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Best way to find compression with engine in car?

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Old Dec 24, 2013 | 09:13 AM
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Default Best way to find compression with engine in car?
I'm unsure of the compression in my 408 and would like to 100% positive what it is for future reference.The motor is in my car and running fine.
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Old Dec 24, 2013 | 09:22 AM
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U would need piston info. And cylinder head cc to come up with compression. May have to remove head to find this out.
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Old Dec 24, 2013 | 09:23 AM
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Do u knoe any specs on it at all? What heads?
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Old Dec 24, 2013 | 09:30 AM
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Originally Posted by (SS)
I'm unsure of the compression in my 408 and would like to 100% positive what it is for future reference.The motor is in my car and running fine.
To known 100%, you would have to pull the heads and measure everything.
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Old Dec 24, 2013 | 09:55 AM
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Originally Posted by brandon6.0
Do u knoe any specs on it at all? What heads?
I have a set of ported 317's(lightly)
The cam is 252/256 612/612 112
The bottom end is a forged/stroked 408 at 10:5 to 11:1 compression

This is the info i got from the previous owner
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Old Dec 24, 2013 | 09:58 AM
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Originally Posted by KCS
To known 100%, you would have to pull the heads and measure everything.
Even without knowing what pistons are in the motor?
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Old Dec 24, 2013 | 10:13 AM
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With the heads pulled you could figure out at least pretty closely what the piston volume is.

Why do you need to know? A cranking compression test wont tell you what the ratio is but can give some idea of how aggressive the compression ratio is when the cam is considered also.

Don't get me wrong, I would want to know what the ratio is too but I am just trying to help you come up with a workaround that doesn't require dissassembly.
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Old Dec 24, 2013 | 10:21 AM
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Originally Posted by (SS)
Even without knowing what pistons are in the motor?
When I wrote everything, I meant everything. You would want to measure the bore, stroke, volume of the reliefs and/or dish of the pistons, piston deck height, chamber volume, and head gaskets dimensions.
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Old Dec 24, 2013 | 10:52 AM
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Originally Posted by KCS
When I wrote everything, I meant everything. You would want to measure the bore, stroke, volume of the reliefs and/or dish of the pistons, piston deck height, chamber volume, and head gaskets dimensions.
That's what i was afraid i was going to have to do to be 100% correct,because as far as i know it could be a stock 6.0.
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Old Dec 25, 2013 | 09:41 PM
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Pull one head and check. Almost worth it when buying a complete used motor. U never know until u do.
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Old Dec 25, 2013 | 09:42 PM
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Its only up to you. Nothing we can really do to help unless u do.
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