The C7 is 7.2 liter or 441 cu in
The C15 is 15.2 liter or 928 cu in
My C15 is set to 475hp 1650 ft lb torque. A 300 hp C7 has max 860 ft lbs torque.
Notice that even though hp is up approx 50%, the torque is double. Torque takes you up the hill.
My Century Freightliner @55,000 lbs total weight pulls a 8.5% grade easily at 60mph and didn't overheat in the summer months.
Fuel mileage is around 8.5 to 9mpg on the highway which I find acceptable for this much engine. Some say mileage will go up with a few more miles on it but to date it has 27000.
May look at "chipping it" down the road.
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