Indeed scr4, you hit the nail on the head there.
All things being equal, a 300hp engine which is 7 litres in capacity and works extremely free of stress will always, without fail, outlive and out “maintain” a highly stressed 2 litre turbo engine say, which delivers the same horsepower.
Oddly enough however, within reason both of those engines will deliver similar fuel consumption figures - and the reason for that is as follows…
Regardless of engine design, or engine breathing method, or valve actuation, or cam shaft placement - all things being equal - horsepower costs fuel. Every internal combustion engine requires a coolant system of some sort to prevent the engine block from melting. Accordingly, even in the most esoteric Formula One engine, still to this day after 100 years of development, over 60% of the potential energy in a given amount of fuel is lost to the coolant system. When you throw in mechanical friction as well, due to such factors as your gearbox and your drive train - a modern F1 engine delivers 38% fuel liberation to the back wheels. In most road going engines, that figure drops to somewhere between 32 and 36%.
Hence, the issue is not so much what engine configuration works best, but rather, how much horsepower do you truly require in your daily life? Sure, some folks like to have 500hp in an AC Cobra replica, but that 500hp still burns the same proportionate amount of fuel if you see what I’m getting at.
So, once you’ve got an idea of your horsepower and torque requirements, then in theory, an engine which delivers those requirements in a lazy non-stressed manner will ALWAYS outlive another engine which delivers the same performance, but does so in a highly stressed manner.
Obviously, a heavier vehicle will influence fuel consumption per distance travelled compared to a lighter vehicle too.
So, in short, after all these years, the consensus is this - a well tuned push rod 2 or 4 valve per cylinder engine with a modern electronic fuel injection and engine management system is going to be the winner - at least in terms of longevity. They have fewr things in them which can break - which in turn means that they have fewer “weak links”. And THAT is what we perceive as being a “bullet proof engine”.
Down here in Australia - in the late 60’s, GM, Ford, And Chrysler all invested heavily in local car manufacturing facilities. As you know, Australia’s a pretty hot and rugged place - so our locally designed engines were modelled on the American formula - as averse to the European or Japanese formula. It’s still very common to see 30+ year old Aussie made cars with “American style” engine designs working like old workhorses.
Indeed, more than a few Aussie tweaks and refinements ended up in their parent companys back in Detroit as a result.