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Old 12-26-2012, 10:04 AM
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bbc dome pistons block decking

Hello
my question is what value would decking the block have in a bbc with dome pistons , not crazy 13 to 1 pistons but 10.5/11.5 to 1 type..
take my 489 pistons..


most of the piston is somewhat flat top.. with a small dome..
with an engine with true decks,,
what am I giving up not zero decking the block.. in power over strenth of the deck??
as it might see boost or happy gas..

this is my first big block.. and I've had issues with small blocks deck failure when decked and sprayed..

this may run like a raped ape and not ever get any boost.. but I'd hate to deck the block and gain nothing from it..

discuss...

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Old 12-26-2012, 10:39 AM
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Just maintanance decking? or to spec. BBC decks are fairly thick so decking to reasonable spec won't compromise strength.

I always shoot for .040 total quench on performance builds. Usually leaves piston close to even with deck. on assembly. I have never had head gasket problems on properly done BBC's.

Last edited by BOBCRMAN@aol.com; 12-26-2012 at 10:44 AM.
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Old 12-26-2012, 02:00 PM
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bbc dome pistons block decking

What brand pistons are you using? I have the IC789 pistons in my engine. Here why I think it is important to deck the block. I bought the forged rotating assembly from CNC Motorsports with them internally balancing it. I assembled the crank using plastic gauge checking the bearing clearances. Well after I after installed all the pistons I decided to check the deck clearance. Boy what a shock. On the #1 cylinder I had .017, #3 & #5 I had .016, and on #7 I had .019. The other side of the block was about the same. Well I thought about it for a couple of days and decided to call my machinist. I didn't like what he told me but it made sense. Well since I had to take it back apart I decided to replace 2,3,and 4 main bearing caps with Pro-gram 4 bolt main caps and have it align bored and decked and new Arp bolts. Ended up with .005. I used Cometic MLS .036 compressed thickness head gaskets to have .041 quench. You don't really need zero decking, but you want all cylinders the same. To me zero decking is just a way to save money by using the gaskets in a gasket kit usually .039 or .041. So if you haven't milled the deck on your block what are your clearances.
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Old 12-26-2012, 07:51 PM
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Quote:
Originally Posted by cdminter59 View Post
What brand pistons are you using? I have the IC789 pistons in my engine. Here why I think it is important to deck the block. I bought the forged rotating assembly from CNC Motorsports with them internally balancing it. I assembled the crank using plastic gauge checking the bearing clearances. Well after I after installed all the pistons I decided to check the deck clearance. Boy what a shock. On the #1 cylinder I had .017, #3 & #5 I had .016, and on #7 I had .019. The other side of the block was about the same. Well I thought about it for a couple of days and decided to call my machinist. I didn't like what he told me but it made sense. Well since I had to take it back apart I decided to replace 2,3,and 4 main bearing caps with Pro-gram 4 bolt main caps and have it align bored and decked and new Arp bolts. Ended up with .005. I used Cometic MLS .036 compressed thickness head gaskets to have .041 quench. You don't really need zero decking, but you want all cylinders the same. To me zero decking is just a way to save money by using the gaskets in a gasket kit usually .039 or .041. So if you haven't milled the deck on your block what are your clearances.
what are my clearances, no idea, the block has to be bored 30 over first.. straight edge shows flat decks, have to get it bored before I can do a mock up.
pistons are srp floaters on a 6.35(iirc) rod 4.25stroke..
have to look bought all the parts in '02..
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Old 12-26-2012, 08:02 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
I always shoot for .040 total quench on performance builds. Usually leaves piston close to even with deck. on assembly. I have never had head gasket problems on properly done BBC's.
I agree.

You set your quench with your block deck, and then you juggle your dome and chamber volume for the static compression you need to achieve for the fuel you will be using.

Proper quench will actually help PREVENT detonation.
( especially important with pump-gas street engines )
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Old 12-26-2012, 08:10 PM
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Quote:
Originally Posted by gearheadslife View Post
what are my clearances, no idea, the block has to be bored 30 over first.. straight edge shows flat decks, have to get it bored before I can do a mock up.
pistons are srp floaters on a 6.35(iirc) rod 4.25stroke..
have to look bought all the parts in '02..
( SAME setup I am running. )

Bore the block, mock it up, and then you can check your "piston head"-to-"block deck" clearance.
My pistons were too deep in the block, I had to deck my block to get the correct quench.
Decking the block is a good idea. You get a virgin surface, and you get the exact clearance you need.
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Old 12-26-2012, 08:27 PM
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seems to me after reading on the newer gaskets, different ones like different deck surface finish..

haven't looked into head gaskets any farthar than that..
this builds been a long time coming..
I mean who buys all the hard parts and shelves it for 11 years..lol
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Old 12-26-2012, 09:12 PM
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bbc dome pistons block decking

Quote:
Originally Posted by gearheadslife View Post
what are my clearances, no idea, the block has to be bored 30 over first.. straight edge shows flat decks, have to get it bored before I can do a mock up.
pistons are srp floaters on a 6.35(iirc) rod 4.25stroke..
have to look bought all the parts in '02..
That is why most people just zero deck the block at the same time the block is in the shop to be bored. It is a pain to bring it home and mock it up to find out your pistons are .020 down in the hole at TDC. Then you need a .020 thick head gaskets to get a quench of .040 which is not manufactured. Then you have to haul the block, crank, pistons back to the machine shop because they will want mock it up to check all 4 corners and get the measurements before they mill it.
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