I am building a 66 F250 with a 77 460 this summer and is it too much dreaming to get decent mileage out of a 460. Here are the details of whats going in,rebuilt 460 with less then 20,000 miles that has a edelbrock performer intake with edelbrock carb along with a rebuilt C-6 and has a mallory unilite distributor which might come out since it does not have a vacumn advance. I have a 3.73 limited slip rear end that I am planning on changing to a 3.54 gear that will be going in and I am going to have full length headers and plan on tuning the carb,if I dont use the unilte distributor I will have a duraspark distributor recurved before putting in. The parts truck has a tach in it and when driving it home it was turning 2400 RPM at 70 with 3.73 gears,is 15 to 18 MPG empty too much dreaming. Jeff

 

Jeff,
I get 9.5 MPG with an 86 F250 4x4, 460 with a Performer & 4160 Holley tuned 622 jets 6.5 PV, Cloyes True Street Roller timing chain adv 4 degrees past TDC. dual 2.5" exhaust thru Summit Turbos. desmoged, with a C-6 with 3:55 gears on synthetic oil. I run stock 235/85/16 tires. On the road @ 65 MPH I might get 10.5 MPG.
IF YOU CAN GET 15-18 MPG out of a 460 I WANT TO KNOW HOW YOU DO IT AND I'M SURE EVERY PERSON ON THIS SITE WOULD LIKE TO KNOW. 13 MPG with an injected 460 has been talked about here, but real world I would question any better than that on any regular basis.

 

Some of the guys get 15mpg, but I think Barely.

I have a 94 F250 supercab 4WD 460 E4OD 4.10 long bed and I get pretty much 10-maybe 12mpg almost no matter how I drive. If I tow, I get 8-9 except in hills and headwinds.

I would guess with some lower number gears like 3.55? you have a better chance for decent mileage than I do with my 4.10's. Maybe the 66 F250 is a lot lighter than my truck which is about 7,500+ and it looks like you don't have the baggage of 4WD so maybe you have a chance.

This isn't an econobox engine and if you were able to get really good mileage I bet it looses the abilities that were designed into it. This is a truck motor for hauling loads.

Good Luck,

Jim Henderson

 

I had a feeling I might have been dreaming but I am going to try. Jeff

 

Jeff, the most important thing you can do to get that mileage up is to yank the C6 and put a 5 speed manual in it. It is possible to get 18 highway but everything has to be perfect, which can be tough to do in real life. The key is to get those RPM's and weight down. My 75 Supercab with new 460, all new accessories, 3.73 rear,timing at 14 BFTD, and NV4500 5 speed turns 1800 RPM at 60 mph and gets 18 mpg. The tires are 9.5/16.5. I hope you guys wont throw tomato's at me cause i didnt believe it at first either. Anyway, as things age I dont expect it to last. I run as light as possible-no spare tire or tool boxes. Most of us arnt on the highway 100% of the time so the 18 figure isnt that relavant anyway. Combined city highway is much less. I couldnt keep going with the 8 mpg I was getting with my C6. Im just posting this to say your dream is doable but the road to get there cost money. Look for a new article that will appear any day now on this issue.

 

You didn't say how tall the tires are on the donor truck but lets say they are 31 inches tall.
31*3.14=97.34 Tire Size
Drive Shaft RPM 2400/3.73=643.43 Axle Shaft RPM
643.73*97.34=62660.68 Distance Traveled In a Minute
62660.68*60=3759640.69 Distance Traveled In a Hour
3759640.69/12=313303.39 Distance in Feet In a Hour
313303.39/5280=59.33MPH

This is without tourqe convertor slip which is usually about 5-10 percent.
So your Tach or Speedodometor is off or you have 38 inch tires
Hope for 12-13
You will get better gas milage out of a 3 inch single exhaust.
I would have a custom built 2.5 inch y pipe dumping into a flowmaster y pipe collector finished off with a 70 series muffler
Use a duraspark dist with a MSD or my preference Crane HI-6 box straight off the magnetic pickup.
Jason

 

I have a '79 F-350 DRW 161" wb truck with a lightly modded 429. Driving the truck the way it was meant to be driven, I get 16.5mpg.

Some of this may be covered above, but...

The key's are...power, the motor must be built with power so you don't need the throttle. Minimum .65 hp per ci.

Another key is the tranny. The C6 is going to eat up some fuel, 3-4 mpg maybe, depending on how it's set up. I'm not an auto guy, so I'm not sure if or how it can be made more efficiently.

Another key is carburation. Keep it lean, yet safe. Vacuum secondaries set to open late helps too. Don't let the secondaries open up until you "need" them.

Modern radial tires like on the '80's and later trucks will help too. Don't skimp on the ply's get 8's for sure or even 10's, but don't get tires wider than needed. Too much unneeded friction. Also don't go more agressive on the tread than needed either. I put high traction tires on the 4x4's but highway tires on the 2wd's. I don't use my 4x4's unless I think there might be a need for 4wd. Like going to farm auctions where the area might be muddy or I have to park in a ditch.

True dual exhaust is good too. No need for fancy high tech mufflers unless you plan on racing. I run turbo mufflers and they work great. IMO, headers are not needed on a truck that will be driven conservatively on the street. No real need to rev the motor much over 3500rpm's, and headers don't really do much until about that rpm.

Now, when I say "meant to be driven", I mean like the manual say's. Keep your r's down, don't drive over 58-60mph, with 55 being better. These are older trucks, from an era when people, on average, drove at a slower pace. Even with overdrive, you don't gain a huge amount, or are able to drive faster, once you get into the low 60's for mph, wind resistance takes over, and starts to negate quite a bit of the gains overdrive will give you.

 

I got about 15 mpg in a '79 shortbox F-100 2wd with a swaped 460 C6.This was with 2.79 gears.This had a Performer intake and 650 carb.,headers and duals.I think the gears would have been better at 3.50s without hurting mpg.I never did better than 15/16mpg and sometimes got alot worse.

 

my best recorded HWY MPG is 14.5

-1990 F250
-460 EFI
-E40D
-3:55s
-stock cat with 3.5" catback straight pipe

Around town 9-10

 

Hey Jeff, you can do this. (A 460 economy truck.) In addition to a lot of the above recommendations:

Get "tri-Y'' headers. They are for torque, not high rpm and will be best for milage.

I don't even know if it is available for a 460, (somebody here will,) but see if you can get a spread bore intake manifold and run a Quadrajet carb. They have really small primary venturis and vacuum secondaries, which are huge. Those things will flow up to 750cfm, but if you drive on the small primaries your milage will be good.

And when you order your cam, keep the overlap to a minimum.

 

Lots of 460s from the 1970s had factory spread bore carbs.The common one is the Autolite/Motorcraft 4300 series carb.They do not have as big a difference between primaries and secondarie sides as a Quadrajet does .Not sure if you can get a Spreadbore aluminum manifold but Iron ones are common junkyard items.

 

my 27ft E350 motor home gets an honest 10mpg.
Thorley tri y headers, single 3" exhaust, excellorator muffler.
Edelbrock performer manifold, no EGR, no air pumps, Stock Carb. Fresh tune up.
3.54 gears, 215 85 16 tires.
C6 tranny. It weighs 11500lbs.
I drive at 55mph.

 

I get about 14 mpg in a 77 f250 4X4 (69/460) c6 4:10s with a pop-top camper on it if i keep my foot out of it. All stock but a 600 holley carb. Well guess in a 1969 460 you dont need to put the gas down to get it rolling.

 

I got 17.6 mpg once in my 1978 Marquis. It weighs 4880 empty...not much different from many 2wd trucks. It's got a C6, but the rearend is a 2.50. Bone stock (besides duals), 60 mph, cruise control, no a/c, maybe a full moon.

I don't thing 15 mpg will happen with your gears. I think the 5-speed idea is best, but then swap the rears to 3.08s. With an overdrive you'll be down to an effective 2.75 or so in 5th, and that would help.

My '97 F250HD is a 460 with 4.10s, 5-speed, 4wd, supercab. Drove it 1400 miles home after buying it. Got 11 mpg at 80 mph. Got closer to 14 at 65. Usually drove 80 anyhow, but that was all highway. Pulled off for fuel, and then more highway... and like the man said above, how often do we do that?

To get mpg, you need to get rid of rpms and wind resistance.

 

Rick1009 I like your setup, Change your duraspark Ignition box out with a crane HI-6 and a LX-92 Coil. If you put a volt meter on the red power wire going into the duraspark box it's under 7VDC. Imagine the spark output from a 7 volt system. Also buy a crane dist recurve kit.

Listen to rick's setup and his criuse RPM is about 2300 with toruqe convertor slip.

Jason