My 460 is getting about 7 MPG. It does have a weak valve spring that i will be repairing shortly. I dont see black smoke out exhaust... Is 7 MPG highway common for 460's? Or could it be due to the weak valave spring? 7 MPG is horrible!!!

-This post asked two questions and started two conversations that were split into two threads. The original thread was: https://www.ford-trucks.com/forums/s...hreadid=117142

 

I am having the same problem on my F350, still working on it.
This could be a number of large or small things, but I recommend trying the smaller things first, it can make a difference.
First of all, on my truck, the curb idle was lean, then rich, so I adjusted it and got 7mpg out of it. Then, later on, I changed out the carb to an Edelbrock, gave it more power, but only put out 7.3 average. Then I took apart the carb, adjusted the bowls, ran some new fuel line, checked the filter, which all helped a little. Now I noticed that my pump squirt into the venturi is weak, so I am replacing the fuel pump next week. So have fun.

 

You mean the accelerator pump?

 

Accelerator pump? No, I already worked on enlarging the accelerator pump stroke if thats what you mean. I have already done all of the other work with the filters and all that, and I am convinced its the pump because too many things are pointing in that direction.

 

A friend of mine has a 460 out of a car in a 1979 F-250 with 3.52 gears, 33 inch tires and the manual 4sp. he gets 12 MPG loaded or empty.

(he drives on the freeway a lot)

 

Have you tested pump delivery pressure and volume?

When you said the pump squirts looked weak that is one of two things:
-bad accelerator pump.
-very low to no fuel in the bowl.

12 mpg is more normal but "loaded or empty" means the gears are not right. Sounds like a candidate for an OD unit or some 3.07 gears like mine. With a 460 he could probably push a ~2.5 gear down the road. Some of those old big Lincolns did that.

 

You said that one 460 came out of car, and gets 12mpg right? Would that mean that the engine has a higher compression ratio than a truck 460? Because I heard that the comp ratio can give better fuel economy and 12mpg is very good for a 460 (in my experience). What did you mean when you said that a flat 12mpg means the gears are going out?

 

Colossus- Read the post again, I didn't say anything about gears going out.

 

I'm sorry I read that wrong. My bad.

 

Thanks for the input. I checked the accelerator pump and its linkage, and no problem with it, it was set at maximum, problem might be lack of fuel into carb - but as long as there is fuel it pumps real good.

 

There is just not much that can be done to improve the mileage on a 460 V8. I have tried headers & duals, and changing the induction system and it might of gone from 10 to 11 MPG. Maybe?

The 460 is just not an economical motor no matter what is done to it. I've tried!

 

It can be geared to take advantage of the torque it puts out. If you are unwilling to gear it correctly and use the correct transmission gears when towing it will suck gas. If you insist upon gearing the engine to tow 8000# in the mountains in high gear it WILL suck gas when you drive it around town empty. Just simple physics which most users ignore.

 

Ok Torque1st - everything you have said makes complete sense about gearing. What gearing would be the best for general driving, towing, and most importantly - which gearing would be best for general use? Thanks...

 

Find yourself a diff, OD, and tires to keep the cruise rpm's down around 1200-1500. Some sort of overdrive will be required. If you use an overdrive tranny or gear splitter unit then you can downshift as required to pull your load up a hill. Just like the big rigs do. You don't see a tractor pulling a trailer in it's highest gear up a hill.

You will need to have the proper camshaft in the engine for max low end torque also. Factory stock big Lincoln cams are good. Gearing a built 460 with a 280 cam won't work either. The entire system must be a matched unit. The factory spends big bucks on R&D to get everything matched up right.

 

Original topic split into two threads. See first post.