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It depends on a lot of things, but I think it's only meaningful if you're comparing similar engines.

I believe it's pretty well agreed that if you take two identical engines, and increase the displacement of one, the bigger displacement engine will make more power. So, if you want an engine with smaller displacement to make the same power, you have to resort to other methods, like raising the compression or forced induction, which put added stress on the engine. Think about it - the power of an engine comes from the force of the fuel exploding in the cylinders. The more powerful your explosions, the more powerful your engine, but more powerful explosions mean more stress on the components. The more power you want to get out of an engine, the more stress you put on it. Now, a good engineer will correctly measure the stresses on the engine parts and design them to endure, but engineers aren't perfect. The more power you squeeze out of an engine without increasing the displacement, the more stress it is under, and it becomes a question of how well it is designed. A manufacturer can probably safely take an engine (let's say a 4 cylinder) that was designed to make 180 hp, and bump it up to 205 or so without much re-engineering or problems. But if they try to get 350 out of that same engine without some re-design, they may start to impact reliability. That said, there are engines you can safely tune to that degree - it depends on the spec they were built to.

Now, the point. People want power, low vehicle prices, and fuel economy. So, car companies squeeze everything they can out of their small engines. Durability comes down to how well the engineers do their job, but a smaller engine making the same power as a bigger one will be under more stress - that's just physics. If I had a choice between a 6.0L V8 making 400hp and and 1.8L I4 making 400hp, I would expect the V8 to be more reliable. That doesn't mean it would always be true, though. The V8 could have been designed by idiots on a weekend and the I4 by geniuses over 20 years of racing experience.
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