You are right. The numbers are tiny. So the availability. What about the spare parts in such a scenario? The price also is not very attractive. And there is also another fact that might become an issue if not properly considered: the configuration of the engine. It needs a careful installation to keep similar the temperatures of the cilynders.It's been discussed many times in various threads. They are classic aero engines but support and availability have been spotty over the years. If they could get that part sorted and keep the price competitive I think they would be a lot more popular. See http://www.parmatechnik.cz/
I agree. A development using VW aircooled pistons/cylinders is very interesting. I've spent a very small amount of time on this but seemed to arrive at a minimum cylinder spacing of 112 mm. Most 4 cyl engines are closer than that but I did come across a couple of crankshafts: The Porsche 944 - 122mm and the Toyota 2/3RZ - 112mm.Personally, I would love to see someone do with the inline configuration what Verner has done with their 3VW and 5VW radials using VW pistons and cylinders. The inline is heavier than the equivalent flat or radial engine but it does make sense for getting the most speed out of a single-seater and just for a vintage look. Some of that weight can be saved because intake and exhaust can be more compact and you could even follow the example of the old Zündapp engines with the oil tank integral with the crankcase cover. Stock VW components and low RPM direct drive would only give you about 50-55 hp but it would still be good fun. A standardized intake, exhaust, and cooling arrangement including nose bowl, baffles, and outlet would make it easy to adapt to almost any design originally intended to use a VW. A Sonerai or a Taylor Monoplane with an inline would take on a whole different look and feel.
well...O-200, or any other 4 or 6 flat americain cylinder!What would you use for donor cylinders, pistons, and maybe heads for an air-cooled flathead engine? Off the top of my head, I can only think of Harley engines and I don't think those have been built since the 1970s.
To me, a key needed is a suitable donor crankshaft. Is a tough part to design/make otherwise. Needs an unusually large cylinder to cylinder distance to accommodate air cooled cylinder head fins. GM makes a 3.0 l marine 4 cyl. but I believe it was only 104mm spacing - seemed to close for the VW cylinders. O-200/O-300's heads would need even more space. Maybe the 122mm spacing of the Porches 3.0 4 cyl crank would be enough - not sure. I think I also same across an in-line, 4 cyl, air cooled gen-set diesel, which might be a potential source of donor parts - can't remember the make/model right now.3.3 l engines as four cylinder car engines are just out of good design. 2 to 2.2 l is about as big as they go. Some 2.5 with balance shafts. Car rpms just don’t make it work, to make that size four. Ferrari in the mid 50s made a racing four that big. If you can wrestle one of those away. Probably take a couple of million for just the engine if they would split it. Now that architecture or more easily copied the Alfa four could be turned into something. Wet sleeve block makes it easy to build a block. It’s just a box that holds a crank. Sleeves drop in. Nothing else but water pump and lower timing chain Head with cams is the top of the box. Find some forklift engine crank, expand the Alfa crank case design to the big crank. Rods, pistons and sleeves are relatively cheap to custom make. Leaves the head. Alfa head is pretty simple when it comes to heads. Off the shelf valves. Cams are easily custom cut. Add prop. If some guy in California can custom build a two cylinder and is from the pictures 10-15 engines on the way, just for the challenge, someone else could pop one of these out.