Anybody over 12 mpg, put up what you're getting, as many details of your truck as you can, and anything else you think has a major influence.

I was at juuust under 10 with a C6, tired converter, and 9.2 compression. I'm now putting in a 4 spd, and hoping to gain 2, and raising compression to 10.7, hoping to gain another one.

I really believe decent, normal big block, big truck mileage, with excellent performance is possible on these engines, I'm just not sure where it's hiding, and what's holding us back. I wanna stay carbed, that's a big part of the feel of these trucks and engines for me, AND I WANT 16 MPG!

Let's see if we can get one above twelve for starters..... AleX

 

13mpg.- 93 octane
351M/408, 9.34:1 compression(TMeyer pistons), O.E.M. heads, Scorpion rollers, CompCam 255DEH, Edelbrock Performer 400 intake, Edelbrock 1406 Carb, 1 5/8" headers w/2.5" dual exhaust and turbo mufflers, Re-curved Motorcraft Distributor, C6 trans, 2wd, 3.25:1 rear, Aluminum wheels w/255-70-15 tires.
I don't believe we'll every see 16mpg's with these old trucks, not with carburated 335 or 385 series engine. Maybe with computerized fuel injected?

 

In 1989 I and the wife and our dog took a road trip in the '77 with 351M, C-6, 3.50 gears, 31" tires, Edelbrock intake, the current Crane Fireball cam, dual exh, and a Holley 1850 600 CFM carb and new plugs and wires and a vacume gage mounted beside the tach ... and it had a fibreglass shell and we camped using that. Drove down through Smokies and over to Raliegh and down near Ga through South Carolina and then up the coast through Outer Banks, up Eastern Shore into De., across Md to West Va, taking in all the sights.

I took my timing light, some jets, a couple power valves, and spent some time at fuel stops tuning occasionally looking for changes in MPG. 12-14 was the best I got and it still running smooth, I got it a bit too lean there on the way home .... burnt a valve and eneded up getting head work done. Went back to a richer setup on the PV and main jets, heads have lived, mileage is 12-13.

I think over the years, it's dropped some, but seems better with the Edelbrock 600 cfm carb (and Holley regulator at 5.5 psi) now, certainly no leaks all over the intake.

 

hughes makes a nice torque converter for your c-6, make sure your cam works with your torque converter!!!!!! 4speed issues, your oil in tranny causes resistance and drag. my big block on 38" skinny tires gets 12mpg and some c-6 upgrades. rolling resistance tire pressure and weight of truck. good tune on engine. Also a modern carb with some nice tuning features really help on the tune. multistrike igniton helps. currently building a 400 ford and doing someupgrades to truck to see if I can get the elusive 16mpg?? don't know if possible but taking a shot at it with a carbed engine. I spent a lot of money on carb to do what I want. didn't run a edelbrock!!! your engine oils weight really change the engine and efficiency.heavier the weight more the drag, but be careful on your application. if heavier oils is required for application do it. carbs learn about annular boosters in carbs. quick fuel tech site has excellent info on this subject annular boosters. also pro systems has some good reading also. AED carbs has some good stuff. lead a horse to water but can't make him drink it. knowledge is power!

 

what size headers do you run and collectors? what cam and spec's?:- headers by ED has some pretty good reading on torque and power and application. learn on his 30 plus yrs of experience. has a disc to listen to while driveing and lots of reading if you buy his packet. definelty worth the time to read. knowledge is power.

 

If you are taking the time to do a C6 to 4 speed and you are aiming for good mileage why not just go strait to the ZF5. OD has got to help (or at least couldn’t hurt) mileage. I get 12mpg in my 1979 f350 supercab (C6, 400, 4x4, 3.50, 235/80r16 and completely stock) and am hoping to go to a ZF soon.

 

yea a zf is another option. but their is some mild fab work to be done. currently doing this as wee speak.

 

I'm trying to figure out a way to get the fuel to atomize better below the carb. That's one of the huge places fuel injection gets it's better mileage from.

Anyway though, I didn't do a ZF because of the cost, and because I've heard of guys blowing out the O/D fairly easily. I am hoping to do some kind of overdrive sometime soon, but it's not in the budget at the moment, just that simple.

As far as headers, I'm running some mid range long tube Hookers. 1-3/4" primaries, 3" collectors, into 2-1/4" true duals with very low restriction mufflers. I'll read up on that headers by ED thing if I can find it, I'm very interested in the scientific side of all this.

I'm just running a stock converter (though none anymore), and I knew it wasn't necessarily ideal, but for the money, and with swapping to a manual sometime soon in mind, I just didn't justify an upgrade.

I also have a stock cam in at the moment. I did this once again, for the money (free), but also very much to gain a full pressure stroke (both valves closed) for as much of the stroke as possible.

I will soon be upgrading to dome top pistons, from my current flats, and a much longer duration, somewhat taller cam. I've run the cam before with much lower compression (stock dish tops) and I even loved it then, so I'm hoping the new build will be beautiful. It just felt right, with the headers and intake combo. I've done the math and it shouldn't ping, but we'll have to see. I'm also hoping the compression bump will help my efficiency, as it in theory should.

 

well on the fuel going from a liquid to a vapor. this starts in the carb! some boosters are by design better than others in 4wd application. learn about annular boosters and low rpm application. quick fuel has a tech section on this that might interest you. I've been running these for many yrs and seems to be the way to go for our application. i speak of these often in 4wd application and very few listen and throw a edelbrock on. edelbrock decent carb but if wanting to push the envelope get educated and annulars for 4wds/low rpms.

 

My mileage isn't what anyone would call good or decent even. I get 8 mpg with a 400(flat top pistons, .520 exhaust/.480? intake cam), Holley 500 cfm 2 brrl carb, the a/c pulley and belt removed, c6, 2.75 gears in the rear with 12x9.5-15 size tires. And I have a lead foot.

 

I got two trucks with 400s. My wheelin rig, 400 bored .030" stock compresion, comp camps 268 cams, edelbrock springs, double timing chain, edelbrock intake and carb and open headers. It gets around 8-9mpg. also running a 4spd and 4.10s with 38s.

My daily is a 400 bored .030" stock compresion, edelbrock intake, carb. msd 6a, msd billet distributor, headers and 2.5" exhaust c6 auto 37s and 4.10s i get about 14mpg with it. Its also a crewcab short box 4wd lifted 6" and im happy with the mpg i get. Ive taken several road trips, to alaska and back towing a trailer and average 12mpg.

My wheelin truck, has TONS of torque. with the cam it kinda falls off after about 4500rpm, but wow the low end power is crazy. I can stab the pedal doing 30 and spin 38s on dry pavement with it. The daily driver, really pulls on the highway, it will bury the speedo and then some. the power around town isnt bad but it feels like its got a bit more top end power.

I used the crew cab for a daily and tow rig and the power and mileage is great cant complain at all!

 

One of my freind sandblast the inside of the intake manifold(aluminium). He said it help atomization, better hp,tq and fuel millage.

 

Well, I once made 15 with a f350 4x4 4spd reg cab 354 gears non ac small fan, fresh stock rebuild, single exhaust, timed by ear, edelbrock intake and 600 carb leaned down, and I did it once.

The 354s help immensely over 410s and the 4 spd seems to give you 10% or so over an auto.

I bought a truck from a retired driller that used 77-79 f150 and f250s for his fleet trucks for years. He said the 351 made 14-15 consistently on the highway, occasionally 16 and the 400 made 11-12 consistently on the highway. He ran 4 spds and no ac but all stock.

 

Wow, be careful with that, even a couple grains of sand not cleaned out, make for a bad day.

 

Holy Crap on the 14 mpg with the crew!!!! Mine is bone stock and getting about 8-9. Does the Edel carb make that big a diff? Do you have an electric fan? I would love to get even close to 14.