Greg tossed out, in part:
>
> Patrick Golder states in a previous posting that boring out an engine will
> not increase compression ratio.
> Well, seeing as I have nothing to do but sit behind a PC, I ran the
> math.
> The compression ratio was increased in my model (Triumph 2000cc 6-cyl) by
> .10, after a boring out of .030 inches. The cylinder head volume was left
> constant.
Ah, but you are making the assumption here that the maker of your 030 pistons
used exactly the same piston pin to crown height as the std bore.
> Interestingly enough, if I bored out the cylinder head combustion chamber
> along with the cylinder itself, the compression ratio remained the same.
>
On a large number of engines, a substantial part of the combustion chamber
is actually in the cylinder. This part would have been bored, thereby lowering
the compression. An extreme example of this would be a Jag V-12 with their
flat faced heads. All of the combustion camber is in the cylinder area.
> As a note, work output of a piston cylinder is given by the theoretical
> equation P*V, where P is pressure, and V is Total Volume. (heat and frictional
> losses neglected). Increase either or both, and work output (Torque) will
> be increased. From this it is evident that head milling is a compromising
> modification, while cylinder boring is not.
I don't follow you on the "compromising" part. Raising the compression
ratio raises the working pressure. Milling the head is sometimes the best
approach for minor compression increases. Though, with most engines, milling
the block yields much better results. I guess the reason the heads get milled
so often is a matter of convenience. Much easier to pull the head than to
pull and strip the block.
Randy
randy@taylor.wyvern.com
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