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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: head machining
Randy Wilson:
> > BTW, with the Mays head design, you would have to mill a very large
> > amount off the bottom to have an impact on the compression.
The Mays head design should be the MOST CRITICAL in this regard. Since the
compression ratio is relatively high, that means the combustion chamber is
relatively small -- hence changes resulting from milling make a larger
percentage impact.
> From: "pcsolutions" <pcsolutions@mindspring.com>
> I would also imagine that if the head in question was machined to a
> such an extent to affect compression ration that drastically, it
> would be impossible to adjust the timing chain slack.
I dunno what you guys are thinking. The volume of a 5.3 V-12 cylinder is 442
cc. With an 11.5:1 compression ratio, that means the volume of the
combustion chamber is about 42cc. If you mill 20 thou off the mating
surface, this volume will decrease by 3.23cc -- increasing the compression
ratio to 12.4:1. This is a significant change, and anyone doing such engine
work should know this. And if the block is warped and one cylinder gets
shaved more than another to make it flat again, the compression ratios can be
significantly different from cylinder to cylinder. cc'ing the head is
mandatory when doing such work.
It should be noted that valve work can have similar (possibly opposite)
effects. If the seats of valves are reground, the valve sits deeper -- and
the volume of the combustion chamber increases, and the compression ratio
goes down.
-- Kirbert | If anything is to be accomplished,
| some rules must be broken.
| - Palm's Postulate
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