Diesel vs gas......................
OK folks, there have been a few to many diesel vs gas threads that have shall we say gone to "Hell and a hand basket"! So if all of you would put in you BEST, no flaming reasons for going gas vs diese...
Forum Discussion
Ok lets compare the mentioned class 8 tractor with 365 horse to a pickup with 365 horsepower.
Horsepower is a function of torque and rpm. it is measurement of the amount of work that can be performed over time.
A road tractor with 365 horse would probably have it's hp peak at about 2100 rpm so for 365 horse at 2100 it would be making 913 ft lb of torque at 2100.
A gas pickup with 365 horse would have a hp peak at perhaps 5400 rpm. it would have 355 ft lb at 5400 to make 365 horse.
Torque is multiplied by the transmission. Let say for a road speed of 60 mph.
A 41 inch tall tire would have 492 revs per mile. so for 60 mph at 2100 rpm. a 3.55 rear end and a 1.20 transmission ratio. so 913 x 3.55 x 1.2 = 3889 x .768 = 2987 torque (what is .768? is the ratio of radius of 31.5 to 41 to account for the gearing difference of tires. 15.75/20.5 = .768)
A 31.5 inch high pickup tire has 640 revs per mile. so 5400 rpm with a 4.30 rear end and 1.96 tranny ratio. 355 x 4.3 x 1.96 = 2991
So the torque applied to the road from a gas pickup truck and a class 8 tractor with 365 horse is exactly the same. (they do vary a couple from rounding in ratios)
The difference is a class 8 tractor operating in a region with those kinds of hills probably has 18 speeds and tops out at 70. so it can be at it's horsepower peak ever 3.8 mph so for all intents in can always be at peak horsepower for towing applications. This is by design by the way.
A typical pickup truck is only at peak horsepower in two gears before 70 mph. So only at two road speeds is it ever at peak hp. A diesel pickup is no better. Put an 18 speed geared accordingly hooked to a gas 365 horse engine and it will tow every bit as well as the diesel road tractor. however it will use more fuel.
I have done the calcs for road torque between a lmm duramax and a new ford 6.2 and the ford gasser has more road torque at more road speeds in the 40-70 range than the diesel.
Horsepower is what matters.
Horsepower is a function of torque and rpm. it is measurement of the amount of work that can be performed over time.
A road tractor with 365 horse would probably have it's hp peak at about 2100 rpm so for 365 horse at 2100 it would be making 913 ft lb of torque at 2100.
A gas pickup with 365 horse would have a hp peak at perhaps 5400 rpm. it would have 355 ft lb at 5400 to make 365 horse.
Torque is multiplied by the transmission. Let say for a road speed of 60 mph.
A 41 inch tall tire would have 492 revs per mile. so for 60 mph at 2100 rpm. a 3.55 rear end and a 1.20 transmission ratio. so 913 x 3.55 x 1.2 = 3889 x .768 = 2987 torque (what is .768? is the ratio of radius of 31.5 to 41 to account for the gearing difference of tires. 15.75/20.5 = .768)
A 31.5 inch high pickup tire has 640 revs per mile. so 5400 rpm with a 4.30 rear end and 1.96 tranny ratio. 355 x 4.3 x 1.96 = 2991
So the torque applied to the road from a gas pickup truck and a class 8 tractor with 365 horse is exactly the same. (they do vary a couple from rounding in ratios)
The difference is a class 8 tractor operating in a region with those kinds of hills probably has 18 speeds and tops out at 70. so it can be at it's horsepower peak ever 3.8 mph so for all intents in can always be at peak horsepower for towing applications. This is by design by the way.
A typical pickup truck is only at peak horsepower in two gears before 70 mph. So only at two road speeds is it ever at peak hp. A diesel pickup is no better. Put an 18 speed geared accordingly hooked to a gas 365 horse engine and it will tow every bit as well as the diesel road tractor. however it will use more fuel.
I have done the calcs for road torque between a lmm duramax and a new ford 6.2 and the ford gasser has more road torque at more road speeds in the 40-70 range than the diesel.
Horsepower is what matters.
