Running empty @ 55mph, I gained 1-1.5 mpg (hilly area & 351w), but I think the gain would be more on towing.
There was a noticeable power gain though.......more proportionally, than the fuel saving.
A few months later I swapped the NP435 for a close ratio T19.
Night & day driving difference, due to both the ratios themselves, & the reduced gaps between - also a short-throw shift into 1st, unlike the T18 & NP435.
I've actually always wondered what driving in only front wheel drive would do to performance and mileage. You can do it if you twin stick the T case. With our knobby tires, and the crazy resistance these trucks put up to moving, ...etc...
NO difference, you'ld still be turning all the same parts and same tires carrying same loads with same flexing and same power needed.
Only by eliminating the turning of parts do you save, hence using 2 HI with unlocked hubs that then let front axles, front differential, front driveshaft stay still or just loaf along with minimal windage as some will do with thick grease in the transfer case. They do so at the equilibrium point where the windage of lube in the case spinning the gears creates enough force to turn the front drivetrain agaisnt frictional losses and the lube in the front differential.
Originally Posted by ford390gashog
If you are losing 500 to the converter then its bad!!! The more realistic number is about 230-320 rpms ( That is from Dave at Hughes ) consider one of their Fuel Miser conveters!! I really enjoy mine over the sloppy stock converter!! really brought the truck to life with the 1200 rpm stall and dropped the rpms at 55 mph about 200 !! Well worth the 220.00 cost of the unit and my trans temp is down over 20 degrees on the highway which is a huge help!!
Agree, 500 rpm loss to a factory convereter is way excessive at road speed. If what he's doing is power on and then power off and seeing a 500 rpm drop .... still seems high but near half of that change is in coast and is an rpm somewhat less than would show with a locked TC or clutch.
Fuel Miser converters huh? Might look into them myself when the 400 goes in.