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Cylinder head thickness vs. comp ratio

To: Triumphs Mailing List <triumphs@autox.team.net>
Subject: Cylinder head thickness vs. comp ratio
From: Pete & Aprille Chadwell <pandachadwell@mac.com>
Date: Tue, 15 Jan 2002 13:30:28 -0800
I'm curious about something.  I'm wondering about figuring out 
cylinder head thickness specs for certain 'target' compression ratio 
figures.

Years ago I acquired a TR6 motor whose cylinder head had been heavily 
shaved, but I didn't have any way to know what the compression ratio 
was.  So, using a little algebra (wouldn't my math teachers be 
proud?) I figured out what the compression ratio for that head should 
be based on its thickness as compared to Kastner's measurements for 
10 or 10.5:1 and based on the stock thickness spec.  According to my 
figures, that cylinder head has a compression ratio of 11.8:1.  Ouch! 
No wonder the ring lands on the pistons had shattered!

That all seems convincing enough, but the trouble is I don't know if 
the relationship between head thickness and compression ratio is 
linear.  If it's not, then I don't think my numbers are accurate. 
Despite all that figuring, I really and truly belong in the home for 
the mathematically challenged, so I can't guess as to whether that 
relationship should or should not be linear.  Anybody know if you can 
extrapolate from known specs to get thicknesses for a given 
compression ratio in this way?  Assuming my arithmetic was correct 
all those years ago, should my 11.8:1 figure be correct?

-- 
Pete Chadwell
1973 TR6

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