At one time, the Egg installations were using what looked like either GM or Ford air conditioner evaporator cores. Fairly common for a while in rotary engine installations in RV-x's. But the 'box' for an inlet is just astounding. It's amazing that they didn't all melt something before getting to pattern altitude.
Charlie
The idea of the box was to catch as much air as possible coming in the oval RV inlet. The entire system was initially set up for RV's using the cowl as is. Jan achieved some success with the arrangement in the blue RV-6A at the time however the airplane was tweaked by an expert tweakier. He had no cooling problems with it. The box front was closed except where air entered through the oval inlets.
I flew with Jan one calm morning at OSH and it did better than the 185 he advertised with oil and coolant temps very normal. But it was a finely tuned super charged H4 running about as smooth as wrist watch. He demoed that airplane a lot and it sold engines, more than he could deliver for a few years.
I had a major overheat on the first flight with the H4, never left the traffic pattern. Sitting in front of the hangar running the engine, I discovered if the cabin heater valve was opened, the engine cooled instantly. The problem was the thermostat. Subaru has it at the coolant intake to the engine not at the exit. It was not opening because a small amount of heated by-pass fluid was not getting to it. The heater fluid was and it opened it. Subaru engines are like that, they need heated by-pass fluid to open the thermostat. From then on it was recommended the the heater core valve be open or removed.
Actually, I was getting along quite well with the H4 after that although clearly it was not making 0320 HP. Cooling was an issue but manageable and it was a fun airplane to fly with the Quinti prop system. What did it for me with the H4 was an off field landing after a timing belt failure. I was so satisfied to that point I decided to do it again with the H6 (and its internal timing chain rather that the belted H4) thinking it would certainly duplicate the 0360 in performance. It did not. RV-7A performance was off by at least 15 knots.
The engine also had major cooling problems with the same H4 radiators. I flew it all year 'round for 5 years but never without some special procedure to keep the coolant temp below 230. Once up to 8 or 10 thousand feet it was OK but it took a while to get there. Jan offered to sell a couple of the larger rads that came out later but I was not in a good mood to part with another $900. He made money on the H4 and H6 with me and I was beginning to wonder when it would end.
One day when it was in the 90's the MT electric brush blocks dropped off the rail right after take off, the prop was stuck in fine pitch. One method of getting adequate air through the rads was to set 1700 rpm at WOT. It always caused a drop in coolant temp but that day the prop was churning at 2600-2700 pushing no air at all across the rads. The coolant temp was over 250 by the time I got on the ground. I believe the recommended Subby coolant temp is about 185 - I figured the engine was toast. Actually, it wasn't. I gave the engine to a guy in Atlanta who tore it down and measured everything, it was like new according to him. So go figure....maybe the H6 is tough as a Lycoming. It sure did well at take off power and 2600 with the MT prop but lost some of that guts in cruise.
However that event torqued it for me with Subaru and I don't look back for a minute, I'm glad to be out of it. I had to quit flying or change to Lycoming as this was no fun at all anymore, the problems were not going away.
So, Lycoming it is for me - for as long as I can push the throttle up and not bend metal.