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whd507 08-16-2004 12:12 AM

391 truck engine
can anybody confirm that a 1974 391 has only 7.4 to 1 compression?
will 390 pistons raise compression? or should I just get FE heads/intake?

the 391 runs like a swiss clock, but while adequate power is there, I want more... :-X22

also, anybody know the compression ratio and HP of a 1979 370 2v? 4v?

does it use the same timing chain setup as a 429/460? I was thinking of advancing the cam timing that way.

I just replaced the OEM duraspark, as it was speed limited, with a petronics setup, that alone feels like 20 hp. (plus its way faster) :rolleyes:

it runs pretty good, but I will have to find a 68-71 4v intake and install an edelbrock carb. (I'm afraid to mount the HD thermostat housing on an aluminum intake)

also,my second 1979 F-600 has an eaton 2-sp axle in it, code F2M, and a trans code of 2A. I'm pretty sure that the trans is an OD unit (clark)but I'm not sure.

anybody have a shop manual that would tell me the axle gear ratio?

lrd56 08-18-2004 02:57 PM

391 information
i have a 70 391 .it has heads will fit .i was told that in order to use a 390 have to change the oil pump .pump you can use a 390 dist.thats only if you want to get away from the governed carb and dist.i personaly like the governed stuff less chance of blowing it 391 has a big flywheel that has a 13 inch clutch .id like to be able to figure out how to use the big flywheel and clutch on my 78 300/6 .or at least the 13 inch clutch.
hope this helps
lrd56 a happy dinosaur

rusty70f100 08-31-2004 09:05 PM

Ford 360 pistons will raise compression a good amount, more than 390 truck pistons.

OBTW, the 391 is an FT engine, closely related to the FE. Ask in the FE forum. :)

whd507 09-01-2004 05:22 PM

I know, but there is so little information about FT engines in the FE forum, I figured I'd get more help here.

360 pistons have a differnt pin height, wouldnt they hit the head?

Loan Ranger 09-24-2004 04:23 PM

The BEST single source of information about all of the FE and FT engines is the HP Book (part number 708) "How to Rebuild Your Big-Block Ford" by Steve Christ. It gives, of course, rebuild procedures for all of the engines but it also includes casting numbers, part numbers, interchangablility, parts dimensions, compression ratios, HP ratings, torque ratings, and some high performance parts sources for each of the engines. I do believe it is available from

rusty70f100 09-24-2004 04:43 PM


Originally Posted by whd507
I know, but there is so little information about FT engines in the FE forum, I figured I'd get more help here.

360 pistons have a differnt pin height, wouldnt they hit the head?

No. Your pistons now have a humongus dish in 'em. They have a 1.757" compression height. 360 pistons only have valve reliefs, no dish, and have 1.776" compression height. This will give you .016" deck clearance. This is as perfect as you can get in this motor. This should yield 9:1 compression. I'd also change the cam out to a Crane 343901. This should wake up that 391 a good bit. Keep in mind that the heads have small ports and valves, and dont flow very well. So it wont perform as well as with 390 heads. But for low end torque these mods will help a lot.

whd507 09-25-2004 01:30 AM

Thank you! I hesitate to mess with the 391 as it runs so well, but we might be re-locating cross-country, and driving a gutless wonder that far would make me consider a piston swap, and cam.

what about the cam gear? is there an advanced timing version?

390 heads, 360 pistons (why not 390 pistons?) edelbrock intake, headers etc.


rusty70f100 09-25-2004 12:56 PM

You could put regular 360 or 390 heads on it. They will flow MUCH better than the heads you have now. Problem is, you have to replace the intake too, since the FT intake wont match up to the FE heads. Also, you'll need to use an FE distributor and get a bushing for the block, since the FE distributor is smaller than the FT one. You can get one at DSC and they call it the "Ford Truck Block Distributor Bushing." It's about 3/4 of the way down the page.

You dont want 390 pistons. Most of them are the truck variety and have a 1.680" compression height. This will lower compression back down, and make a gutless wonder. FWIW, some 390 car pistons have the correct 1.776" compression height, and are the same part as 360 pistons. Just tell 'em you want 360 pistons and you cant go wrong.

Cam gear might be a problem. The FT has a bigger crank snout than the FE, so that prevents you from using the aftermarket pieces available. What I would do, is get a replacement FT timing set and use the aftermarket cam with it. Should work good.

If you decide to do a head swap and use FE heads, your compression will go up since you will have less combustion chamber space. In this case, use the Crane 343941 cam. Then you'll have a real runner. The difference will be night and day.

twotrout 11-27-2010 05:10 PM

what size are the freeze plugs on the sids of the block

85e150six4mtod 11-27-2010 10:02 PM


Originally Posted by twotrout (Post 9608753)
what size are the freeze plugs on the sids of the block

Welcome the FTE. Asking questions on a 6 year old thread will get you nowhere.

On the sides of the block of what? A 391? 1 1/2" if so.

Best to make a new thread in the FE/FT forum, or google it. I found they are all the same for FE/FT, according to several search results from Dorman and others:

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