The FE truck engines generally suffer from low compression, but the heads aren't the problem. The early FE chambers are very good, and the C8 & D2 chambers are excellent. The compression problem occurs because Ford chose to cheap out in the late 60s and early 70s on piston design. The 360 is an overbored 352 with 390 4V flattop pistons- which are about .125 down the hole. Yes, it runs just fine this way, but it burns dirty and sucks fuel and has less power than it should. The 352 should do better for mileage than a 360. But they were cheap to build, and that was what mattered most at the time. In the 390 pickup truck engines, Ford again cheaped out and didn't design a new low compression truck piston, rather, they grabbed off the shelf leftover 410 Mercury pistons. With the piston .125 down the hole again, the engine runs well, but burns dirty, sucks fuel, and has less power than it should. Even more frustrating is the fact that when rebuilding these engines, 999 out of 1000 builds get replacement truck pistons that repeat Ford's cheapout mistake. There are lots of piston choices available, but many guys don't even know to ask about them...........so the old FE gets rebuilt and still has less power than it could, still burns dirty, and still gets only 2/3rds of the mileage that it could be getting. If customers and their machinists spent about 10 minutes thinking about piston choices, they could save thousands of dollars down the road on fuel costs. unfourtunately, most folks don't understand the issue, or don't care.




DinosaurFan, @ his Dad's house

 

Good points Dino...

 

So what gains would you expect by running 10:1 CR that's zero-decked with .040 quench, compared to stock?

 

TX, you could easily get a third better mileage. But the quench has to be right, too wide and the effect is lost. and 10 to 1 would be wonderful, but the engine will not be happy on regular fuel. DinosaurFan, at his Dad's house

 

I gues I just got lucky - '75 3/4 T - SuperCab - LWB - 435 4-spd - 4.10 rear - 4V 600CFM Holly < got 12/1`3 town and almost 18 MPH Hiway - slow/steady foot on the "go pedal" Moved from Denver to E. Tennessee with a LOAD under the Ford canopy and averaged 16 MPG - EXCEPT when I wanted to kick in the secondary - then I could almost watch the gas gauge drop. At times I could "kick it" and feel the secondary kick in. Almost felt like an automatic dropping into passing gear. I'll be building the old 360 this summer with a few 390 parts and Xtras. Want that "kick" back. A steady foot is the key.

 

Yeah and keeping the RPM down below or at peak torque will also help more than anything else.

 

Bear - Two items I forgot to mention, I have a tach AND a manifold (vacuum) gauge mounted on the steering column. I like specific info. AND I watch the mirrors and road ahead - "Smokie" might be taking pictures. Watching the road F/R is a habit / used to ride a bike daily for 30+ years - miss those 2 wheels..!!!

 

Funny you guys mentioned everything but the rear end ratio.
I had a 66 Galaxie 500 that weighted close to 5000 lbs. and with a 3.00 rear end it got well over 16mpg with a 352 4V auto on the freeway. I did drop a much larger mill in the car along with some 4.11's and 50 series tires and mileage went right into the crapper.

Use the gobs of great torque these engines make and gear the rear end higher and grab some mileage back. Of course if your hauling a boat or something heavy...keep the lower ratio and.....bust out the wallet.

 

My 1968 F250 with a custom built towing 390 with a 3.73 rear gear absolutely loved 60 to 62 mph for best mpg. Not towing it would do as much as 13 mpg and towing would do 10 mpg. My 1984 F250, 460 with 4.10 rears, gets 7.5 mpg at 60 mph but at 55 to 58 mph would pull 10 to 10.5 mpg. I suspect the secondaries were starting to open for the drastic drop in mpg, but I have never gotten around to changing the secondary spring to prove this. So yeah, gears make a difference, but only at which speed the vehicle will be at when it gets the best mpg, but not at what RPM the engine is most fuel efficient, that is determined by the engines peak torque RPM.