I'm thinking about replacing my 460 ci with an "old" ford 390 ci (1965 Ford Farlane) to improve my mpg (I only get 7 mpg, but it runs great!). The info I have on the 390 is that it has about 330 hp (10:1 compression) compared to my 460 ci at 245 hp. The other reason for using a 390 ci is that it will bolt-up to my C6 transmission, and a 351 ci will not. I plan to keep the engine stock of course - this is an RV it's going in. Any thoughts on my idea? TMM

 

Isn't 10:1 a bit high compression for a heavy vehicle like that? That's my first concern. Second, I think going from 460 to 390 will not give you any appreciable mileage changes. I'm a firm believer that an engine must be optimized for the load it will see. Either having too much load or too little will hinder mileage. I have found this article to explain what I mean rather nicely http://www.corvair.org/chapters/chapter017/resources/tips/vv/engine_efficiency.html
Of course, there are those that will disagree with me on some points. So, you will have to review those arguements as well and make up your mind accordingly. However, I would put the time and money you are considering for this swap into the 460 as a rebuild or tune-up. That's my opinion. Let me know if I can help further.

 

I used to be the owner of a 74 4x4. That was powered by a 460 rv cam headers with a c6 auto . I spun a rod bearing due to oil pump problems, and due to work commintments I was short on time and money, so I swapped in a 390 that I had rebuilt for another project the cam was comp cam 272 and I was using flat top pistons with 58 tbird heads
so compression was around 10 to 1. Behind this I swapped in a four speed. the gearing was 4:11 and I was running 33" tires. I saw no increase in gas milage what so ever. I also had to switch to a higher octane fuel. Eric

 

Yeah that will probably require higher octane fuel. Plus I beleive the 390 has a different bell housing bolt pattern.

 

>Yeah that will probably require higher octane fuel. Plus I
>beleive the 390 has a different bell housing bolt pattern.

I think you are right, according to my notes:

351M/400/429/460 take same bell - 7.75" between top bolts
240/260/300/289/302/351W/351C - 5" between top bolts
352/360/390/428cj - 6" between top bolts

 

The 390 will out run and out pull the smog'n'clog 460.
Yet you'll need higher octane gas. Though mileage is
around 15mpg with the engine you describe. You need 390 bellhousing,
motor mounts,perches. The 460 clutch is good to go on the 390.


Dory

 

Dory,

I already run premium fuel in the RV, just to keep it from knocking, so I don't mind the extra expense. Why do you think the 390 will out pull the 460? I don't plan to have any smog stuff on the vehicle, since it's registered out of state. What to I neet to do to the bell housing to bolt it up to my C6? I just rebuilt the tranny and I really don't want to mess with it. Tommy

 

You will need a different trans a 390 wont bolt to a trans with a 460 bolt pattern. On a standard trans you can just change bellhousings. The 351/400m,429,460 share the same bolt pattern.

 

Your 1965 390 HP rating was Gross (flywheel)while your 460 HP rating is Net (rearwheel). Knocking 15-20% off the 330 HP of the 390 engine leaves you around 270 HP which is more comparable to your 460. As one of the other posters says...you'll probably have to run premium fuel for the 390. If your looking for mileage, Bricks (RV's, Pickups, full sized autos) and Big blocks do not mix.
OR
Bricks + BB = Gas Hog squared
Deen

 

sorry, I didn't remember you were equipped with an auto

The post emmissions 460 has lowered compression and retarded cam
timing, greatly affecting performance and power. the 460
has 245 hp, and less than 400ftlbs torque gross. Low
compression would be an good thing for moving heavy stuff, no
knocks, and less heat build up. The old 390 is unsmogged that is
where it gets its power, a 76 390 has pathetic power output from
smog stuff.

 

 

my engine is a true smog era engine and with just the simple mods i have done i have over 300 hp and close to 450lbs of torque. it will pull anything and wi;ll run on spit. still pases emissions and looks great doing it. just waititng till i dont have to smog it so i can put a nice cam in it to up the ante. just askthe guy with the 5.3L chevy that i smoked a few days ago. either way, both engines make good power so just use the one that is easiest, less money to retrofit into your rig.

1977 F250 460
C6 Hedman Headers
Dual 40 series
edelbrock performer
holley 4160
msd 6a and blaster coil