As I understand, the reason a typical car engine can’t sit at 100% duty cycle isn’t the engine itself, but usually the cooling and oiling configuration.
Examples:
Looking over the Viking engines, I don't think it's fair to call those "automotive engines," because my read of the description of what they do means they're pulling it apart and replacing an awful lot of pieces. They claim they're "based on" the latest Honda engines, and once you're starting to change the cylinder bore offset, custom hone the cylinders, replace your pistons and conrods, etc, it's no longer a car engine.
On their About page, they themselves say:
> Companies like Honda and Mitsubishi have spent millions of dollars refining and testing. We don’t claim that we can outsmart either company when it comes to the design of any internal running component of these engines. We don't change vital engine parameters around and claim we have different models. The compression, etc. is all stock. Every part is OEM Honda / Mitsubishi, nothing is new aftermarket from unknown origins.
> We start with the most up to date year engines with super low mileage, derived from fender benders across the US. When customers want the information about where there engine core came from and how many miles it had - we have all that documentation readily available to show.
Literally, every one of these engines came out of a car. I think that plainly qualifies it as a car engine.
Marine applications generally means salt water, so they will run at higher power is the salt is what gets the engine eventually not the stress of high power output. Airplane engines are expected to be reliable and so they run at relatively lower power output. There are many small niches in between that have their own idea of what 100% duty cycle is.
This exceeds most definitions of "100% duty cycle".
The XTS-210 can do that?
Our flying club engines in the 172s typically make at least 3000, if not 3500 hours, and I think some of the overhauls at that point have been a "Well... it's still perfectly fine... but..." thing where the board was just starting to get uncomfortable with the hours on it.
And, yes, they spend a lot of time making less than rated power, because of density altitude, but they're still rated for full power operation, and since there's basically no wear going on with an engine in operation (almost all the wear is during starting), there's no real difference there.
It's not until you get into the really large engines where "maximum continuous" is a different thing from "takeoff power." The turbocharged 500s are about the smallest I know of with that sort of rating, and even then I don't think it's all of them. Most of the big radials have that limit, though. If you find a smaller plane with that sort of limit, it's either a possible resonance issue between the engine and prop, or a noise regulation for certification.
Go ask your Camry engine to make 100% rated power indefinitely, and see how long it holds up. That's the difference.
A typical car engine is designed to make 30-50hp sustained, and occasionally generate more power for reasonably short periods of time.
An aviation engine, generator engine, or any sort of "industrial" engine is going to be able to sit there, making full rated horsepower, for thousands of hours without any trouble at all.