I'll be interested to see what mine does... haven't done more than initial break in run... from what I remember, one of the problems with the 460 was exhaust flow... affecting both performance and mileage.

I did some serious exhaust port smoothing, taking out the thermactor hump and radiusing the exit ramp for a smoother flow..

so with a mild cam, edlebrock performer intake and a 650 Quick Fuel carb tuned well, I'm hoping for 10-12... if that magnetic floor doesn't keep my foot glued down to it.

I knew going with a 460 that I couldn't challenge a Prius for MPG... well actually when I started this project... the Prius wasn't even on the drawing board. A hybrid was a corn or tomato variety !!

later
John

 

What's the point in having a big motor if you try to gear it down...........

 

Best done with an overdrive.

 

My 56 panel with a 460 has a moderate performance build to about 450-500 hp. ( I include that just for comparison to stock). With me in it (190), it weighs 4120 lbs.
C6 tranny with
3.50 posi = about 10.5 mpg.
2.75 open = 14 mph on hwy.
I agree with fat fenders and others; spend money on overdrive. The 2.75 goes against everything about my engine build. Of course it will drive fine as a cruiser, but then so will a stock 300 or 302. I put the 2.75s in for the Power Tour, 3500 mile round trip; a great poor man's overdrive and was very happy. Since it's not a daily driver, I keep the 3.50s in, engine is happier around town. Even the guys with factory efi on these pigs are getting crappy mileage, that's what ultimately kept me from spending 2K on efi. Gear vendors is 3K, so I'll just swap out gears every time I do a Power Tour. Btw, that 10.5 mpg is only going 55-60 mph on hwy😂. ..gotta go for smiles per mile with a 460

 

Make sure that you use Holley's carb selector tool:
https://www.holley.com/products/fuel...s/carburetors/

Most people make the mistake of over carbureting their engines. Bigger is not better, just thirstier with less performance particularly at low end and high altitudes.

Getting a carb with an electric choke will help as it will be more efficient than a hand choke on cold starts.

Don't overlook the fact that headers will help also.

Then ask yourself what is it really going to cost you in extra fuel. You can spend a lot of money and basically see no savings (i.e. the cost of the extra fuel does not offset the cost of the parts).

 

Just more testimony to a humongous gas eater. Back when I had my '74 F250 with a 460, I babied it and still could only nudge 9 mpg in city traffic and not a whole lot better on the road, maybe 11 or 12 at 65 mph and a 4.10 rear ratio. But all in all it sure ran sweet and gas was only about $1.15 a gallon in 1987-89 when I had it.

 

I'm really surprised at the defeatist attitude here. A 460 in your little F100 CAN absolutely get mid to high teens if done right.


I can't tell you if EFI is worth it for you, nor am I up on the current systems. Back when I was I would have suggested the Accel system but now can't say for sure. There's always the stock systems. It really comes down to tuning, many can tune for power, few can tune for mileage, even those who design these systems. There's a lot of MPG to be gained in having a very wide range of perimeters to tune with. Varying O2 voltage goals, wide timing range that can go to 60 deg advance, etc. That said it can also be done with a good vacuum secondary carb like the ones Quick Fuel offers, a good distributor, preferably an MSD, and a wide band O2 sensor/gauge. But that's maybe $700 in carb, dizzy, and all that goes with, so how much more is FI worth. But if you don't intend to put more then 10Kmi a year on it I don't see EFI being worth the money.


They are right about gearing, to get big cubes to get MPG you need to spin them slow going down the highway. A lot of course depends on the engine, cam, compression, etc.

 

Just don't use the original Motorcraft carb as many were recalled when a plug would blow out of the front of the carb and blow fuel into the fan. The results were catastrophic.

 

I know I hacked your quote and I do think the return on investment for and EFI upgrade would be long. That said, I am surprised nobody has tuned a 460 EFI for mileage. I've seen what I can do with 347 built for drag. Huge cam, heads, intake, injectors. It's ODB1 so tuning isn't simple, but with control of all the parameters my engine can be tuned to get 8mpg, or about 20 at cruise.

A carbed 460 is different. If you start with a good running 460, you aren't going to tweak the carb and timing a bit and suddenly see a 50% increase in fuel mileage. "Done right" as you put it, means the entire combo needs to be well matched during the build. MPG shouldn't be an afterthought or you are highly likely to get about 10 mpg like most everyone else. Overdrive with a cam and induction carefully selected to work together in the same rpm range.

I agree mid teens is achievable carbed. These trucks are not that heavy compared to a typical factory 460 application.

 

It's an unfortunate truth that some engine designs are just inherently inefficient. The 385-family is famous for lousy efficiency.

 

The question is does anybody know exactly why and what experience do we have in fixing it. We can all guess but does anyone have actual experience?

Ross, I assume that the 385-family includes the 390?

 

390 is in the FE family, predecessor to the 385. Also not known for efficiency. (By efficiency I mean BSFC -- brake specific fuel consumption, gallons per hour per HP).

I'd suspect both the FE's and the 385's suffer from poor swirl in the incoming fuel mix, poor turbulence in the combustion chamber, and other "intangible" issues. When emissions performance became required, Ford redesigned the combustion chambers several times, maybe to address those kinds of things.

 

I'll get in trouble for saying this here but most Ford factory cylinder heads are mediocre at best. Awful is probably more accurate for a lot of the 70's-80s heads. They don't make power and they aren't efficient. They work OK in some small rpm range that works for the vehicle. (5.0 Mustang is a great example of that). Of course there are exceptions, but they are very few. You can install an aftermarket head with basically no other mods and see a dramatic % increase in power. Fuel efficiency will be as good or likely better if you have any tuning ability.

 

Agreed, though IDK why you would tune for 8MPG. Back when I was getting paid for it I tuned a EFI 540ci in a suburban and got 18MPG, totally doable. With a carb it's different, not impossible, it all depends. Some aftermarket EFI systems suck for MPG they don't have enough variation available. Variations that can be done with a good carb and distributor. Ideal EFI vs. ideal carb, EFI will always do better though.


We don't have enough info about the rest of the engine to say much more.


The 385, much like the 335 is a basically sound engine design capable of both power and MPG with decent heads that was RUINED by emissions shortcuts. Neither will ever be awesome MPG engines, the heads weren't designed for intake swirl, and big bore increases detonation. But get a good quench and a good tune and it will do as good as any other big block.

 

I wouldn't purposefully tune for 8mpg of course. Just a by product of a race tune vs street tune. It supports your point though. If you have the ability to tune a factory style EFI it's amazing what can be achieved. In my example I am speaking of an EECV EFI ODB1 setup with a piggy back tuner card on the the stock PCM J3 port. No reason it wouldn't work well on a 460. Wish my truck was EFI as I would love to see what I could do with it. Maybe someday.