[perky_intnl]

There are some pretty clever mechanical people out there. I have read some of there answers here in this forum.
I want to have somebody explain the differences in design between for example an inline 6 cylinder engine and a V6 or V8 engine, (or even V10). Ultimately I want tank tough, last forever durability & reliability.
Let me clarify why I want this explanation.
I have 1994 Dodge Ram with the 5.9 Cummins Diesel engine.
It is time to replace this truck, it has well over 400,000 kilometers, 250,000 miles.
I would love to have a truck with the Common Rail Direct Injection fuel pump system, however only the Duramax offers that, and I am not going to spend that kind of money for a late model nearly new truck.
So my options are the newer Dodge (either late 12V or early 24V) or the Power Stroke, approximately year 1998, 1999.
I am baffled at how the much smaller engine (the Cummins) can produce similar power and torque, and in many cases with better mileage, when compared with the Ford Power Stroke, which has approximately 20% more displacement. Even comparing the performance after everything possible has been done (Banks Turbo Kits, Mufflers, TLC etc) it seems that it is possible to get bigger performance boosts from the Cummins than the PowerStroke. So that seems to indicate some inherent strengths in the inline 6 design.
Now we get to the really grey areas for me, the difference in the Crankshaft length, and mass, moments of inertia, how many bearing are supporting it, does the extra mass contribute something to the torque potential, overhead valve designs.
I try and equate it with the old John Deere Single and 2 cylinder tractors that just chugged away but had a massive flywheel that allowed them to work forever.
There must be some influence from the increased surface area, ( The surface area, perimeter of rectangle will be larger than a square of the same surface area) possibly the distance that the various fluids (oil and coolant) have to travel etc, etc.

Ultimately this question will also apply to my next problem which is to try and determine whether I am better off with one 502 (8.2 liter) GM engine in my boat, or 2 Wankel rotary marine engines each producing 240 HP, and only 1.3 liters displacement each, and the two of them together weigh 300 lbs less than one 502.