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408 8.5:1 Compression test. What readings should b expected?

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Old 12-12-2008, 05:45 PM
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Default 408 8.5:1 Compression test. What readings should b expected?

Going to do it this weekend and just wondering what numbers I should be seeing. I understand that it needs to be done at operating temps and that it aside from max compression, it matters how fast it gets there.


If I'm missing anything, feel free...


Arnel
Old 12-13-2008, 08:09 AM
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my 347 is 8.7ish and i was getting around 175-195 fyi..
Old 12-13-2008, 11:27 AM
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Originally Posted by rx_treme
my 347 is 8.7ish and i was getting around 175-195 fyi..
Thanks..

I got 160-162 w/ #8 showing 158. Thats somewhat lower than yours but I'm wondering if maybe cam and bore/stroke varies it some.

My cam is a..

Cam Motion 236/232 dur. @.50" .588/.574 114LSA 110ICL


Any thoughts on the numbers I got?


Oh, and your setup looks great!
Old 12-13-2008, 02:56 PM
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Thanks! (our cams are close to the same)
Thats just fine for compression. yea cam etc does make a difference but you just want a ballpark to tell you difference between cylinders. Also the temperature etc makes a difference.
Go buy a leakdown tester, that will tell more about your motors health than just compression.
Old 12-13-2008, 04:26 PM
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Originally Posted by rx_treme
Thanks! (our cams are close to the same)
Thats just fine for compression. yea cam etc does make a difference but you just want a ballpark to tell you difference between cylinders. Also the temperature etc makes a difference.
Go buy a leakdown tester, that will tell more about your motors health than just compression.
The compression test was done with motor at temp. As for leakdown, I actually did that first and they were pretty identical across all 8.

I'm seeing a little more blow-by at idle and generally more overall compared to when first installed.




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