early ISX vs S60 vs C15 fuel economy

You need to be concerned with how it is maintained if it's cared for well either one can be a dog or a dream .....i.ve done great with a 12.7 I have done well with my current c15 though the gold paint on my parts is a little spendy

 

There's no question here. 12.7 all day long , they have always been the best on fuel out of all the engines.

 

detroit 60 is cheapest to buy,run and repair.

 

I'll take the N14 ..... Oh it wasn't on the list.

In that case, C15 all the way. The S60 is good on fuel , cheap to rebuild .. but too weak in the hills. A will built CAT, with correct rears and trans can get decent fuel mileage ... And will slaughter that Detroit in the hills.

 

Both the Detroit and Cat were well established engines. Ok, the C15 was new, but essentially it was a 3406. The ISX was an entirely new engine, and only was around for a year or two without EGR.

 

I'm willing to bet a minimum 1 mpg difference between a 12.7 and a E model cat. Minimum prob more.

My 14L gets about 1/2 mpg better then my 2WS doing same job same weight and same spec truck.
Oh and pulls every bit as good as the cat.
Both engines are tuned and putting well over 600 on the tires.