[TR] Compression Ratios TR250 Heads

[Randall]

> This claim seems to omit the
> oversize bore as a function of compression?  Confused about that. Also
> what if
> the block has been decked?  Should I inquire?

Darrell, I can't answer the question about TR250 head vs early TR6.  But I
would treat the compression claim with a large grain of salt, for exactly
the reasons you mention.  Both the overbore and the block decking (if any)
will increase the compression ratio, unless something is modified to bring
it back down.  If the block has been line-bored, that may also affect piston
height, and in turn compression.  Plus of course, it may have even been off
somewhat from the factory.

> Also I have asked for a stock grind on the camshaft.  Would that  profile
> effect compression?

The camshaft profile will not alter the compression ratio; although it may
change the number read with a compression gauge.  However as a very rough
rule of thumb, a 'performance' camshaft will usually cause the engine to
tolerate a higher compression ratio better.

> Too many
> choices
> and I don't want to regret what get's done so I would  appreciate the
> advantage of having the wisdom of the List.

Personally, what I would do (given your goals) would be to look into having
the combustion chambers opened up a bit, to bring the compression back down
to 9:1.  That should be plenty low to let you run on pump gas, and require
relatively little modification to the head.  Again I'm not familiar with the
TR250 head, but certainly on a TR3, the chamber can be improved
substantially that way. 

BTW, your idle problems before were almost certainly due to factors other
than compression ratio.  The camshaft is the biggest tradeoff between smooth
idle and high performance; a high compression engine with a stock camshaft
should still idle just fine.

Randall