycoming (OK a few pounds more, but not much) and the specific fuel consumption was in the neighborhood of about .45.

    In short, it is a beautiful engine but the logistics were far from ideal.

    Since then the company has changed CEOs as well as a number of other top people so the aviation interest disappeared.

    The small engine they were producing (flat four with about 90 hp) was purchased by a small group of investors, two of whom were the developing engineers. I followed their progress for a while - they did get the engine completed and did get the JAR airworthines ceertification. Since then though, the project seems to have faded away and I haven't heard anything from them in about two years. Too bad - it was a much nicer engine than the Rotax 912.

  13. #13
    Super Moderator orion's Avatar
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    Here's one of the pictures of the Tatra V-8 bare-bone engines before all the accessories are added. Would make a perfect airplane engine, especially since you'd get the smoothness of the V-8 but without the added systems of the water cooling.

    The item in the middle between the cylinders is the oil cooler.
    Attached Images Attached Images  

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    3800 series

    I plan on using GM's 3800 series V-6 mostly because I already have an available engine that can be rebuilt with all the eletronics already attached. I want to continue to use unleaded gasoline for cost reasons mostly but encorprating the O2 sensor sounds like a nice idea for the mixture control. It's good to know people have been successful with that so far. I am still undecided about a PRSU but would like to use a sort of belt drive, however, I am not sure if any available are big enough for 200+ hp engine.

  15. #15
    Super Moderator orion's Avatar
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    Personally, I am not a fan of belt drives just because in virtually all the designs I've seen, the drive is pretty much open to the breeze and any possible contaminants that might be coming in the cowl, or that are being circulated within the cowl, have a direct access to the belt and cogs.

    However, out of the several belt systems available, the company Northwest Aero Products seems to have a good configuration that quite a number of people have had good experience with. It's at leaast one option to look at.

    Personally I like the silent chain configurations, even though you do end up with a bit more weight on your nose. Probably the best designed/engineered one is the unit developed originally by Fred Geschwender. The redrive is now being produced by Aleternate Air Power (at http://www.alternate-airpower.com/). It's a bit more expensive but my belief here is that this is one area not to skimp on and in general, during that past several years, it does seem that you really do get what you pay for when it comes to reliable redrives.

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