I had a 94 12valve about 8 years ago. The truck had around 450-500 hp. And it would get 20mpg in town and the highway. It had 33x12.50 tires too. Hx40, 4" straight pipe, bhaf, marine injectors, aftermarket cam, and timing set at 25. All this was done by the previous owner. The best I've seen so far with the truck I have right now is 17. I think the 94 also had 4:10's. I've read people saying the see 25 mpg. How do they accomplish that?

 

I have a 96 12v with 4:10s not modded much 4" straight out the back and 3gsk that doesnt get much use and some little stuff. Im running 37" tires so i cruise at 1500rpm doing around 65 and if my fuel gauge is accurate at all i get at least 25mpg. the other day i did 100 freeway miles on an eighth a tank if im right about the tank being 28 gallons thats just over 28mpg

 

So your getting 700 miles out of a full tank?

 

Is your tank not a 35 gallon? I always figure mileage by filling up and toping off the tank, setting the trip to 0, and then driving. I check the accuracy of the trip meter with a GPS, (it may not be off the same as the speedo for tires/gears/etc) and figure out how many miles I've actually travelled when I stop for fuel. Then I fill it up/top it off again and divide the miles by the gallons. If your getting 28mpg (I doubt it) then we'd all like to hear more about 'some small stuff' mods you've done to your truck! You cannot use the movement of the fuel gauge to guess at how many gallons you've used. For example, my truck will go 200 miles one the first 1/4 tank but then only about 125miles per 1/4 tank after that. I know by looking at my trucks fuel gauge if it's going to be good or not based on how much I've seen it move per 1/4 tank over several fuel tanks. But I can't do an estimate on how many gallons are used.

 

I'm am interested to see what others are doing to improve there mpg, I am in the process of "detuning" my truck for this goal. Currently averaging 13.5. (A lot of motor+suck *** turbo
=13.5 mpg) to my surprise I singled my duals and seen no real change!! Maybe .5 mpg. I am planning smaller injectors, maybe 7x.011? And a tow twin setup with a modded hx35 and my s366.

 

Well for starters, I removed my fan for the winter!!!
I also got some rubber mat that I'm going to cut for an air dam up front that will have some 'give' in it for obstacle clearance. Timing in the 15-16 deg range seems to work for mpg. I'd be a little careful about 'detuning' it too much. Many times a more powerful motor driven like an old lady will return better mpg than a weaker motor. 5 x 16's do sound like more than you want for fuel mileage though.

 

LOL 28mpg, 37 inch tires and an uncorrected speedo and Odometer of course you are getting 28mpg. i barely get that out of my geo tracker with a 1.6L LOL

a stock 245/75/16 revolutions per mile = 662.3
a 33 in tall tire = 611.5
a 37 in tire = 545.4
a 44 in tire = 458.6

um... which one spins slower and retards the reading of your speedo and odometer more? come on guys. the taller a truck is the worse aerodynamics it has the bigger tires are heavier all add up to dramatically reduced fuel economy.

so from a stock tire to a 37 inch tire is an 18% reduction in revolutions per mile
so if you are getting 28mpg x 82% = you get 22.96mpg mathematically not including the loss of power use to get the heavier less efficient thing going. 23mpg is still and INCREDIBLE number for a 2nd gen 12 valve and i still throw the BS flag to it but is closer to believable. if you have a 4x4 2nd gen on bigger tires consider yourself very very blessed to be getting between 18-20 empty the other 98ish% of us are satisfied enough with 16 empty and 10-12ish pulling a trailer.

to make it get better fuel mileage drop it to the ground run it on skinny street tires rip all the unnecessary things off of it making it lighter and drive it like your grandma on flat roads @ around 70* empty

LOL 28mpg

also to correct for tire size and gear change all you need is the correct size $35 speedo gear, it is one bolt to remove it and a good tug and push the new one in the holder.

 

Turbo if I read your post correctly I think you did the math backwards. If he has larger tires he is turning less revolutions per mile, but his speedo doesn't know that. So he is actually traveling further than his trip meter says getting better than 28mpg!
Ok, not really.
But I have found that using taller skinner tires I've gotten better mpg in every vehicle I've owned than with stock size, obviously there is a point of no/diminishing returns and if I could have changed gear ratios and used smaller tires that would also have worked.