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Looking for some input on this 390. Heads are D2TE and had a factory 4V intake. I bought it without seeing it run but was told it was rebuilt. I pulled the heads for inspection and preparation for possible rebuilding. I measured the bore at 4.075 but used an old crappy set of dial calipers so I’m thinking 20 or 30 over bore currently. I think judging by the heads it has some valve seal or ring issues. The pistons have four valve reliefs and a smallish dish. I can’t see a brand or over bore indicator on them. I can see cross hatching in the bore as well. I didn’t do a compression check before I pulled the heads. Probably should have.
I’m trying to decide on how deep to go on the rebuild. I will be doing a new cam and lifters and valve job on the heads. Should I pull the pistons and hone the bores? Tune the same crank and rod bearings or pull the works while I’m there?
And would those pistons work with larger CJ valves? With the dish I’m guessing it’s pretty low compression wise.
390's from '72-on were pretty low compression - my Motor's manual says 8.2:1 for 1972 through 1976.
The heads will take the larger CJ exhaust valves, and you might as well, because unless the heads had hardened exhaust seats installed, the factory induction-hardened exhaust seats are no longer all that hardened
Pickup 390s used the Mercury 410 piston, with a compression height of approx 1.66". Passenger car 390s used a flat or dish, both with an approximate CH of 1.77"
At TDC, how far down the hole are your pistons? .015 or so or .100+?
I think the 410 piston was a flat top with the valve reliefs. The slight dish might be a car "Regular Fuel" 2bbl piston, advertised as 9.5 CR as OEM. ('66 and up). So if your pistons are almost at the deck, you're "good".
390's from '72-on were pretty low compression - my Motor's manual says 8.2:1 for 1972 through 1976.
The heads will take the larger CJ exhaust valves, and you might as well, because unless the heads had hardened exhaust seats installed, the factory induction-hardened exhaust seats are no longer all that hardened
That'll be useless unless the port work and bowl blending is done to match the larger valves. At that point he may as well buy new Edelbrock heads as the cost to rework the iron heads will be at that level. Those pistons look like the 2 bbl car (Ford not Merc) pistons.
That'll be useless unless the port work and bowl blending is done to match the larger valves. At that point he may as well buy new Edelbrock heads as the cost to rework the iron heads will be at that level. Those pistons look like the 2 bbl car (Ford not Merc) pistons.
Very true... I "assumed" that would be done as well - and yeah, I dropped the ball, it's always a question at the point of "do I just buy these shiny new ones?"
Very true... I "assumed" that would be done as well - and yeah, I dropped the ball, it's always a question at the point of "do I just buy these shiny new ones?"
You got it ! I did a set of Low Riser 427 heads almost 40 years ago with all new seats and guides and those set me back $800 then.
You got it ! I did a set of Low Riser 427 heads almost 40 years ago with all new seats and guides and those set me back $800 then.
Same, on a set of C8AE-H heads, new seats, guides, cut for bigger springs, you name it. If my machinist didn't take it as a teaching moment and make me do all the work, I can't imagine how much time that would have cost.
Just to satisfy my own curiosity here’s the tag from the intake. Anyone want to take a stab at decoding that? I’m pretty sure it’s just garden-variety 72 390 4V. This is going to be a pretty mild build for a 65 four-wheel-drive. I’m considering upping the compression a bit if I need to bore it over any more than it is.
Just to satisfy my own curiosity here’s the tag from the intake. Anyone want to take a stab at decoding that? I’m pretty sure it’s just garden-variety 72 390 4V. This is going to be a pretty mild build for a 65 four-wheel-drive. I’m considering upping the compression a bit if I need to bore it over any more than it is.
Decode what ? There's nothing legible on that tag in the picture
That's better. If the tag is still there, it's a good chance it's never been into. What do the gaskets look like ? Any non factory bolts present ? Next to look for is a reman tag on the block. Oversized pistons will have the oversize stamped into the piston tops, you'll need to wire brush the carbon off to see it usually
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I did a set of Low Riser 427 heads almost 40 years ago with all new seats and guides and those set me back $800 then.
