So if easy on the throttle with a '87 6.9 with Banks turbo kit, 4x4, and auto what kind of freeway mileage should it be getting? Not sure of gearing.

Also would it be worth it to add on a OD or swap to an OD tranny?

 

Thats a pretty common question around here. The gearing will make a big difference, 3.55 gears can give up to 16 mpg, 4.10 and 10mpg is more likely. When I think freeway speed, I assume 70 mph, slower than that, and economy will be better.

Is is worth swapping an OD tranny? That is another comon question, but the answer is more complicated than the first one.

Adding a Gear Vendor's auxiliary overdrive is the most comon solution, but I went with a built up E4OD tranny.

A GV overdrive (or gear splitter) has a 20% overdrive and you will still have the slip of the torque converter to eat up some of your potential fuel economy.

An E4OD on the other hand, has a 29% overdrive and a locking torque converter, but in stock form its not as strong as a C6/GV combo and you will need to add a computer.

Both swaps are doable, and both will cost about the same, if we are to assume the E4OD is built up enough to match the C6. There are LOTS of upgrades avalable for the E4OD. and there are progamable computers avalable as well (I am running one).

If raw MPG is what your after, my vote is for an E4OD, but there are others who would disagree.

 

I understand the possible benefits of OD, and also the downside of a diesel being run at too high RPMs and out of its torque and efficiency curve. That being said - I used to want an OD trans for my 6.9 - but no longer think it's worth the effort. Here's why.

I have over forty diesel trucks - so I have lots to compare. I only keep four on the road at any given time, but I swap back and forth. In most cases, I've experienced very little difference in fuel mileage between my trucks with OD, and those without it. Maybe if all I did was highway cruising, it would be different. Every year, I take a 4000 mile trip with a pop-up slide-on truck camper, and I also do a fair amount of trailer towing. Having OD makes a big difference when it comes to noise and comfort -especially if you have 4.10 axles and have to drive 75 MPH. Fuel mileage however, I haven't seen much difference. My overdrive Ford diesel truck does a little worse than my non-overdrive Ford truck. A few examples:

My 85 F250 4WD Ex-cab, 6.9 diesel, 4.10 axles, and C6 trans. (no overdrive) - 4000 mile trip through Canada, New York, and the UP of Michigan with a truck-camper. Got 13.01 MPG average for the total trip. At home, empty truck at 65 MPH gets 12-13.5 MPG.

My 94 F250 4WD Ex-cab, 7.3 turbo diesel IDI, 4.10 axles and E40D trans. (with overdrive) - 4000 mile trip through Canada, New York, and the UP of Michigan with a truck-camper. Got 12.4 MPG average for the total trip. At home, empty truck at 65 MPH gets 12-14.5 MPG.

Also did some comparisons pulling a 21 foot camper trailer - same 4000 mile trip.

1983 Chevy Blazer 4WD 6.2 diesel, 3.08 axles and TH400 trans (no OD). 13.2 MPG for entire trip. Home highway mileage at 65 MPH is 20 MPG.

1986 Chevy Blazer 4WD 6.2 diesel, 3.08 axles and 700R4 trans (with OD).
13 MPG for the entire trip. Home highway mileage at 65 MPH is 21 MPG.

1989 GMC Suburban 4WD 3/4 ton, 6.2 diesel, 3.73 axles and TH400 trans (no OD). 13.5 MPG for entire trip. At home, empty highway mileage at 65 MPH is 18.5 MPG.

1992 Dodge 4WD 3/4 ton truck, 5.9 Cummins diesel, 3.55 axles, 5 speed manual trans with OD, 17 MPG for the entire trip. Empty at home on the highway at 65 MPH gets 20.5 MPG.

1982 Chevy K10 4WD 1/2 ton truck, 6.2 diesel, 3.08 axles, four speed manual trans with OD, 14 MPG for the entire trip. Empty at home gets 23 MPG highway at 65 MPH.

 

Thanks. It would just be nice if the OD swap didnt cost 3 grand. Im still looking for my first diesel to replace my old gas 4x4. Mainly just used for dump runs, camping, going to junkyard and a little fun on the trail. Maybe drive it more if the diesel can get decent mileage. Also my neighbor has a IDI truck and he is a diesel mechanic with all the cool tools. And with the diesel I want to pull a boat and be able to make the 350 mile trip to visit my cousin. I dont have much to spend, nor do I want to spend alot on a "work truck" and around where Im at I can find a decent non OD truck for $2-$3,000. while the ones with overdrive are over $5,000. My last truck a 73 Chevy 3/4 ton longbed cost $1500. Tho I dont drive it more than 50 miles at a time. And Im tired of not being able to pass a gas station without stopping.

 

In my case, I put a lot of high speed miles every year, so the payoff is actually there for me. But most of th etime it is not worth spending as much as the resale value of the whole truck in just one upgrade.

If you don't mind 2wd, then 3.08 gears become an option, with a manual transmission, you could get good results without breaking the bank. I'll admit I preffer auto, but if you want MPGs at the lowest cost, then a stick shift could be the answer for you.

Swapping out a 4sp manual for a 5speed is more cost effective than working around a C6 or E4OD. A good used ZF 5speed can be had for less than a grand in most cases, and better deals come up every now and then if you keep an eye out.