as stated i have an 85 3/4 with a 6.9 and a c-6 but im getting about 7-8 to a gallon... is that about right? or should i be getting more? it has 3.54's and posi in the rear if that counts for any thing

 

I have to hammer mine hard with rather big loads on the back to get that low.

I have a T 19 with 3.55"s in a dump bed 4x4 rig that weighs 8060 empty.
12 MPG is about my normal MPG with normal driving here in the mountains.

 

the t-19 is a 5 speed isnt it? i wish i had one id get so much better mileage

 

Nope. 4 speed with 1:1 ratio 4th gear.

 

Is somebody stealing your fuel?
I know a guy whos neighbor's son was stealing just a couple of gallons per day so he could keep getting away with it.
And this was back before gas/diesel went so high.

 

Just a suggestion but maybe you should try turning your pump back down. Maybe the previous owner already toyed with it.

 

The T 19 has the same final drive ratio as your C 6 does, but the C6 torque converter does not lock.

The engine RPM will be slightly higher with the C 6 because of this.

This is really an apple to oranges comparison though, turbo and other internal engine work compared to your NA engine.
I am also running a modified 7.3 turbo IP and DPS Stage 1 injectors, plenty of fuel and lots of boost to burn it all.

How much black smoke does it blow?

 

That's definitely too low. My 3/4, 6.9, C6 w/4.10 gets anywhere from 11-14 in town depending on how heavy I am with the right foot.

 

my calculations may be off then...

for the trip into school ( 33 miles ) i use an 1/8th of a tank at 50-55 on the front tank ( the back rusted in half at the seam ) i dont know how many gallons the front tank is, i have a chiltons manual but its for 80-86 fords ( all of them...) and it doesent have really any specifics

 

It's hard to calculate your ACTUAL mileage over so short of a run. There's a lot of room for error.

 

Using the gauge to guestimate MPG is not accurate at all.
When I want to check my MPG, I fill at the same station same pump parked in the same place when I fill up.
I also fill to the top of the filler spout every time I fill.

That way, after I average three or four tanks full, I have good numbers.

Your front tank should be 17 or 19 gallons, probably 19 with an extended cab.

19/8=2.3
33/2.3 = 14.3 MPG

 

consistantly ill use 1/8th of a tank there and back and when i get down to 1/4 tank ill put in 14 gallons + or - .5

 

So fill it up, get a receipt, write down the odometer reading on the receipt.
Now drive to school for 5 days.
Then go back to the same pump, fill it up, get a receipt, and write the odometer reading on it.

Odometer reading on the newest receipt, minus the reading on the oldest, then divide the answer by gallons on the second receipt and you have the MPG.

If you do this several times and average the MPG on each of them, you should have a rather good idea of what it is doing.



Since I use mine for business, I enter all my fuel purchases, repairs and maintenence in a spread sheet.
The spreadsheet calculates the MPG on every purchase.

If I see a sudden drop in MPG, unless I was working the truck hard on that tank I know something is wrong.
If there is no mechanical reason, then I know I have a leaking fuel cap.