Greg wrote,
>Great.. more fun with the calculator..
>
>It depends a bit on the deck height but here goes:
>
>40 thou over = 1767cc, = 441.8cc per pot
>
>std combustion chamber =38.6 cc
>head gasket = 4.1cc
>land volume = 0.6 cc
>volume above piston at tdc = 2.0cc (assuming piston to deck distance at
>tdc = 0.015 inch
>
>total combustion volume = 45.3 cc
>
>C/R = (441.8 + 45.3)/45.3 = 10.8:1
I was very interested in replying to this thread, but until now have been
most busy.
Gregs math is correct, although my own measured volumes differ slightly.
Heres my take...
The rootes alpine head is not great at flowing due to the intake and exhuast
flow being impeded by the combustion chamber walls.
This can be helped by relieving the walls around the valves, which is the
premise of the Holbay setup.
Several CCs of chamber material must be removed to accomplish the
deshrouding
which unfortunatly leaves us short on compression. This is why the holbay
setup
only has 9.6/1 compression ratio.
This said, it is apperant that in order to achieve the maximum compression
ratio, while making the head flow well, we must remove volume where ever we
can.
I burrette measured the raw chamber volume of a rather new head at 38.0 CCs.
I area measured the stock head gasket, and extrapolated its compressed
volume to
be 3.7 ccs.
Since I was tryning to reduce the volume as much as possible (without
skimming)
I altered the compression height of the piston (design parameter) so that
not only
was all deck distance taken up, but a negative .005 inches of piston
protrusion
into the gasket volume was provided.
So here is what I cam up with.
Cylinder displacment (uses 82.5mm psitons =+.037")
= 441.3 CC
Reworked combustion chamber = 42.0 CC
Head gasket = 3.7 CC
Piston protrusion = -.68 CC
--------------------------------------------
Net Volume = 45.02
C/R = 10.8/1
Also if its a rock stock head you are after "no rework" your net compression
ratio
with my spec'd pistons will yield 12.05/1.
The net CR is the same, but you gain the added flow capablities that would
assist in higher RPM opperations, gaining HP all else the same.
Jarrid Gross
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