trade off

[kunsan1987]

This may be a good thread to start the MPG tweaking!


i could use some pointers in this direction!

[EagleMark]

All the tweaking won't help that beast in your avatar!

Seriously the bigger the tire the worse the fuel milage, the heavier the tire and wheel the worse the MPG. It takes HP just to turn the weight of wheel and tire before moving the weight of vehicle. HP takes fuel!

The best increase in MPG is a block of wood under the skinny pedal! I like to go fast and with a size 16 foot, the block of wood was my best increase... then the tweaking.

[kunsan1987]

yes i took the weights out of my right boot.my 83 pickup has 4.10 gears great for towing not so good for mileage.
i am getting about 11 mpg,5.7l th400 np208.
i have my ve dialed in i believe and i'm now working on my spark.

[ony]

eagle mark did your suburbun come with 373 gears, i put a 341 in my truck today now my speedometer is way fast. i have stock tires it is suppose to have a 308 had a 273, changing it fixed 2 problems and created 2 more. fast speedometer an oldometer, i was wondering if there is a easy fix that you might know of.

[kunsan1987]

ony try this site the have some speedo gears and a calculator to figure out the proper drive or driven gear for your setup.

http://www.transmissioncenter.net/sp...n_______va.htm

[EagleMark]

Actually it's got to be done in the DRAC on his or VSSB on newer PCM.

Yeah my old Suburban came with 3:73. Was thinking lower gears would get me more MPG but I don't go that far and it drives nice with them.

[ony]

idint know if you had to change any thing or not, i found a web page on recalibrating a drac, but for the life of me i cannot find the white box, tbi.com. i took my speedometer apart didnot see any thing in there that looked like a drac, i run vin numbers on different websites it is a 91 c1500, the odometer and speed odometer being off seams to be messing with my program at idel. it was real smooth when comming to a stop,now 2 out of 3 stops it runs a little rough, i think the change in gear ratio is confusing the ecm. i cannot fix the odometer being fast, if i can get my camera to work you will laugh you ass off for the speedometer fix,.

[EagleMark]

I never changed gears, it's to good as is.

It could be affecting idle because of paremeter "IAC - MPH Threshold for Idle" now that MPH has changed, but I doubt it?

Your 91 probably has the DRAC in speedometer, real PIA... We have the info here somewhere but this link has pictures. Not sure how to fix them as the parts aren't available anymore. White DRAC box is easy to change. Not sure how to do the one in speedon without parts? 1project2many may know?
http://67-72chevytrucks.com/vboard/s...d.php?t=313815

[ony]

if i can find where the speedometer an oldometer is feed dc in the insutment cluster board might be able to short some dc to ground to make up for the difference for being feed to much pulse, using a potemeter {ajustable resistor pod}.

[ony]

found a artical on chevytalk.org i look at his chart an clipped #4 fuse in the speedometer board #6 was already blowed, may work out ok, getting ready to try it out if i can get out of the kitchen. idont know why 341 is stuck in my head, its a 342 rear axle.

[ony]

that is a good artical, chevytalk.org/calibrating 1988 1991 speedometers. i put the little switch in the speedometer board it calibrated as a 373 with 235 tires on it which is what i got. the man told me it was a 373 but the glove box showed gu6. trying to get mileage, 2 weeks ago odometer stoped working finaly found a 91 that would work, monday rear end failed fixed it speedometer odometer way off. its close now acroding to gps can go back to tunning. if you are having speedo trouble check out that article it worked for me {i dont have a drac box it is in the speedo board}

[EagleMark]

Here's the article link:
http://www.chevytalk.org/fusionbb/sh...hp?tid/258562/

But some 87 to 91 do have a DRAC! My 90 Suburban does, I think it is because of anti lock rear brakes.

[ony]

mine dont, it is all in the speedometer board on my truck, i have abs but this truck is a one year deal. liked to never found a speedometer that would work. i would put one in the truck would not run, pull it out it would run fine without the insterment cluster it was assembled in canada acroding to the vin#. the lttle motor went bad is why the oldometer stop. mine is a std trans