Message text written by "Randall Young"
>I'll let others comment on the effect of mixing components, as I just
know that much about the 6-pot. But according to Piggott, the HE engine
never more than 9.5:1; and if I run the above formula backwards then
forwards (assuming a 7.47cm bore & 9.5cm stroke, also from Bill), I get
a .020" overbore will increase it to a whopping 9.6:1. Of course I am
a Pentium ... so YMMV <g>
My HP 32S confirms the calculations so rest easy.
The heads are interchangeble but the early CC heads need the early intake
manifold and the later CF heads need the later intake.
The recommended procedure to determine compression ratio is the "cc" the
head. Assuming the valves don't leak and the spark plug seals well, mount
the head upside down and as near perfectly level and using a graduated
cylinder, determine how much fluid it takes to fill the combustion chamber
flush with the head mating surface. You can use whatever fluid strikes
your fancy assuming it doesn't evaporate fast enough to throw off your
measurements. This will give you the "U." Divide that into your "S"
(approx 420 cc) and you have your current compression ratio. If it comes
in near 8:1 I would recommend shaving the head when you get it rebuilt. If
it is close to 9.5:1, don't.