Following are excerpts from a thread on Sam's Marine (for Hatteras owners) which I originated... Thought this group would find the discussion of interest. Again I just read "turbos don't last as long as naturals" , but I disagree there is necessarily much, if any, difference. But there sure can be. Running both models hard will give the natural a longer life. But I doubt that's true if they are operated at about the same HP. Note also that this list concluded there is no discernable difference between fuel consumption when the engines are operated at the same HP. ("Turbo vs NA efficiency" thread.) If a natural aspirated engine is cruised at, say, 2000 RPM and a sister TI (same model, say 71 series engine) is also cruised at the same RPM, the natural is far more likely to last longer. That's because the turbo engine will be developing another, say, 20% or 25% more power than the natural at a given RPM. While the turbo boat should in theory being going faster so racking up less engine running time, I'd still give the clear edge to the natural for longevity. But let's change the comparison: Let's run both engines so they develop the same HP. As an approximate example, running a 325HP 8V71 at about 2000 RPM develops about 210 (propeller) HP. You can cruise a 8V71TI 435 HP engine at about 1800 and develop the same 210 (propeller) HP. My strong guess is that engines operated under these conditions will likely have comparable lives. (HP/RPM figures from DD power spec curves.) In addition, adding to the comparison wet risers on the naturals and safer dry risers on the turbos give some failure advantage to the turbos. Of course the turbos themselves are a maintenance item, but subjectively I'd guess (but have no hard evidence) that wet risers cause more failures than turbos...especially when the engines are run at moderate HP... Horsepower, Torque and RPM HP equals (torque in ft lbs x RPM)/ 5252.... So 600 ft lbs at 1800 RPM is (600 x 1800)5252 or about 205.6 HP, close to where we are talking. Working that backwards, 205.6 HP at 2,000 RPM requires 205.6(5252)/2000 or 540 ft lbs. Said a different way, to develop the same HP at a lower RPM, each piston stroke must produce more force(torque). The question becomes the tradeoff between increased force on the engine components with the fewer number of strokes taken. Fewer piston strokes developing a given HP must result from greater torque(force) per stroke...Does sound like a tradoff to an amateur...(me)... How does fuel consumption relate to this discussion? to overhaul time? We concluded that when developing the same HORSEPOWER, turbo and NA engines DO consume just about the same fuel...because fuel burn basically equates to HP At the same RPM the turbo engine will be developing more HP, in general, so will be burning more fuel than an NA....the boat should be going faster especially with the typically larger prop. For either engine, fuel burn is a general measure (and a good one) for rebuild estimates. It is better than just engine hours because fuel burn reflects not only run time but HP (RPM) developed. So an engine run at near WOT will burn a lot more fuel than one cruised at,say, 70% WOT. Because the turbo engine develops more HP at the same RPM, it burns more fuel at a given RPM and in theory requires rebuild sooner... There are only so many horsepower hours in any engine; you can take them out all at once or a little by little.