Decking - how much?
Thread Starter
Racer
Joined: Dec 2008
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From: Toms River NJ
Decking - how much?
the machine shop I'm using wants to deck my block. They say the blocks arent perfectly straight from the factory, so they feel better just running over them. I'm ok with that. My question is how much, on average, do you think he's gonna take off just to flatten it out? Ill call him tomorrow to see what he says, but I'm looking at pistons and rods tonight.
Le Mans Master
Joined: Dec 2006
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From: Oquirrh Mountains
St. Jude Donor '09
Using a composite head gasket, nominal thickness of 0.040", you can usually deck a factory block about 0.020' to arrive at the desired quench of 0.040" clearance. The best way is to get the pistons/rods and mock it up for measurement.
Le Mans Master
Joined: Apr 2006
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the machine shop I'm using wants to deck my block. They say the blocks arent perfectly straight from the factory, so they feel better just running over them. I'm ok with that. My question is how much, on average, do you think he's gonna take off just to flatten it out? Ill call him tomorrow to see what he says, but I'm looking at pistons and rods tonight.
Last edited by Little Mouse; Dec 13, 2009 at 05:34 PM.
Thread Starter
Racer
Joined: Dec 2008
Posts: 300
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From: Toms River NJ
thats why I'm asking. so I can calculate where my pistons and rods need to be. Then I can buy rods of the correct length, and pistons of the correct compression height.
Le Mans Master
Joined: Apr 2006
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were the case you just start whacking off the deck you see the problem.
.050 longer stroke the piston will go down at the bottom of the cylinder .025 further and end up .025 higher up at the top.
Last edited by Little Mouse; Dec 13, 2009 at 06:45 PM.
Race Director
Joined: Dec 1999
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From: Forked River NJ
They may be just decking it to square it up also. Sometimes the deck is uneven or warped. I know mine was terrible, probably should have started with another block but I didn't. Yes they should wait to see where the pistons are going to end up also.
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Thread Starter
Racer
Joined: Dec 2008
Posts: 300
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From: Toms River NJ
I'm currently running a 3.800 stroke, and I'm keeping it b/c its a $1200 crank. Its the crank that comes in the GM crate HT383. GM and sealed power make specific pistons just for this crank that are hypers with a 1.400 comp height, and use a 5.7 rod.
yeah, they would just be squaring up the deck. .005 to .010 ?
yeah, they would just be squaring up the deck. .005 to .010 ?
Last edited by dp9; Dec 13, 2009 at 07:19 PM.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
lota shelf-stock pistons in 1.062" ch ... 1.9" + 1.062" + 6" rods = 8.962" ... so tell em to take about 0.025" off deck ... run any 0.038"-0.040" gasket. Check w/ Ross, Diamond, CP, Wiseco etc ... maybe Mahle.
as HT383 3.8" GM crank is 1pc rms ... seems block also 1 pc rms ... so cannot be OE numbers match C3 block.
as HT383 3.8" GM crank is 1pc rms ... seems block also 1 pc rms ... so cannot be OE numbers match C3 block.
Last edited by jackson; Dec 13, 2009 at 07:52 PM.
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You need to go talk to them and ask them if they actually measured your current deck height at four corners or if they just looked at it or ran a straight edge across etc. So when it's done they can accurately tell you your deck height. Tell them you want it documented.
Then you look at gaskets available and your pistons and do some calculations as to how much you want it decked for compression and squish. For example they can clean it up at .010" but you might be better of with your piston selection and gasket choice to have the go to .015 or whatever you want
Then you look at gaskets available and your pistons and do some calculations as to how much you want it decked for compression and squish. For example they can clean it up at .010" but you might be better of with your piston selection and gasket choice to have the go to .015 or whatever you want
Le Mans Master
Joined: Apr 2006
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lota shelf-stock pistons in 1.062" ch ... 1.9" + 1.062" + 6" rods = 8.962" ... so tell em to take about 0.025" off deck ... run any 0.038"-0.040" gasket. Check w/ Ross, Diamond, CP, Wiseco etc ... maybe Mahle.
as HT383 3.8" GM crank is 1pc rms ... seems block also 1 pc rms ... so cannot be OE numbers match C3 block.
as HT383 3.8" GM crank is 1pc rms ... seems block also 1 pc rms ... so cannot be OE numbers match C3 block.
A 1.062 piston must be for a 3.875 stroke crank.
1.937 + 1.062 + 6" = 8.999
Last edited by Little Mouse; Dec 13, 2009 at 10:09 PM.
Thread Starter
Racer
Joined: Dec 2008
Posts: 300
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From: Toms River NJ
ive got an enormous spread sheet goin with all common pistons from 1.062 to 1.560 and rod combos (5.7, 5.85, 6, 6.125), dif deck heights btwn 9.025 and 9.000 and gaskets from .015 to .041. There are only a few combos that work: 5.85 rod + 1.26 or 1.25 C/H piston = 9.015 or 9.016; 6 rod + 1.062 C/H piston (as mentioned by jackson) = 8.962; or 6 rod + 1.125 C/H piston = 9.025.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
Drifting
Joined: Dec 2005
Posts: 1,360
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From: NORTHEAST
Any one boring off the decks should square the decks first so the bores are square to the main line and not square to the decks as we have seen blocks off from front to rear up to .018
I have seen blocks ruined because they were not bored off from a squared deck.
We have seen a 9.038 deck before.
Their are shops out their that can bore off the main line and not the decks.
Hell GM bores of the pan rails and their alot closer then most decks are from what I have seen.
I have seen blocks ruined because they were not bored off from a squared deck.
We have seen a 9.038 deck before.
Their are shops out their that can bore off the main line and not the decks.
Hell GM bores of the pan rails and their alot closer then most decks are from what I have seen.
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
Agree, tho it's a sound practice, I'd rather not deck a matching numbers block.
However, whenever I have one decked, my preference is to deck it the minimum amount required to square and equal it up (re-chamfer everything as needed), see how the bores clean up, and THEN order the pistons, specifying their compression height (pin CL to piston deck) to work out using a commonly available rod length. No, I never order slugs without knowing the deck height.
Note that I'm putting longer than OEM (though a commonly available length) rods in the BB I'm currently on, but since I rarely use off-the-shelf pistons anyway, extra cost is a non-issue. That said, I have rarely used special custom length rods (if that's what you indeed meant), and IMCO would never consider such in less than an all out effort racing mill. My $.02
TSW
However, whenever I have one decked, my preference is to deck it the minimum amount required to square and equal it up (re-chamfer everything as needed), see how the bores clean up, and THEN order the pistons, specifying their compression height (pin CL to piston deck) to work out using a commonly available rod length. No, I never order slugs without knowing the deck height.
Note that I'm putting longer than OEM (though a commonly available length) rods in the BB I'm currently on, but since I rarely use off-the-shelf pistons anyway, extra cost is a non-issue. That said, I have rarely used special custom length rods (if that's what you indeed meant), and IMCO would never consider such in less than an all out effort racing mill. My $.02
TSW
Last edited by TheSkunkWorks; Dec 13, 2009 at 10:52 PM.
Le Mans Master
Joined: Apr 2006
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ive got an enormous spread sheet goin with all common pistons from 1.062 to 1.560 and rod combos (5.7, 5.85, 6, 6.125), dif deck heights btwn 9.025 and 9.000 and gaskets from .015 to .041. There are only a few combos that work: 5.85 rod + 1.26 or 1.25 C/H piston = 9.015 or 9.016; 6 rod + 1.062 C/H piston (as mentioned by jackson) = 8.962; or 6 rod + 1.125 C/H piston = 9.025.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
.if you have a 3.80 crank use the 1.062 pistons ment for a 3.875 crank your going to have to cut a lot off your block if you want things nice.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
My brand new $2300 Motown 400ci block needed to be decked, it came in at 9.035", supposed to be standard OEM deck height until you reed the real real small print. 
That's why I say get them to measure the deck height, if they can't give you the numbers take it somewhere else. Just decking it so it is square is fine but you know what you a dealing with in the first place and the exact measurements after decking then go from there.
That's why I say get them to measure the deck height, if they can't give you the numbers take it somewhere else. Just decking it so it is square is fine but you know what you a dealing with in the first place and the exact measurements after decking then go from there.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
ive got an enormous spread sheet goin with all common pistons from 1.062 to 1.560 and rod combos (5.7, 5.85, 6, 6.125), dif deck heights btwn 9.025 and 9.000 and gaskets from .015 to .041. There are only a few combos that work: 5.85 rod + 1.26 or 1.25 C/H piston = 9.015 or 9.016; 6 rod + 1.062 C/H piston (as mentioned by jackson) = 8.962; or 6 rod + 1.125 C/H piston = 9.025.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
The block isnt at the machine shop yet, so nothings been done. Ill make sure I get full documentation on everything they do. I think I may tell him to leave the deck alone and go with the 6" rod and 1.125 CH pistons right at zero deck. (I'm gonna get yelled at for this one) Even if they take .010 off and the pistons are out of the hole .010, with a .042 head gasket I'll have .032 squish, which is acceptable.
Thread Starter
Racer
Joined: Dec 2008
Posts: 300
Likes: 0
From: Toms River NJ
Little Mouse: ook, I was a little confused by your earlier comment. I got it now.
Motorhead: Yes, I will def make sure the shop is doing what I want, and showing me that they did. good looking out. And i WANT to just deck to square it up. BUT if i go with any combo other than 6" rods and 1.125 CH = 9.025 I'll have to deck the cr*p out of it (8.99) to get squish anywhere near .040". Also, good call on the motown block, i really like their stuff.
Jackson: I'm glad someone else thinks .010 out of the bore is ok too.
Motorhead: Yes, I will def make sure the shop is doing what I want, and showing me that they did. good looking out. And i WANT to just deck to square it up. BUT if i go with any combo other than 6" rods and 1.125 CH = 9.025 I'll have to deck the cr*p out of it (8.99) to get squish anywhere near .040". Also, good call on the motown block, i really like their stuff.
Jackson: I'm glad someone else thinks .010 out of the bore is ok too.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Don't get too caught up with .040" squish, a little overrated in my opinion, it get very hard to do with high lift solid roller cams, mines over .040" and it makes plenty of power.