No doubt about it. Dropping the ratio will improve your MPG
. Doing so (at the same road speed) cuts your engine RPM, thus your engine frictional HP.
I went from 3.73s to 3.08s and picked up 3 MPG
in my mixed city/suburban (35%), Interstate (30%) state roads (35%) driving loop. Actually its my 42 mile one-way commute. Why did i go to 3.08s? because i couldn't find any 2.73s.
I don't tow much but when I do, its dense but not draggy loads (10,000 lb
of shingles, 8,000 lb
of machinery, and the occasional Bobcat). Pulling 10,000 lb
of shingles through eastern KY (short steep hills) at night where I couldn't coast at all I got 15.5 MPG
. My all time best was 29 MPG
lightly loaded all Interstate.
One caution: If you have an automatic, I would not recommend going to less than 3.55. If you slow the engine down you also cut ATF
flow through the cooler and a cooked tranny can result. I had a GMC with the wimpy 6.2 and a TH400 but added a Gear Vendor overdrive. That rascal went through transmissions like a teenager through potato chips. Five dead TH400s. spectacular failures - parts and oil scattered down the road. i never thought i'd see the day when something would kill a TH400 but the low end gruunt of even a wimpy dioesel will do just that.
With a manual, no problem.
I intend to much lower but I need someone who can custom-hob hypoid gears for my sterling 10.25.