I would guess that whatever makes it cost so much would equally apply to this solution once it is certified and not experimental. The gas V8 will be much less fuel efficient than a small turbo diesel, especially at altitude where the turbo offers huge advantages.

Those Mercedes engines are found in small cars and delivery vans around the world, and are widely available and pretty cheap. For example, the Centurion 3.0 uses a Mercedes-Benz OM642 which is found in Freightliner/Sprinter vans, Jeeps, and tons of other very common cars. You can buy these engines straight from Mercedes for like $8k.

In this case, the author mentions using an aluminum marine GMC V8, but not which one exactly. This is most likely based on the LS V8s, which are fairly expensive motors, and a pretty ancient design (e.g. pushrods).

> I would guess that whatever makes it cost so much would equally apply to this solution once it is certified and not experimental.

Bingo! Yeah, I was wondering the same while reading the article.

> a pretty ancient design (e.g. pushrods)

Does it matter? The engine is significantly derated vs. the original car engine, so max rpm is going to be much lower, thus no problem with valve float.

Modern direct injection diesels still use OHC, even though they run at really low RPM, so valve float can't be the only reason virtually all modern engines use it. I think this is because it allows for larger and better positioned valves, or even more valves (e.g. DOHC/4 valves per cylinder), making the engine breath better. I imagine the advantages of that would be even greater at altitude.

I'm not saying OHC aren't better, they certainly are (in most respects). Just saying that I wouldn't consider pushrods a showstopper either.

(As an aside, when aviation engines started going with 4V designs in the 30'ies, it wasn't only about breathing, but better cooling of the valves was an equally big motivation.)