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Old 12-03-2009, 11:17 PM
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Deck height

If you take a SBC block to a reputable shop for a street/ strip build and the block is "zero decked", what is the new deck height? 9.025? what is actually done? Is deck height the measurement from the crank journal centerline to the very top ridge of the deck, where the manifold butts up?

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Old 12-03-2009, 11:57 PM
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Quote:
Originally Posted by Jeff The Ruler
If you take a SBC block to a reputable shop for a street/ strip build and the block is "zero decked", what is the new deck height? 9.025? what is actually done? Is deck height the measurement from the crank journal centerline to the very top ridge of the deck, where the manifold butts up?
0 Deck height will be 9.00"
Center of Crank journal to Block surface where the Head bolts on.
Be aware if you plan to or need to have the Deck resurfaced in the future, it's best not to 0 Deck the block. @0 Deck height the Piston is level with the top of Block.
You can Deck it to 9.012" and use a GM .028" thick head gasket to get .040" quench. Or 9.015" and .025" gasket for .040" Quench.

Last edited by SSedan64; 12-04-2009 at 12:05 AM.
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Old 12-04-2009, 12:14 AM
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Technically, zero deck is when you machine the deck to have the pistons flush with the deck, so depending on the piston/rod/stroke combination you use, zero decking a block could be a wide variety of measurements.
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Old 12-04-2009, 08:36 AM
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Your answer is here: http://www.rbracing-rsr.com/squishcalc1.html
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Old 12-04-2009, 12:53 PM
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Quote:
Originally Posted by Jeff The Ruler
If you take a SBC block to a reputable shop for a street/ strip build and the block is "zero decked", what is the new deck height? 9.025? what is actually done? Is deck height the measurement from the crank journal centerline to the very top ridge of the deck, where the manifold butts up?
OK for an OEM Chevy small block, the nominal measure of a production block from the crank center line to the top of the head deck is 9.025 inches. However, many production blocks are salvaged from manufacturing mistakes and the actual dimension of any OEM unmolested block may be less.

The assumption is that a zero decked block will have the head deck cut .025 inch which will at 9 inches make the head deck the same height as the piston crown. Hopefully a "reputable" shop will measure the true distance first not just bolt the block in a fixture and whack .025 inch off of it.

If you measure 1/2 the stroke, add the center to center length of the connecting rod and the pin center distance to the piston crown it should be 9 inches. Manufacturing tolerance build ups may actually measure a bit longer or shorter. You also need to be sure of the piston pin center to crown distance on replacement pistons, many pistons are made with the assumption that the block will be zero decked, so they're pin center the crown height is lowered .025 inch. If you assume your block is zero decked and you use these "production" rebuild pistons with an .040 inch thick gasket, the piston will be .065 inch from the heads squish/quench deck which will reduce these effects and lower compression below where you think it is. So make double sure of the piston pin to crown height, often called the compression height or distance.

If you're changing rod lengths the compression height also has to change to keep the total of the lengths 1/2 stroke + rod centers + compression height within the height of the block.

Milling the head deck has a similar effect on intake manifold fit as milling the heads, that is all this stuff is lower and closer together, so the intake may require milling of it's base and sides to make an air and oil tight fit. This is especially true when zero decking and head milling both are present.

So this is some stuff to be watching out for and making sure your shop is doing the same for you.

Bogie
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Old 12-04-2009, 06:02 PM
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The motor has been built for a couple years and in the car now, still havent gotten to fire it. I lost some of the papers from the machine shop that put the bottom end together, now i'm wanting to go through and make sure I know critical dimensions. Reason I started this thread was to find out more about my pistons being "down in the hole" or not, cause im wanting to determine my true CR. Now that I remember, the pistons sat flush with the deck.

Pistons are KB hypers, 7cc flat tops with 1.433 compression height. heads have 64 cc chambers. rods, 5.7

I understand from reading KB's website that dished or flat tops with reliefs add to the chamber vol. while domes subtract. makes sense.

Ive learned alot about motors from reading it surprises me but still some stuff i wanna get a handle on before I fire it for the first time. I know from buying the heads that the CR is gonna be high enough to wanna have confidence in the fuel, thats where im going with this.

Last edited by Jeff The Ruler; 12-04-2009 at 06:10 PM.
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Old 12-04-2009, 06:27 PM
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Quote:
Originally Posted by Jeff The Ruler
The motor has been built for a couple years and in the car now, still havent gotten to fire it. I lost some of the papers from the machine shop that put the bottom end together, now i'm wanting to go through and make sure I know critical dimensions. Reason I started this thread was to find out more about my pistons being "down in the hole" or not, cause im wanting to determine my true CR. Now that I remember, the pistons sat flush with the deck.

Pistons are KB hypers, 7cc flat tops with 1.433 compression height. heads have 64 cc chambers. rods, 5.7

I understand from reading KB's website that dished or flat tops with reliefs add to the chamber vol. while domes subtract. makes sense.

Ive learned alot about motors from reading it surprises me but still some stuff i wanna get a handle on before I fire it for the first time. I know from buying the heads that the CR is gonna be high enough to wanna have confidence in the fuel, thats where im going with this.
With a .040 inch thick 4.1 inch dia gasket, my home made SCR calculator gets 9.83 to 1 with your set up.

Bogie
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Old 12-04-2009, 06:55 PM
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Thanks Bogie!
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