[Buellwinkle]

Engines are likely made to a durability spec, so if a manufacturer makes 4 different motors, the engineers that designed those engines were probably given a spec, make those engines last X number of miles. So they design the components and use materials as such to acheive their engineering goal. So one would think that say a V8 in the same car that can also have a I4 would last longer because it's not working as hard and many of us have seen cases where engines last an extrodinary amount of miles (had a buddy drove 95 miles each way to work in a 4 cylinder Pontiac Grand Am, laid it to rest with 300K miles). I know the M271 is a very poor design, probably designed in the middle of Oktoberfest by a team of drunk German's, but that has nothing to do with the intent of the question which I took it to mean, is a larger engine inherently more reliable than a smaller engine that's asked to do the same work and I think not.

 

[Buellwinkle]

Still, the 200 HP motor is likely made knowing that it will be run harder than the 500 HP motor, so size is not a factor in how long a motor will last. The strains on the rest of the car would be greater with a 500 HP motor, given the same car. For example, I believe MB uses the same transmission in the C240 and C32 of the same year, so you have to figure that the stresses on the drivetrain with double the power would be greater with a C32 (assuming he bought a C32 because he wants to drive it harder). Also, to achieve double the HP using the same block must have it's challenges.

 

[Buellwinkle]

Still, you assume that two similar engines of different displacements but same HP are built the same and I doubt that. If you take a smaller engine and you yourself adds HP through aftermarket component, then yes, it will not last as long as the bigger engine because you didn't upgrade internal bits to make it last under the additional load.

 

[Buellwinkle]

Surprisingly, a pulley kit won't shorten life that much because the car is rarely under any boost unless you floor it. I would bet that the amount of time your car is under boost in normal driving is less than 1%. Then you are only overdriving the s/c at near redline, probably not all that common in everyday driving.

146K w/ ASP pulley and still running strong. Should I be worried?