Thread: ford fe 360 to 390 conversion

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I have a 1969 f-250 with a 360. I am looking to convert to a 390 crank, use original rods and punch it out a little. I have a set of pistons that have the valve indentations in it. Is is doable with 360 rods?
Thank you in advance.

Originally Posted by slugoz

I have a 1969 f-250 with a 360. I am looking to convert to a 390 crank, use original rods and punch it out a little. I have a set of pistons that have the valve indentations in it. Is is doable with 360 rods?
Thank you in advance.

Post the part number of the pistons and also the casting number of the heads (just above the exhaust ports, about halfway back from the front of the motor). I'm planning to figure your static compression ratio. With iron heads, it may be too high to support use on pump gas without detonation.
My batting average for having an ongoing conversation with a one-time poster isn't real good, so if I never hear from you again, good luck with the poke and stroke.

HE! HE! Tech,Your killing me.

Ha! Ill stick around. The casting # is C8AE-H. I inherited the engine as a short block with the pistons, crank and pan already installed. The piston part number I dont know without taking apart. I do have a picture of the tops and I know that it has been punched out .030. They appear to be flat tops with valve indents. The heads are 360, I was entertaining the idea of putting 390 heads on it, but I dont have to, dont even know if they are any different. I dont want a hot rod just a working truck.
thanks again

The block deck height is 10.170". That's the measurement from the centerline of the main bearing bore to the block deck where the heads bolt on.
Bored 0.030", the cylinders will measure 4.082".
390 crank stroke is 3.784", so crank radius is 1.892".
Piston deck height (piston crown to block deck with the piston at TDC) is 0.010" and displaces 2.1 cc's
390 rod length is 6.490".
Combustion chambers are 74 cc's.
390 piston compression height is 1.778".
Crank radius of 1.892", plus rod length of 6.490", plus piston compression height of 1.778" added together makes a parts stack of 10.160. When fitted to a block that has a block deck height of 10.170", the result is a piston deck height of 0.010".

Now, let's shoot the static compression ratio with the above parts.....
(.7854) x 4.082 x 4.082 x 3.784 x 16.387 = 811.5 cc's in the cylinder.
(.7854) x 4.082 x 4.082 x 0.010" x 16.387 = 2.1 cc's in the piston deck height.
74 cc's in the chambers.
Estimate 8 cc's in the piston crown eyebrows.
Estimate 9 cc's for the head gaskets.
811.5 + 2.1 + 74 + 8 + 9 = 904.6 cc's total.
Deduct the cylinder cc's from the total 904.6 less 811.5 = 93.1 cc's.
Divide 904.6 total cc's by 93.1 cc's and find 9.71:1 static compression ratio.
Should squeak by on premium pump gas.
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You said the 390 rod length is 6.490". Will the 360 rods in the engine now work? Are the 360 rods Longer? I can definitely live with buying hi-test fuel its has 3 tanks anyway I already know I am going to get a hand written thank you letter from the middle east every time I fill up.

I believe 360 rods are a little longer, at 6.540", and would pop the piston out of the hole by about 0.040".

bummer, if I understand you right I guess I need to drop the pan and replace the rods. I guess I have a project this weekend. Thanks again for doing all the math.

There is another way, you could use a really thick head gasket, like 0.080" and make the long rods work. 0.080" would allow the pistons to come up 0.040" out of the hole and still have a 0.040" squish.
http://www.summitracing.com/parts/sc...view/make/ford

Personally, I wouldn't do this. I'd use the proper parts in the first place.
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I dont't want to do anything half-a**ed, and I am a bit of newbie at this stuff, I think ill take the advice and get some 390 rods. Glad I thought to ask.

yes, you do need to drop the pan--------------are you messing with us??????????

Originally Posted by jerry clayton

yes, you do need to drop the pan--------------are you messing with us??????????

HEY i know this guy that has a neat pin machine could off set the pin bushing buy 020 to 030 . ALL hell I better not say any more .... am I messing with every one ?? or not

Originally Posted by slugoz

I dont't want to do anything half-a**ed, and I am a bit of newbie at this stuff, I think ill take the advice and get some 390 rods. Glad I thought to ask.

Before you spend a lot of time looking for used 390 rods, then spend money having them checked for cracks, new rod bolts, and resized, you might want to consider a set of aftermarket rods for the engine..... the cheap one's are imports, but a lot of guys use them and say they're fine in a mild street engine????? Just a another thing to consider....

If thats a green pin machine------------

hell 020-030---can't you just use a drill and a bottle brush hone to open them up for that much clearance and let them squeese the piston down when it hits the head?????????

One of my favorite things to do with that was bush the ends of Ford 460 rods down to bbc 990 size for full floaters in custom 4.375 pistons(more jet boats and trucks than race cars) I could get rings at that size at THAT time in history------and the piston people hat forgings for the BBC at that size--------

but really, have you ever see on this(or other) forum anyone talking about correcting the length of the rods?

Originally Posted by jerry clayton

If thats a green pin machine------------

hell 020-030---can't you just use a drill and a bottle brush hone to open them up for that much clearance and let them squeese the piston down when it hits the head?????????

One of my favorite things to do with that was bush the ends of Ford 460 rods down to bbc 990 size for full floaters in custom 4.375 pistons(more jet boats and trucks than race cars) I could get rings at that size at THAT time in history------and the piston people hat forgings for the BBC at that size--------

but really, have you ever see on this(or other) forum anyone talking about correcting the length of the rods?

DID we go to far jerry ????????