Should you use a standard aviation airplane engine?  Or should you convert an automobile engine?  There is a lot of discussion on this topic all over the net, at EAA meetings, and at fly-ins across the country.  Here are some of the main topics I’ve heard, and my views on them:

Myth: Aircraft Engines are easier to install.

There are a couple of firewall forward kits that make it just as easy to install an auto-conversion as it is to install a standard airplane engine.  Eggenfellner, Vesta and Powersport offer everything from small, turbo charged engines to LS1 Corvette engines to Mazda Rotaries.  These are just a few of the companies that have engine kits in the 200HP range for an RV-8.  So it shouldn’t be any harder or take any longer to install than if you bought a Lycoming engine and Van’s firewall forward kit.

Myth: Aircraft engines are safer.

True, the standard airplane engines have a lot more hours flying than auto conversions.  That fact doesn’t make them safer.  If we followed the logic a step further, we would have to buy a factory built airplane instead of building our own.  No thank you.  Lycoming and Continental failures happen all the time.  Planes land with one jug fouled, on one mag, or after throwing a rod.  But nobody makes a big deal of it, it is the way these engines are.  But when one auto-conversion lands with a problem, there is a lot of press and commotion.  I believe this is the manufacturers and distributors of the standard engines working their public relations and marketing, not necessarily the truth.  The newer auto engines have been factory tested and are safe.  Yes, now and then they fail, but no more often than the standard airplane engines.  I don’t know of anyone who has done the study and run the numbers to compare failures per flying hour.  So until then, all we have is opinions. 

What about price and parts availability?

Initial Cost.  Most auto conversion kits cost around $30,000 by the time you have everything installed, including mount, cowl, and prop.  Some are cheaper, some more expensive.  A new Superior XP-360 engine costs $20,000 just for the engine.  By the time you add accessories, mount, cowl and prop, it will cost about the same as most auto conversions.  You can lower your firewall forward cost by putting together your own engine package, it will just take more time and effort.  "But wait" you say, "Vans includes the mount and cowl in the price of the plane."  True, but if you are installing a different engine, you can get the Finishing Kit price reduced by not ordering the mount and cowl. 

Lifetime Cost.

The real savings come during the useful life of the engine.  Parts for airplane engines are almost 10 times more expensive than those for auto engines.  You’ll pay about $500 for a new aviation alternator and at least $250 for a rebuilt one, while an auto alternator will run you about $50.  An aviation fuel pump will run about $200 while an auto one is just $30. 

When you reach TBO you will really see the difference.  The average airplane engine overhaul runs around $20,000.  The average auto engine overhaul runs around $2000.  In fact, you can buy a brand new auto engine and throw your old one away.  Now you have a zero time engine and over $15000 savings.

Parts.

Parts availability is almost always better for the auto conversion.   Let's say one Saturday you are flying behind a Lycoming and stop in for that $60 hamburger at your favorite small airport when the voltage regulator stops regulating. You have a couple of choices.  You can charge the battery while you eat, then get home on minimum electrics and repair it at home (I don’t ever recommend doing this), or you can ground the plane while you wait for Monday when the part can be sent from a warehouse.  If the same thing happens with an auto conversion, you get a ride into town, stop at the local AutoZone, and you can be home before the day is through.

Bottom Line:

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