4x4ord wrote:
I guess we agree then.
When you look at the BSFC map that you posted you can see that the rpm and load you selected are for one very specific circumstance. If you start pulling a little harder the transmission is going to automatically shift down a gear. If you start pulling slightly lighter you will be getting better fuel economy in the higher gear. Towing a trailer down the road is a constantly changing load so the actual load might seldom be at the average. Even if you have a BSFC map for your engine, unless you are constantly watching your instantaneous fuel consumption and are able to calculate in your head how your mpg converts to engine torque and rpm, you will have an impossible task of knowing which gear is most fuel efficient. I'm saying it is best to keep it simple and just let "Drive" with "tow haul" do the thinking for you. The basic principle is throttle down and gear up for better fuel economy. If we find ourselves on a road where the transmission is constantly up shifting only to end up in too high of gear where it needs to recover with a downshift then I know we would agree it's time to lock out 6th.
I was able to find out which gear was most efficient without a map by using the averages of multiple trips of pulling my trailer to the coast at 6th gear and 5th. It really wasn't that hard to do and if I would had let the transmission do all the work then I would be getting less fuel economy even in tow/haul mode.
My father in law will be testing this theory in his 2019 F350 Fx4 3.55 in the coming weeks. He will tow four 20 ft shipping containers one at a time back and forth from out deer lease(130 miles). He said he was going to try towing two with 6th unlocked and 2 with 6th locked out.
Below where my truck would be at towing my 13k 5ver. Up/down is the amount of torque needed for each grade and right/left is rpm at each speed. Yellow is 6th gear and red is 5th. There are definitely certain speeds(especially 60-65 mph) and loads when my truck is more efficient in 5th than 6th. Of course these torque requirements are based on weight and do not calculate for a lot of drag so I likely need more torque pulling my 5ver at each grade.
