I'm going to try one more time to explain why a turbocharged engine works better in a tow vehicle. Say there is very steep hill of a known incline and a heavy rv also wit a known weight. Say the calculation is correctly done and it reveals that the HP required to go up the said hill with said rv at 20 mph is 400 HP at the crankshaft.
Let's say a turbo diesel is set up to put out 400 HP @ 2500 rpm and geared such that its 6 speed transmission will allow the truck to move 20 mph in 1st gear @ 2500 rpm....the truck is run up the hill and low and behold it does 20 mph.
If a gasser is set up to make 400 HP at 5000 rpm and has a rear axle ratio double that of the diesel it too will run up the hill at 20 mph.
When cruising down the highway at 70 mph the diesel will run in 6th at 1600 rpm where as the gasser will be running 3200 rpm.
Because 3200 rpm is too fast for a cruising rpm in even a gasoline engine it can be said that if the non turbo engine is going to compete with a turbo charged engine in a tow vehicle it will need more gears.
