I'd love to have a crew and get 8-9......

But ya wow, that 14 is almost unbelievable. Wonder if it has anything to do with the matched intake and carb, or ignition upgrades? The C6 and 4.10's certainly can't help.... although with those tires, you actually get almost the same final ratio as me with 31's and 3.50's.

 

Hey guys. 1st post in a long time.

I get about 10mpg with my truck... not bad really. I think my mods will still be in my sig.

 

on your application with headers are you running what tube diameter and collector size?? most of the fenderwell headers i see are 1 5/8" tube and 3" collector. headman header. curious?

 

So far I'm up to about 9.5 at best ( up from 5.5 after my upgrades and tuning) Need to change the plugs and thinking an electric fan may help a little ( maybe to little to notice, input?) but, it's a 400 and since i have had the truck i have added a Holley 670, hei dizzy, 8.8 accel wires. it runs with 35/12.50's, and a 4 spd with 4.10 axle ratio. As for internals, po had a mild build done so not sure.

 

I get about 13-14mpg in my 79 f350 DRW 17 foot steel bed rollback. 400 4spd not sure of the rear gears has 7.50 16 tires.

i cant speak about exactly what is done to the motor.

when i bought it 2 years ago for 1000$ (it drove home) on inspection of the motor... it already had a weilan 4brl intake and edelbrock 4brl carb. stock Y pipe was cut and it had a true dual 2.5" comprised of turbo mufflers and 15 foot of flex pipe on each side lol...

I have since installed a HEI distributor,aluminum water pump,dbl roller timing set advanced 4 degrees,pair of 12" electric fans,2" carb spacer plate. did a full tuneup and carb rebuild. used a Gunson Colortune when setting the carb...plugs gap opened to .055

truck never sees over 4k rpm and it pulls hard

 

But those bigger tires are like bigger heavier flywheels than those little ones. Flywheels that have to be accelerated and slowed down.