The Stovebolt Site Forums The Parking Lot Big Bolts '72 GMC fuel milage

does anybody have an estimate on what kind of gas mileage my 72 GMC 7500 6X6 wrecker would get pulling a 28 foot semi trailer. it has the 401M 10 speed overdrive transmission and 7.10 axle ratio. also has a edlbrock 600 cfm carb.

I believe my '62 GMC 6500 with a 478 V-6 got about 7 or 8. The overdrive you have will help, but if you can get 8 that would be pretty good in my opinion.

Bill

I think 7 or 8 is wishful thinking. 5 is more realistic. If the 28 footer is a dry box 13'6" high expect about 4. Those old gas burners weren't very fuel efficient. I ran them until the late 60's. I run all diesels now.

yep it's a dry box

3.5 - 4 is what I'd expect. That's what an old glass truck I once had got with a 427.

A thought for ya, I had a '65 3/4-ton with a 327, TH350, & 5.30ish gears out back. When I got it the intake was all stock for that motor and it got horrible milage, somewhere around 5 or so. However, I broke down and bought a 650CFM 2-bbl Holley Pro-Jection TBI system and a Edelbrock performer intake. Between that, shorty headers with dual turbo mufflers & a swapped in HEI ignition, I went up to approx 10-15 MPG and could tweak it to run cleaner than a new car, plus had the ability to adjust on the fly (I mounted the brain in the glove-box. Before she died on me (head gasket leak, siezed piston, busted rod, oh darn,...) I was pulling a trailer and fully loaded bed and there was no real difference in fuel consumption.
I cant say what sort of performance gain YOU would get, but it's a thought.

I know it's heresy, puttin something so new fangled & confusing to work on on an old bolt, but then I'm one to be controversial. :P
However, if you're lookin to get the most bang for your buck,... It's an idea anyway.

i haven't seen any intake manifolds for the V6 but i do have rebuilt 427 tall deck that i could put in and run fuel injection with