I intend to build small aircraft as I explained here. But I am quite confuse to chose the BEST engine to be used. My requirement is range from 60HP to 100HP. BEST in here is considering the price, the weight/hp, the easy maintenance, and everything. By comparing all, we will get what is the best one to be used.
Main issues with auto conversions:
They are run very hard compared to aircraft engines. The same engine in the car runs at 20% power cruising on the highway. This application is equivalent to pulling a trailer in a car that loads the engine to 75% rated power at its torque peak all the time. However, that doesn't disqualify it if it has a track record. Subarus are particularly robust in this regard.
Reduction drive torsional resonance. It's been the bane of auto conversions for many decades and most of the solutions are only partial ones. The engine has to demonstrate no torsional vibration modes and that the drive system is robust enough to trust with your life. It's a major point-of-failure that you avoid with direct drive.
Fuel system. I would prefer a regular carb myself. If FI, it MUST have a fully redundant electronics package, with no single points of failure, because with solid state electronics they are either working or not and there is no degradation to warn of potential failure.
Same with ignition. I can live with single plugs, but the electronics must be fully redundant with no electronic single points of failure.
There are a lot of other details, like the crank. Is it a forged crank with properly radiused journals for stress crack resistance?
The great thing about "old fashioned" aircraft engines is that they are very "undertuned" and understressed, and will still make power with shocking amounts of internal degradation and damage.
I would think of that engine as being equivalent to an O-200 (in spite of the claim of 117 hp) which is about 18 pounds lighter, with dual redundant ignition and a simple reliable, carburator, no reduction drive failure mode, no cooling system failure mode, etc. etc.
If it was me, for that kind of money I'd hunt for a good mid time O-200. At any rate I would want to see a lot of hours accumulated on the auto based engine to provide some kind of probability comfort zone.
Another really good alternative engine option is a Corvair. Flat 6, air cooled, carburetor, semi-dual ignition and can be modified to dual plugs, silky smooth with that awesome flat 6 sound. They are very robust and do not run at stress levels much more than the original car application.
If it was my project I'd be going with either a used O-200 or a Corvair.