Mileage improvement C6 to T19/ZF5/ZF6? +4sp to 5 sp improvements

[masterbeavis]

Another newb question, I am sorry, I cant help it. For those of you who had a C6 and swapped either to a T19, or a ZF, what kind of fuel mileage changes did you notice afterwards? If you went from a 4 speed, to a 5 speed, what kind of difference, aside from being able to go faster on the freeway, did you notice? Is life with a 6 speed any easier in the hills towing?

The C6 in my truck is fried. I plan on patching it up for now, but in the future, I plan on dumping it in lieu of a stickshift. I can get the T19 and related stuff for $250 or so, but the ZF is going to cost me significantly more(trans and fancy flywheel). In CA, the speedlimit with a trailer is 55 MPH, so being able to fly down the highway with a trailer is not really needed, unless I want a speeding ticket. I do not plan on daily driving this truck, that is what my VW truck is for (at 40-50 MPG).

Thoughts/personal experience?

 

[Diesel JD]

T19...I'll tell you when I do my swap about the mileage improvement, but just judging by those who have the T19 and 3.55 gears its usually 15-17mpg empty for them but for me its 12-14 in town empty with a C6. Now Jake S may or may not post but I recall he swapped from the C6 to a ZF5 and he went from 12-12.5 with the C6 to 17mpg.

 

[masterbeavis]

T19...I'll tell you when I do my swap about the mileage improvement, but just judging by those who have the T19 and 3.55 gears its usually 15-17mpg empty for them but for me its 12-14 in town empty with a C6. Now Jake S may or may not post but I recall he swapped from the C6 to a ZF5 and he went from 12-12.5 with the C6 to 17mpg.

I was told by the PO, the truck got 16-17MPG empty. (I cannot drive the truck yet to confirm) I can only hope it gets better.

 

[Diesel JD]

I will believe that a C6 F250 will get 16-17 mpg empty but it would have to be at highway speeds and no more than 60-65mph depending on which gearset you have. I've gotten a few good tanks like that with mine. If its not a DD isn't that pretty good for a truck that runs 4500lbs plus before you put the first thing on it? Granted, not as good as many old cummins or GM 6.2s but pretty good nonetheless. It seems these things vary at random in terms of what they can achieve. Mine seems a bit on the low side of the fuel economy range and the guy that claimed 22mpg I have no reason to doubt him, its just on the high side. My best guess is thay with a T19 you'd pick up a mpg or two and an OD like a DNE2 or perhaps a ZF5 would be good for another mpg or two or three beyond that.

 

[HammerDown]

I will believe that a C6 F250 will get 16-17 mpg empty but it would have to be at highway speeds and no more than 60-65mph depending on which gearset you have...

True...w/355 gears my F250 4x4 held at 60-65 (not towing) as got 19.8 mpg but...it takes time to stretch it's legs to see that number.

 

[freebird01]

True...w/355 gears my F250 4x4 held at 60-65 (not towing) as got 19.8 mpg but...it takes time to stretch it's legs to see that number.

how can you manage that in PA?....my truck is an 88 F250 w/ 3.55's and a ZF5 and a banks turbo and even if i drive like a grandma ( easy pull outs and stops light on the pedal) the BEST i ever got was 17.2 on my last tank of #2 using amsoil diesel additive instead of the normal 2cyl oil i use...

and my truck only has 92,000.... is that straight highway running?

 

[The Warden]

I can't comment definitively on mileage comparisons after swapping from a C6, but I gained 4 or 5 mpg when I switched my T-19 for a ZF. After the turbo swap, I was getting about 12 mpg with the T-19 (MAYBE 14 on a long freeway run)...after the tranny swap, I'm seeing 16 to 18, and I broke the 20 mark on a freeway run a couple of times. This is with a non-gated ATS turbo, 4.10 gears, and stock tires.

FWIW, I was seeing 14 mpg in my old E-350 with 3.54's and oversize tires...

 

[Diesel JD]

Of course the van had a C6 w/ 3.54, my C6 with 3.55s gets the 12-14mpg range or a bit more on the highway at <65mph. The C6 sucks up a lot of power folks, its a great tranny but not competitive in an era of high diesel/gas prices. The T19 does not suck up nearly so much power but falls on its face for lack of overdrive. I've heard good reports with t19 and 3.54/55 gears, I only hope my luck will be as good, or if I'm lucky or patient swapping in a cheaper, used overdrive of some sort, I know I can get in the range of 20mpg on the highway and 15-16+ in town with the T19. Since the originla poster does not intend to make the 250 his DD fuel prices and MPG are less of a concern, and with limiting himself to 55mph pulling the no OD will be a small issue. I recommend a T18/19. Why cause its cheap, tough and not a highly specialized tranny to build should the need arise.

 

[masterbeavis]

I do not intend on making my truck a DD, that is true, however there will be times when I need to drive it to work, which would be *nice* if I was getting good fuel economy.. A ZF would really be nice, but I cannot seem to find one in good shape that is cheap enough for me to afford (

 

[Jake S.]

True I was getting 12.5-13 before the swap and about 17 after. I believe that a diesel has low end for a reason and you cannot use it with a C6. So that is where most of my gains came from. With the C6 I never saw below 2000 rpms. Now that is about the highest I go, unless loaded.