Just a couple thoughts on an auto engine. I researched that in detail because aircraft engines are flying antiques. Engine ignition technology from 1903. It really is hard to find a good engine. I would recommend that you follow tightly in someones footsteps that has a lot of hours on an auto engine if you are set on that direction. Ken Wardstroms Rover engine has been flying for about 10 years. There is Shillings Subaru in Alaska.
You can spend more trying to save money with an auto conversion. We have a friend with a Murphy rebel whose airplane has more hanger hours than apron hours. He bought a reputable redrive that gave out, bought a second, has been fighting cooling issues and rad configurations. Now he is putting the P51 style cooling shown in the March 2015 Kitplanes. He has spent money on a couple rad configurations, 2 redrives, headaches with cooling, custom engine mount and building a custom exhaust. At the end of it if he gets it flying this spring with the new cooling he is flying with his fingers crossed worrying about what bites next. He built that plane years ago and we have watched it spend more time in his shop that the air. He is technically smart but has been snake bitten taking this route. He will be the first to tell you that he would have save money buying & been happier buying a Lycoming 320 with a myriad of prop options.
The issue with auto engines is that eventually they pass into history meanwhile parts are still available for 50 year old Lycs and Conti's. Secondly most are geared 2:1 so that engine is turning 4400 RPM to cruise at 2200. So that engine will wear out 2x faster. Normally an engine with an overdrive transmission is running about 1800rpm and that is why a person can get years out of a car engine in a car. The one advantage is that liquid cooled engines consume less fuel than air cooled engines because of efficiencies of design, electronic ignition, fuel injection and ability to run leaner with less expensive fuel.
We bought an aircraft engine with 800 hours on it that came from a power upgrade. We bought a first run McCauley CS prop for 3500 and had it rebuilt for $2900 that needed basically nothing but a detailed inspect, labour and seals. Our engine is a Continental IO-360 that came with its challenges. We had the skills & support to be able to step off the path a little bit. If you go with the lycoming everything is available and there should be lots in S.America. There is so much support for Lycomings as you can get the mount from Bearhawk Aircraft, wide selection of props, electronic ignitions, Vetterman exhaust and the list is endless. If you can find a part time engine that is solid for $8500 & overhaul a prop or buy a rebuilt for $6500 that is a solid set up for $15000. You may even do better.
So again I recommend that you copy someone else's auto engine set up with a lot of successful hours because inventing your own set up could become a trail of tears. Here is a nice 6 cylinder auto conversion for the Supermarine Spitfire kits that is not a V8. It uses an Izuzu V6 which is pretty universal. It makes 250 hp without the weight of a Chev 350 engine. Lots of V6's are in the 250 - 300 hp range so should be able to stay away from a V8.
http://www.supermarineaircraft.com/options-v6-engine
If you are starting your build then build it with the 5 point engine mounts on the fuselage that you can mount anything to it. That will give you time to do your research and maybe find a good auto drive to copy or a good aircraft engine.
Check out props for engine auto conversions and what they require as well. May be limited choices there. I have read where a homebuilder can go through 2 or 3 props to find one that is successful. That is the headache our Murphy owner friend has with his Subaru. He has it pitched finer s that it can take off and if he coarses it out then he needs to long a run to get up to speed. We used a common engine and prop that are used for Cessnas of comparable size & commonly available. The blade lengths are adjustable, the CS prop has stops that are adjustable and a wide range of governors. Our set up was taken from an STC to up grade a Cessna to a Continental IO-360 that 172's use for floats.
All the best in you quest,
Glenn
BH727
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