On Sat, 23 Nov 2002, Richard Seaton wrote:
> I have a 1969 TR6 which had the head shaved when rebuilt ,but I don't know how
> much was taken off 15 years ago. Is there a way to measure the thickness of
> the head and to come up with some sort of compression figures?
Yes - you need to "cc" the head.
To be honest, just shaving the head "x" amount will yield a compression
increase, but the compression ratio is exactly that - a ratio. And it is
the ratio of the volume of the cylinder to the volume of the combustion
chamber (plus the head gasket thickness).
You could say that a head shaved to 3.375" is a 10:1 head, but you could
be off by a few tenths of compression if the motor was overbored .030" or
the block was "decked".
You need to take everything into consideration.
Now - cc'ing the head just means that you you a calibrated device to
measure how much liquid is needed to full to combustion chamber. You then
divide the volume of the cylinder with that number and come up with the
CR.
The volume of the TR6 cylinder (stock bore) is about 410 cc's, so with a
combustion chamber of 41 cc's, you'd get about 10:1. Similarly, 38 cc's
would be about 11:1 (actually 10.79:1).
Now, if you overbore to .030 over, your new cyl volume is about 420 cc's.
Matched to the same combustion cmaber above, the 41 cc cyl head would now
yield 10.25:1 (with some rounding up) and the 38 cc head would yield about
11.25:1.
The stock leate heads (7.75:1) have combustion chamber volumes in the 53
cc range, and the higher compression earlier cars are in the 48 cc range.
You need to pay attention to everything when doing the calcs.
Note - I did the calcs on some numbers that I had to extrapolate, but the
general relationship of the numbers should hold true.
At one time in the past, there was an excel spreadsheet floating around
that had all this stuff spelled out - but I can't seem to find it anymore.
> TIA
>
> Richard Seaton
> RSH17@msn.com
> View My restoration @ (http://groups.msn.com/Richards69TR6Restoration)
regards,
rml
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