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You got a leaky spark tube...
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Discussion Starter · #1 ·
The main studs for my 400 SBC arrived today and I'm going to be taking the block to the machine shop some time in the next couple of weeks to have the block inspected and, if satisfactory, have the block bored as necessary and .020 removed from the deck surface to bring the deck to 9.005". My question is this, when material is removed from the block will I need to have the intake manifold machined to compensate for the shorter deck height? If so, how do I determine how much will need to be removed?
 

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I know I've seen a formula for this, but I think that the difference in deck height (.020) would have to be removed from both sides of the manifold (.020 on each gasket surface). Don't forget to factor in head resurfacing also, not just block decking.
 

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don't mill the intake till you have done a dry fit measurement after decking...

mount and torque the intake with gaskets and no end seals.....

measure the ends gaps with a feeler guage, if you still have about a .030" gap your "OK"....but

small chance you will need to enlarge the heads ports top and/or bottem

the only "real world" way I know to check for port top and bottem alignment is to use a open plenum intake and a coat hanger to "feel" for an edge

never have done a 400 but for alot of motors....decking .020" is the practical max before alignments become a major issue....deck it less and sleep better

most blocks will clean up to true flat at .007 to .010 decking....
the extra compression gained by decking .020" will gain you next to no more HP (one full comp point=4% power gain)

if you do deck it .020" you will probably need different pushrods

the Ford formula for how much to remove from the intake:
.020" off the heads =.010 off each side and .014 off the bottem
(for a stock intake and heads)
 

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You got a leaky spark tube...
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2,854 Posts
Discussion Starter · #6 ·
Thank you for the responses. The reason for decking the block is to bring the quench to .045". The particular head gaskets I've found are .040" and the particular piston I plan to use will have a height of 9.000".
 
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