fuel mileage

racerkyle · January 21, 2005

I know this is always brought up, but I have 1996 GMC Z-71 ext. cab. 350 vortec, I have a 6 inch lift and 35 inch mud terrain tires. I do have the Hypertech Programmer which is susposed to help out fuel mileage. But I need to know what I can do or buy to get more fuel mileage? I had a guy tell me he got 1.8 miles better per gallon in his car with the Tornado. What about that or throttle body spacers? I get about 12 mpg now, I drive town and country, not really Interstate! Thanks!

citydriver · January 21, 2005

That's a tough one, especially this time of the year with WINTER BLEND fuel.

I had fallen for the TORNADO BS and bought one for my truck(TBI unit)

and found that it was a waste of $$$$$$$$$

I did buy a throttle body spacer for under my TBI unit and it seemed to help in the mid-range torque dept....but I didnt notice much of an improvement in the milage, probably cause I could'nt keep my foot outa the accelerator

I'm assuming that you have had the SPEED SENSOR SIGNAL recallibrated for the larger tires (I beleive the Hypertech Programmer has that option)

But the added weight of the tires isn't helping any either....The gear ratio of the truck is ALSO a factor due to the larger rubber, this will cause the engine to work harder to get the truck moving....

Actually,IMHO, 12mpg is not bad given the circumstances...BUT I KNOW YOU DID NOT WANNA HEAR THAT!

There are others in this Forum that run 35s and have more similar set-up to yours,

I hope they can be of more help to you....I'm just being a postwhore sometimes

p.s. If you do a search on this site for the Tornado, you will find several other opinions on the subject

Yukon04 · January 21, 2005

The answer to your question lies in gearing. If you have the stock rearend in the truck, then there is the problem. With 35's, your gearing has been reduced and your engine/trans are effectively working harder for every rotation of the tire. You should change your gearing. Check out this link:

http://www.offroaders.com/info/tech-corner...ing/mph-rpm.htm

Gear changes are not as complicated as most people think. Take your time and buy the correct components and the job gets easier. The effective life of your driveline components will be increased with a correctly geared machine as well.

Good luck!