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I have a 390 in my Tbird and the block is from the sixties, about 1965, I think, but the block is cracked. In an attempt to rectify this, I recently bought another 390 from 1974. It was in a truck, apparently. I wanted to take the pair of engines to a machine shop and get the best engine I could from them.

I called the machine shop to explain my plan and they told me that 390 blocks from 70's trucks had different pistons than the ones from 60's cars. And so my idea getting one good engine from two engines was not going to work.

Is this true? Were there different 'types' of 390 big blocks? I was under the impression that all 390 blocks were the same.

Any info appreciated

~K
 

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K
More than likely your 390 from the T-bird is just a stock 390 300hp. The 390 from the truck will probably be a better, more stout block, because it is comming out of a truck. Check the sides of the block for long rectagular ribs, if it does than I would use that block, it might even have the extra webbing at the main caps...(MIGHT) that would be a plus. The bores on the engines should both be 4.050 in. The truck blocks' pistons more than likely have a long skirt on them and maybe a different wrist pin location, if you can get away with honing the the truck block cylinders and use your original pistons and rods, you might just get away cheep.
 

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More than likely your 390 from the T-bird is just a stock 390 300hp. The 390 from the truck will probably be a better, more stout block, because it is comming out of a truck. Check the sides of the block for long rectagular ribs, if it does than I would use that block, it might even have the extra webbing at the main caps...(MIGHT) that would be a plus. The bores on the engines should both be 4.050 in. The truck blocks' pistons more than likely have a long skirt on them and maybe a different wrist pin location, if you can get away with honing the the truck block cylinders and use your original pistons and rods, you might just get away cheep.
Wouldn't this be a 391 then, which also had a larger crank snout negating a different damper???
 

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Not necessarily....it could have been, but Ford used those blocks as service blocks when they ran out of other blocks. you might even find a service block that Ford might have used for a 428. Because there is no specific designation for the blocks, they could have been used in many different applications.
 

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...they told me that 390 blocks from 70's trucks had different pistons than the ones from 60's cars. And so my idea getting one good engine from two engines was not going to work.

Is this true? Were there different 'types' of 390 big blocks? I was under the impression that all 390 blocks were the same.
The key word here is "block"...having different pistons in an engine does not mean the block is different. If that's the terminology your machine shop is using, you might want to look around and compare what others are saying. I'd be a little leary about a machine shop telling me that I can't use a block because the pistons were different. That being said, I do believe they are right about the pistons (someone please correct me if I'm wrong).

The original 390's had a taller piston height (distance between the center of the wrist pin and the top of the piston) and shorter deck height (distance between the top of the piston and the deck) than the "emissions" truck 390's of the 70's. If memory serves me correctly, I think Ford used pistons out of a 410 to bring the compression down. Look at the side of one of the pistons...they might be marked with "410" if they are from that engine configuration, or should be marked with "390 4V" if it follows the original 390 structure.

Here's the fun part though...if you do have the 410 pistons (or if you want to buy them if you don't), you can install a 410/428 crank and 410/428 flywheel/flexplate and have a nice little stroker...that's all that's required for the conversion (410 pistons, 410/428 crank & 410/428 flywheel/flexplate)...everything else can be from a 390. This will change the engine to an externally balanced setup, but the flywheel/flexplate takes care of the difference...just make sure you DON'T use the "hatchet" counterweight from a SCJ.
 

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The truck block does it have on the drivers side front of #5 cyl. 352 or a backwards (mirror image) 105 cast into it.
Years ago I picked up a FT 390 that had 410 pistons in it for low compression in an old work truck.
The 105 block is a great block.
 
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