Head milling.

[Don Dulmage <big-d@xxxxxxxxxxxx>]

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To get most castings (906, 452, 346 etc) just to factoy specs (ca 80ccs) it is often necessary to remove between .060" and  .090" . In this case the intake manifold face of the head must also be machined. For every .010" removed from the head gasket surface  .0123" (most shops just use .012") must also be removed. Ideally the block center rail between the two head gasket surfaces should also be machined but unless one is blue printing the entire engine it is rarely done and will work just fine without it. 
Things to do are the intake manifold at the very corners that sit on the top of the block and turkey pan intake gasket must be relieved to they don't hold the intake up of the sealing surface . Sometines happens in stock applicationa also. This is a 2 minute job with a die grinder . I cut the sharpe edge off all four cornerrs underneath about 3/4 to 1" back. All that is necesary is to make sure that sharpe corner is not holding the manifold up of the head surface. Try it and you will immediately see what i am talking about. 
I seal the corners of the intake pan or tray with silicon and often use a old chisel with the nose rounded off to make sure the tray conforms to the shape a bit closer there. 
Pushrods are often no problem but if they are a bit long we have no hesitaion about shimming the rocker shafts. We use 3/8" flat washers that conform nicely to the shape as you tighten them. You don't want the plunger bottoming out in the lifter , nor do you want it hitting the snap ring. This is easily checked before the intake manifold and tray go on. Of course with adjustable rockers this is irrelevant. Often  shimming is not necessary as the lifters have a lot of plunger travel anyway and after all we are just putting the clyinder heads just in factory design spec , not going below it. 
There is a LOT of power to be had here so it is well worth doing. A competet machinist should have no trouble understanding this or doing it.
How much can you remove without cutting the intake side of the head? General speaking a .030" cut will not require any further mods. 
Now someone is already thinking, (I can feel it already) .060" to.090" off the heads is too much. NO it is not . We are putting the heads in factory specs as per the engines original design. We are NOT venturing into experimantal territory. 
Chrysler makes especially thier BB block heads generoulsy thick. Unfortunately that also makes them big on combustion chamber volume and low on compression. Add to that that most of us use Felpro Blue head gaskets (The worlds best) and they are .020+ " thicker than the stock head gaskets which were .019" to .021"  depending on source we are giving away gobs of compression.  Compression is good for HP. 
I make every effort even on street engines to bring the compression back in to stock territory  otherwise a 10 to 1 383 or 440 becomes really a 9.2 to 9.5 383 or 440 . Just so you understand the significance of this  band Xs heads are closer to thier factory specs than ours as are also the small block Mopars. This is real important. 
Sorry i wrote so much, must come from my years teaching engines at Provicial trade school. 
My apologies. 
Anyway that is the scoop.
Don 

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