Engines
Like a hunter, I studied my prey carefully.  White, grazing at various airports around the country, the graceful form of the Long-EZ/Cozy aircraft have a lot of differences.  There are many flying with Lycoming engines.  These are the officially recommended engine for the aircraft.  They are also a very old design with known flaws and tendencies that have many.  There are Franklin, Jabiru, Rotax, all sorts of certified engines flying in these experimental aircraft.  But then, there are also the non-standard propulsion options.  Subaru and Mazda are the immediate winners of this popularity contest.  The solid Subaru engine, the 3-moving-parts-high-power Mazda 13B, these guys seem to lead the pack and have active builders fabricating and flying them every day.  There are others, including Ford V6s, jet engines, and even rockets!

Mazda 13B Rotary
I expect to learn more over the course of my build, but right now, my gut feeling is that I'll be learning more about rotary engines in my future.  Specifically, the Mazda 13B (of the RX-7) mentioned above appeals to the engineer in me.  Three moving parts instead of something like 26 in a reciprocating piston engine.  Great power to weight ratio, and perhaps most importantly, there are real engine heads out there who have done a lot of the trailblazing for me that I'll be able to take advantage of.  Every piece of experimental data collected and acted on from other people reduces my costs, increases my success probability, and improves safety.  The cost....  is not a small factor either.  I could spend $30k+ for a certified Lycosaurus, the $14k+ to-rebuild-after-2000-hours setup that mechanics love, or I could spend under $10,000 to buy a low-mid mile rotary, have it professionally rebuilt and modified and have an engine mount fabricated, a tested PSRU (propeller speed reduction unit, more later) and a also get a big community of builders to draw on.  I suspect I could do a lot better than $10,000 if I pay close enough attention to other rotary flyers during the years it takes me to build my plane.

What about the Renesis?
Another rotary engine of note is the new Renesis that powers the RX-8.  It's supposed to have better apex seals, better port positioning, and offer more power in a lighter package.  It's also quite a bit more expensive as there's a smaller stock to choose from.  At this moment, the 13B is still my preference.  Part of this is the cost concerns, of course, but even more importantly, it's unproven in aircraft.  There's a lot more experimental data to pull from the pool of 13B flyers, and the limited Renesis data I've seen so far doesn't fall over itself talking about how incredible it is compared to the older gear.  Specifically, I've been reading Rotary Aviation's testing, and it's been a bit lackluster sounding so far.  I'm sure things will change, but it's still up in the air.

I'm sure this decision will develop and may even change as time passes, but for now...  I hear the word 'wankel' and don't chuckle because it sounds funny.