How much can a 383 block be decked or cleaned up before milling of the valley wall tops is necessary? Do it always no matter what or only do it after a certain amount? Thanks in advance!

Don't cut the top of the block between the heads unless you want to spend a bunch of time and money on getting a correct fitting valley tray made to fit
Mopars old hot rod and race engine bibles says to cut .012 off the intake surfaces of the heads for each .010 cut off the head deck surfaces or on the block, I think

Yes I would definately cut the intake side of the head as well. I just thought the tops of the block where the valley pan bolts down needed to be addressed but if they don't then thats good.

That is the way I was taught at the machine shop I worked at years ago. Cut .012 on the intake side of the heads for every .010 cut off the deck surface and leave the ends alone.

To go a bit further if desired you can check head port to intake port alignment on the "slope" & adj the .010/.012 formula as needed to get a dead on match. check lifter preload. EDIT check intake flatness

To answer your question. It depends. Only a slight clean up on the deck, probably don't bother. But if your cutting the deck, head and intake side of head, then yes.

If you are going to deck the block a bunch, you would cut .017" off the walls for every .010" you deck the block. This will maintain the optimum pan gasket fit.

hi

yes you must cut the valley rails !

17 for every 10 from deck !

if you dont do this the gasket will sit too high and ports will not line up !

Wouldn't your final fitment depend on head gasket thickness?

OEM motors used a steel shim gasket (apx. .025 thick). While standard felpro's are .039 if I remember right. Milling .010 off block or head wouldn't really change anything, until you go beyond ..010 to .015 total cleanup.

It is one of those things that you just have to check. These blocks are 50 years old so who knows what kind of shape they are in. Get the block squared up and then drop your cylinder heads on there and see how things line up. The head, the valley rail and the deck should come together at a point if everything is correct.