deck the block, or deck the head?
Thread Starter
12 Second Club
Joined: Feb 2006
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From: Catlettsburg, Ky
deck the block, or deck the head? let's here your opinions on this as far as a performance benefit.
I figure everyone decks their heads for more compression, and it works. but still leaves the piston .02x" in the block.
why not deck the block the same amount, or maybe just 75% of what you would deck the heads to? the "quench" area will be greatly reduced when decking the block. as well as the overall combustion chamber volume in CC's.
think about it, .015" off the combustion chamber in the head is??? what? 3cc's, maybe? the combustion chamber is not 4.00" circle, so when taking the same .015" off the deck of the block, how much area you reducing the combustion chamber by?
I know people generally "zero deck" a block for this reason, and it seems like a great idea to me, as well as leaving somewhat of a safety margin for the future.
if you deck the heads to the max (or safe max atleast...) then drop a valve, or have some other form of catastrophic engine failure, and need to re-deck the head to clean them up, you're screwed.
deck the block and you still have the full deck thickness of the heads to work with, not to mention a thicker deck on the head means less chance of warping under pressure (i.e. notice how AFR boasts having a 3/4" thick deck, as opposed to the stock being like... 9/16 to 5/8" thick)
this may be old news, or already been talked about and drug under the bus a hundred times already.. but it just seems like it could be a small step in making an older design motor a little more efficient.
I figure everyone decks their heads for more compression, and it works. but still leaves the piston .02x" in the block.
why not deck the block the same amount, or maybe just 75% of what you would deck the heads to? the "quench" area will be greatly reduced when decking the block. as well as the overall combustion chamber volume in CC's.
think about it, .015" off the combustion chamber in the head is??? what? 3cc's, maybe? the combustion chamber is not 4.00" circle, so when taking the same .015" off the deck of the block, how much area you reducing the combustion chamber by?
I know people generally "zero deck" a block for this reason, and it seems like a great idea to me, as well as leaving somewhat of a safety margin for the future.
if you deck the heads to the max (or safe max atleast...) then drop a valve, or have some other form of catastrophic engine failure, and need to re-deck the head to clean them up, you're screwed.
deck the block and you still have the full deck thickness of the heads to work with, not to mention a thicker deck on the head means less chance of warping under pressure (i.e. notice how AFR boasts having a 3/4" thick deck, as opposed to the stock being like... 9/16 to 5/8" thick)
this may be old news, or already been talked about and drug under the bus a hundred times already.. but it just seems like it could be a small step in making an older design motor a little more efficient.
TECH Junkie
Joined: Dec 2005
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I used a .028" head gasket and had the block decked so that the pistons were .007" in the hole. That gave me a quench of .035".
I had the heads milled to give me the compression ratio I wanted. I had .035" taken off the heads to give me a 10.75:1 compression ratio. This is on a L98 motor but the principle is the same.
I had the heads milled to give me the compression ratio I wanted. I had .035" taken off the heads to give me a 10.75:1 compression ratio. This is on a L98 motor but the principle is the same.
When you get head work done at most places they mill the heads. you can deck the block down to 0 also. but when doing this you have to make sure everything matches. My 355 build i have my block 0 decked and my heads are being milled to 55-56 cc chambers also my intake will be milled for correct port alignment. along with this my head gasket will be 0.29 quench with -5cc flattop pistons my compression will be around 11.7.1. either way you do it it will help I think there are some people on here with the heads down to 52cc chambers
A lot of us do heads and cam long before a full engine build and I think that is often where the heads get milled in search of compression.
If anyone is milling the snot out of the heads and leaving the pistons .020 down on a full build they need to rethink their stratagy.
If anyone is milling the snot out of the heads and leaving the pistons .020 down on a full build they need to rethink their stratagy.
Thread Starter
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Joined: Feb 2006
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From: Catlettsburg, Ky
Originally Posted by 96capricemgr
A lot of us do heads and cam long before a full engine build and I think that is often where the heads get milled in search of compression.
If anyone is milling the snot out of the heads and leaving the pistons .020 down on a full build they need to rethink their stratagy.
If anyone is milling the snot out of the heads and leaving the pistons .020 down on a full build they need to rethink their stratagy.
obviously shaving the heads just the bare minimum to assure a truely flat surface is what you would want, right? wouldn't decking the heads excessively have an negative effect on valve shrouding?
my plans for a motor would include zero decking the block, and decking the heads just enough to clean them up. I think .020" off the block would shoot the compression up MUCH higher than .020" off the heads. any idea as to what the compression would be with stock heads and a zero deck???
typical performance gains?
