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Old 05-14-2010, 08:53 PM
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Compression Ratio?

I've posted this on a couple other forums and no one seems to really know the answer. I have gotten anywhere from 9.2-10.5 for answers so...

I have a 460 short block out of a 1976 Thunderbird I will be running D0VE heads on. I am trying to figure out about what my compression ratio will be.

the motor looks like this:
'76 stock short block
worked D0VE heads with Stainless 2.250/1.725 valves
1.73 roller rockers
Lunati 61604
Performer RPM intake
2" Hooker swap headers
Canton oil pan kit
Holley 850 D.P.

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Old 05-14-2010, 10:35 PM
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Need to know:

bore and stroke
deck height
combustion chamber volume
gasket volume
piston type, volume in cc's to account for dish, dome, valve relief etc

I think that's it, it's difficult to figure out compression unless most or all of this info is avail.
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Old 05-14-2010, 10:38 PM
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You forgot gasket bore size unless your counting gasket volume as thickness and bore size.
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Old 05-15-2010, 07:36 PM
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OK, to figure static compression ratio, you need 5 figures, cylinder volume, combustion chamber volume, piston crown volume, head gasket volume and piston deck height volume.

If we know that the '76 Ford 460 motor produced only 202 horsepower, then we can assume the stock static compression ratio was abysmally low. We can further assume that the cam timing was very short. We also know that the combustion chambers of these mid-seventies 460's was around 96cc's and that the D0VE chambers are probably around 76cc's.

So, if we use 942cc's in the cylinder, 96cc's in the chamber and assume 10cc's in the piston, 10cc's in the gasket and 10cc's in the piston deck height, then we have a total ingested of 1068cc's and a total squeezed of 126cc's. Dividing the smaller into the larger will result in a 8.47:1 static compression ratio. That's probably pretty close to right, given the low hp rating.

Now, if we change the heads to ones with 76cc chambers, we change the ingested to 1048cc's and the squeezed to 106cc's. Dividing the smaller into the larger will result in a 9.891 static compression ratio.

That's about the best I can do by the seat of my pants and without any real data to go by. The problem with doing this will be that the short cam timing will not support the increased static compression ratio and the motor will rattle like a can full of marbles on pump gas for a while, until it holes a piston. Then the game is over.
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Old 05-16-2010, 03:42 PM
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i personally like it when you revv a 460 to 6800 in a jet boat, you come out of the water, hit 7 grand and it spits a pushrod through your cam,cam drops into the rotating assembly, cracking a water jacket...

anyone interested in a distributor less 3/4 race cam?
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