Aaron, the nominal deck height of a standard 318 Magnum is 9.595". It is the
same for the Magnum 360's and the 3.9L V6 Magnum as well. It scares me that
you're using a machine shop that doesn't even know the deck height on the
engine they're machining for, but oh well. As far as milling the heads, I'm
not sure what you'd need to take off the heads to acheive your desired
compression ratio. Best I remember, Magnum heads are 60cc chambers. It's not
an exact formula, but as a general rule of thumb for every CC you remove
from the combustion chamber, you can add one point to your compression
ratio(EX: 60cc head with a CR of 9.4:1, take it down to 58cc's and the CR
jumps to 9.6:1). Now, as for your compression ratio figures- the formula you
used is not right. The actual compression formula requires some specific
measurements and a long equation. I'd tell you to ask the machine shop to
help you figure it, but I doubt they'd know how after the deck height thing.
If you want to figure it out by yourself, let me know and I'll write up the
formula and you can try and find the measurements needed. The 165 psi figure
they gave you is cylinder pressure, not compression. HTH,
Will Coughlin willcoughlin@hotmail.com
'00 Reg. cab 2wd, 4.7L/NV3500HD/9.25" 3.92 sure-grip
----Original Message Follows----
From: "Aaron Gasparich" <acg302@ptd.net>
Subject: DML: engine compression.
Date: Thu, 13 Dec 2001 21:41:20 -0500
Well, i'm finally assembling my engine. But i'm trying to figure out what
compession i need to up to to match my hughes 1418 cam. I know that hughes
says it need to be at 165psi. if normal air is at about 14.5psi@sea level
than 165 translates to about 11:1, is this true? I think I could figure it
all out on my own if i knew the deck height of a 318, but since I
dont(neither does the machine shop) I have to pose the question. Is the
stock 9.2:1 compression ok on this cam, or will i have to mill the head a
few thousandths to achieve a higher compression and the benifits of the cam.
Does anybody know the deck height of the 318? I feel a little bit lost here
when it come to the compression part of an engine. And if i need to shave
the heads, does anybody have an idea as to how much i need to take off?
Thanks to everybody for the help
-Aaron
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