Greg writes:
<<<Thanks for your comprehensive input below.  You do bring up a couple of issues that we have only looked at in passing, and we will look into these issues further....>>>

When I evaluated the rotary for my IV-P my comparison categories were weight, power, reliability and cost. At an installed weight of 611 pounds (all accessories), 360 Hp (on the dyno),  a demonstrated 1,500+ TBO and a known cost the Lycoming was easy to evaluate. The rotary took an early lead due to its high power to weight ratio, low parts count, demonstrated high reliability (endurance racing) and relatively low cost OF THE CORE ENGINE. The fun started when you begin to add up all the support systems. The radiators (four of them, intercooler, coolant, oil and PSRU), pumps, tanks, filters, separators, coolant, plumbing and fittings, turbo machinery,  scavenging system not to mention the PSRU and the weight picture gets pretty bleak.  If you compare the firewall to prop weight of the two running engines you will likely find them to be quite comparable.

Since the rotary engine needs all of these supplemental systems to operate they must be added into the parts count and reliability columns. Each of these systems is critical to making power. One failure of a fitting, pump, drive, cap or coupling and the whole endeavor goes quiet.

One critical problem with the rotary is the accessory drive in that there really isn't one. The original  fan belt system is utterly inadequate for the additional power demands of the bigger water pump, scavenge pump, fuel pump and bigger alternator. One builder claimed he solved the problem by using electric fuel and scavenge pumps. When queried where the electricity came from he said proudly "The alternator!". Oops.  Serpentine ribbon belts are all the rage but they present a significant single point failure opportunity and FOD risk.

The rotary has the advantage in power IF you accept that the rotary will live for very long at 150 Hp per rotor.  Ask your engine guys how much power you can get for 1,000 or even 500 hours of continuos output. Remember that even a race engine is not 100% duty cycle. Even the left turn only crowd lifts for the turns. Derate the engine to a more realistic 80 to 100 Hp per rotor and the advantage evaporates. I fly my Lycoming at 75% power (270Hp) all the time with the exception of the climb (90%), the approach (45%) and racing (100%).

Then there is the question of drag. Consider this, as my friend and fellow engineer Fred Moreno once observed, thermal transfer rate is proportional the the temperature differential of the two materials. In an air cooled engine the cylinder heads run about 400 F and the air is around 0 F giving a 400 degree F delta. In a liquid cooled engine the radiator is running about 200 F so for the same ambient the delta is 200 F or half of what it is in the air cooled engine. You therefore need TWICE the air mass flow to remove the same number of BTUs. Radiators are so much bigger than cooling fins because they need to be. Cooling drag is a large percentage of the overall drag of our slippery Lancers so doubling that drag is bad news in anyone's book. You have the double whammy of cowling drag to cool the intercooler and turbo plus the belly scoop. One IV I know of that added a belly scoop for an air conditioner condenser lost better that 10 Kts. That whole "P-51 scope added thrust" story is a myth, IMHO.

You also mentioned a fixed pitch prop. I assume you are using this because you don't (can't?) have a propeller governor. How much performance will that cost you? (rhetorical question).

There is the matter of being able to use a lower grade of fuel (auto gas)  but  how many airports have auto gas handy. Notwithstanding my post on auto gas, it presents a logistical problem that makes up for its cost.

After adding it all up the rotary and Lycoming come in about even. You can argue the minutia, which engineers and builders love to do, but there is no elephant in the room that makes the case a slam dunk.  What it came down to for me was the simple question of whether I wanted to design and build and engine installation or build an airplane and go fly. Having already done the engine thing I decided to adapt the Lycoming. This only added about 700 hours to the build time. In the years since I have revisited that decision many times and have yet to regret it.

I am NOT saying that you are doing the wrong thing. If people built airplanes only to fly then they would buy rather than build. Builders build for the joy of creation. If building a new engine installation  is what you want then go for it. I wish you all the best and hope you have realistic expectations. If you are typical, when you are done the result will both please and disappoint. The empirical evidence is clear. Hangers across the globe are replete with failed and abandoned projects where hope and enthusiasm tipped the scale until that buzz kill reality stepped in and spoiled the party. This does not mean you shouldn't try. Every great new accomplishment  is built on a foundation of can't. Perhaps you are the one. Good luck.

Regards
Brent Regan