Bill :
Well, Piggott gives the original CR (with 83mm liners) as 8.5, and says
the lowering kit results in 7.5. I'm told the original headgasket
crushes to about .060", and the steel gasket supplied with the lowering
kit crushes to about .020". CR is (swept volume + unswept
volume)/(unswept volume), and the swept volume per cylinder is (4.15cm *
4.15cm * 3.141592) * 9.2cm = 497.78cc.
So, unless I've slipped a digit on the calculator, the stock unswept
volume is 66.37cc, of which 8.24cc is the head gasket and 58.13cc is the
combustion chamber in the head. (I'm assuming the pistons come flush
with the top of the block, anyone know if this is supposed to be true ?)
(I'm also assuming the opening in the head gasket has the same area as
the cylinder, which isn't strictly true, but should be close enough.
And, ignoring the space between the rings and the top of the piston,
which should also be too small to matter.)
At 7.5CR, the unswept area must increase to 76.58cc. Subtracting the
combustion chamber volume leaves 18.45cc, which for an 83mm hole would
be 0.134". Subtracting .060" for the stock headgasket, and .020" for
the steel gasket, leaves 0.054" for the plate. (Again assuming the
openings in the gaskets and plate are 83mm in diameter, which may not be
correct.)
The CR you get with Mordy's head gasket will depend on your selected
bore size, but the info above should let you figure it out. Remember,
the area of a circle (the top of the piston, etc.) is Pi (3.141592)
times the radius squared (the radius being half the diameter), and
volume is area times height. Put everything in centimeters first, and
the rest is easy (it must be true, says so right here in my book <g>).
Of course, if you're building a hot engine, you're probably using the
late TR4A head, which bears no resemblance to the numbers above ...
And last, I screwed up the CR on my engine (got it too high), so maybe
you shouldn't trust anything I say ... <g>
Randall
59 TR3A
bill williams wrote:
>
> anyone know a formula that would
> tell me how much a 1/8 inch head gasket would lower
> the compression ratio??? AND does anyone have any old
> factory info that tells how thick the compression
> lowering kit was..and how much IT would lower the
> compression ratio??
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