The engine comes from an unbuilt British sports coupe.
The Mazda MX-5 Miata continues to be a popular choice on the used market for folks looking for a classic two-seat, rear-drive sports car that's also fairly affordable. In stock form, the Miata is not especially powerful, though, but these guys are fixing that by cramming a V10 engine under the hood.
This is a very rare V10, too. It displaces just 2.0-liters and is for the unproduced Connaught Type D Syracuse GT. The engine makes around 200 horsepower (149 kilowatts) and over 230 hp (172 kW) in supercharged form, which this one might be when the project is done. Similar to the Volkswagen VR6 engine, this one has a narrow enough angle between the cylinders that there's only one head, rather than two on most other V-configuration powerplants.
The video largely focuses on tearing down a second-gen Miata to remove the powertrain, so that the V10 can go in its place. Before installing the new powerplant, the body and remaining mechanical components will get a full restoration. Then, the owner will ship the car for the new powertrain installation.
It will be an interesting story to follow. This will possibly be the only V10 Miata in the world and will certainly be the only one with a Connaught engine.
If you're curious to learn more, check out the video above that has an interview with Tim Bishop, the creator of the Type D and its V10 engine. He's to the point by saying that running out of money is the reason for the car never coming to fruition. The original plan was for this powerplant to have hybrid assistance, which was innovative by the standards of the early 2000s.
The clip also shows the engine running. In the more recent video, you really only get to see the engine block. On the stand, the head is in place so you can see the complex exhaust and intake arrangement.