I’ve never had it done. A coworker asked me about it as we were taking. I’d mentioned milling heads down at some point causes intake seating issues that require some more machine work. He asked about a block. I said “I don’t know, but would ask those who do know”. So if a block is decked zero, or trued, when would one be concerned about the intake angle?
If you deck a block to get the deck height zero, and the pistons you are trying to match are pretty low in the hole, then you might have to worry about it. If you're just squaring the block and not taking off more than, say, 0.020", then it should not be an issue.
One other worry when decking a block (depending on the block itself) is the possibility of removing identifying numbers/stampings that could dramatically affect its value. This is true when dealing with many SB and BB Chev engines. Got an L88 Vette with the original block? Deck the original block and you (most likely) lose proof that it is actually the original block to that car. Sure, things can and do get restamped but ... Just something to keep in mind.
Just had a block decked last week but only took .005" off to clean it up. Glad this thread came up since we also took .020" off the heads to true them up. I will need to likely pay attention to the gap between the intake and heads to make sure they seal up.
A true "decking" of a block is much more than just making a "skim"cut on the deck surface, especially in a race motor! Prior to any machine work being done, the block is measured to determine the distance from the crankshaft centerline to the deck surface, usually (at least on a v8) on the 4 corners of the block to make sure the block is aligned with the crank & that the distance actually is what is considered "spec" for that motor(I seem to remember 9.25" for small block Chevrolet), although there may be a good reason your machinist may want to hold a slightly different number! You'd be surprised how much a production engine may vary in those dimensions, not only front to back, but from side to side, but to make a race motor the foundation(the block) needs to be "trued-up" as a starting point! Once the amount(s) needing to be removed are determined to block will be aligned to the centerline & the deck surface is squared in both dimensions to the crank, then a machine p*** will be made to bring that bank to the desired number, then the process will be repeated for the other bank so now both banks are at 90degrees to each other & the same distance from the crank. Now the block is finally ready for the rest of the machine work needed to turn it into a true race motor!
Decking the block doesn't alter intake angle , only intake height. I would prefer to deck the block than mill the heads because less height is removed to achieve the same results [in compression gains] I prefer to run most of my engines with the pistons approx 0.005" above the deck [this practice is now used by GM on LS engines] When you mill the heads, the intake also needs to be milled.....AND the same also applies with the deck. On a 4" bore a 0.020" deck cut reduces the total TDC volume by 10.16cc To achieve the same reduction in volume on a 76cc smogger head would require milling the heads 0.070" [A good ballpark figure for the SBC head is .007" per cc] With a 20 thou decking you could probably leave the intake as-is [or maybe drill out the bolt holes slightly] And leave the valley end gaskets off by using silicone. A 70 thou milled head would require the maiinfolds to be milled on all 3 surfaces and the head is more susceptible to cracking. There is a downside to decking a block , it needs to be "dummy ***embled" if bored, then measured and dismantled again Most SBC's are 20 thou down the hole, but rebuilder pistons can go down a further 25 thou. On our 57 we cut 50 thou to get the pistons 5 thou above [this would've been impossible to do with the heads alone]
On sbc/bbc diffrent thickness intake gaskets can correct milling , some time intake will need to be cut
Any performance engine I build gets piston to deck height measured and cut accordingly . And yes would be amazed at how many are really out of square. As far as decking and removing numbers off a valuable performance block , my machinest will stop short of decking the numbers off . He just did a 69 Z28 DZ block for me and left the numbers on.
When I was racing, I had my 400 small blocks cut just enough to make them flat. They had a tendency to have head gasket leaks between the middle cylinders.
Old rules, if you cut heads .030 the intake needed like .015 per side removed, not an equal amt. Small cuts just got thicker gaskets. Unless someone is going all out like described above the solutions are easy. Numbers, if you have to deck a seriously collectable block shame on you for lack of do***entation or efforts to save those ID #s. If your machine shop won't lift the cutter to save em you need another shop. Cheers...
If you cut the intake side of the head you can leave the intake manifold alone .025 should not be an issue steel shim to composite head gaskets has almost that much difference. Calculator for intake side. http://wallaceracing.com/calc-intake-mill.php
May be hard to tell from the pic, but looks good to me with no gaskets. I never use the end gaskets anyway, so should be fine.
Irrespective of saving block numbers, this is why Billy Bob's Boring and Decking charges so much less!
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