Richard,
I just went through this exercise on my 250 motor and the shop that did the
machine work had a little PC program that calculated CR based on cc'ing a
chamber. The numbers pretty much correlate with the Goodparts numbers so I
would have some pretty good confidence in them.
With that said, you need to get to 3.416 inches, removing 0.063" in the
process. Have the machine shop CC the head to verify the volume before they
mill the head and then after. You never know what a DPO might have done.
Just in case CC'ing is an unknown term to some, it involves covering a
combustion chamber with a clear cover that has a small hole to accept fluid
from a graduated cylinder/pipette until filled. Knowing how much fluid was
in the pipette you the observe how much fluid left the pipette. That is the
combustion chamber volume noted in the Goodparts CR article.
As an FYI The first link below is a CR calculator and shows how many factors
are involved in the calculation. There are many others on the web. The
second is an actual "how to" on cc'ing a head.
http://www.smokemup.com/auto_math/compression_ratio.php
http://www.mergetel.com/~lee/73-77ag/tech/checkcc/
Greg Dito
CD6250L
----- Original Message -----
From: "Richard Seaton" <rsh17@msn.com>
To: "6 Pack" <6pack@autox.team.net>
Sent: Sunday, October 19, 2003 8:28 PM
Subject: Compression ratios and head thickness
> Hey guys I need some help from a knowledgeable source. I want to raise the
> compression on my early narrow port head ('69 TR with 8.5:1 compression)
to
> 9.5:1. I've looked at Goods sight on compression ratios and also called
TRF
> for some figures, strange thing is that what TRF spec'd out doesn't match
> Richard Good's on all thickness and CR. Does any one know for sure the
> original thickness of the head and how much needs to be shaved off to
achieve
> 9.5:1. I'm not saying Good isn't right but just need to make sure.
> Oh yeah, standard bore.
>
> Thanks again,
> Richard Seaton
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