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Old 07-16-2012, 03:05 PM
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Numbers needed to figure out compression

I'm using the Summit Calculatror for Compression:
Compression Calculator - SummitRacing.com

I am trying to figure out the deck clearnace and effective dome volume.

I don't have any measured values but I do know that the following pistons were use:
Speed Pro ZL2165F - Speed-Pro Forged Pistons - Overview - SummitRacing.com

They have a compression distance of 1.671 in. Is it posible to claculate the deck clearnace from these numbers. Stroke is 3.25, bore is 4.040.

piston head volume of +5.4cc. Is this the effective volume needed in the Summit Calculator

Thanks for your help,
Vic

Last edited by cadmanof50s; 07-16-2012 at 03:16 PM.
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Old 07-16-2012, 03:25 PM
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Quote:
Originally Posted by cadmanof50s View Post
I'm using the Summit Calculatror for Compression:
Compression Calculator - SummitRacing.com

I am trying to figure out the deck clearnace and effective dome volume.

I don't have any measured values but I do know that the following pistons were use:
Speed Pro ZL2165F - Speed-Pro Forged Pistons - Overview - SummitRacing.com

They have a compression distance of 1.671 in. Is it posible to claculate the deck clearnace from these numbers. Stroke is 3.25, bore is 4.040.

piston head volume of +5.4cc. Is this the effective volume needed in the Summit Calculator

Thanks for your help,
Vic
You need a figure for the head gasket thickness and a figure for the deck clearance. The uncut deck clearance is supposed to be 0.025", but unless you've measured it, it may have been milled during a previous rebuild. If you know what to look for, you can often tell a deck surfaced at the factory from a deck that's been resurfaced by a machine shop.

In any event, you want to try to have a 0.040" or thereabouts quench distance, regardless of the deck clearance. This can mean you will need to cut the block deck a minimal amount and use thin, shim-type steel head gaskets or cut the block decks more in order to use a thicker composite head gasket.
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Old 07-16-2012, 03:55 PM
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OK...thanks for the info.
I'm still not 100% clear, though.

When I replace the heads, I want to know which gasket I need to go with. I pretty much have a choice of only two thickness. .039 and .015. (Fel-Pro)

But in order to achieve the compression I am targeting (roughly 9.5), I need to know deck clearance.
From what I understand..Quench is teh distance of teh deck clearnce plus teh gsaket thickness....(maybe that is an over-simplification).

BTW, I would say that the block has not been decked. The serial number of the block is clear, and very readible. I would think decking would make this SN either very difficult to read or tak eit away completly...??

Vic
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Old 07-16-2012, 04:13 PM
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Quote:
Originally Posted by cadmanof50s View Post
OK...thanks for the info.
I'm still not 100% clear, though.

When I replace the heads, I want to know which gasket I need to go with. I pretty much have a choice of only two thickness. .039 and .015. (Fel-Pro)

But in order to achieve the compression I am targeting (roughly 9.5), I need to know deck clearance.
From what I understand..Quench is teh distance of teh deck clearnce plus teh gsaket thickness....(maybe that is an over-simplification).

BTW, I would say that the block has not been decked. The serial number of the block is clear, and very readible. I would think decking would make this SN either very difficult to read or tak eit away completly...??

Vic
The link above explains what quench is. You need to know what the piston-to-block deck clearance is- using the crank, rods, bearings and pistons you want to use in the engine. This is called the mock up phase of the build, and is where the parts are assembled temporarily to see what you have to do in order to get the correct quench distance, etc.

The only other ways to go about checking the block deck height is to measure off the crank bore centerlines (a machine shop operation for the most part) or to measure the piston-to-deck clearance w/the parts that were originally in the engine (pistons, rods, crank, bearings). By carefully measuring the piston-to-deck clearance of the front and rearmost cylinders on both sides, AND by knowing what the compression height of the pistons that are in it when you do the measurements, you can get an idea of whether the deck has been cut and whether the block is square or not.

It's safe to assume the block will need at least a light cut to get the decks flat, and a light cut is also needed to get a shim-type HG to seal (like your 0.015" gasket). If you want to use the 0.039" composite HG, the decks will need to be cut to "zero" or close to it. Zero decking the block is when the top of the pistons are even w/the block decks.
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Old 07-16-2012, 04:16 PM
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Based on the piston pin heght spec 1.671 and the block being standard 9.025"
I get 9.66:1 using a felpro .015" gasket and 64cc heads and 5.7" rods
4.04x3.25

The piston would be .029" in the hole @TDC. (assuming the block is 9.025")

I would measure the actual piston pin height and installed deck clearance.

GM sells a .026" gasket too.
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Old 07-16-2012, 04:27 PM
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Thanks for the info, guys.

Once its appart, I will do an actual measurment, for sure.

F-BIRD that's within the range of what I'm after.

Vic
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