From: Barry Lovelock
Date: 27/12/99
Time: 2:30:49
Remote Name: 194.168.73.15
It's cold in that garage! I measured an unmodified Mk1Supaloy, a Modified Mk1 Supaloy and an unmodified Late Ruby head. Combustion chamber volumes were:- Mk1 unmodded 34cc, Mk1 modded 27.5cc and Late Ruby 36cc. This gives the following compression ratios with a standard 747 bore size:- 7.8:1, 6.49:1 and 6.18:1, the last two very close to the published ratios for the latter two heads. Thickness of heads (height) was 1.422, 1.500 and 1.509 respectively (first one planed) and available valve travel (chamber depth) was 0.325, 0.422 and 0.375". With a 60 thou rebore (790cc), the ratios go up, not down, to 8.18:1, 6.8:1 and 6.5:1. The standard Austin lift is about 0.250 I believe, my modified cam gives 0.3125, but with big valves, the chambers have to be heavily modified; my Late Ruby head broke though a weak spot and I had to fix it. With this head (80 thou off), I suffered from head gasket failures, due to using the standard gasket on the water branch. Leave this off and don't use one at all here. I actually use a 16 gauge copper head gasket and a similar one for the water branch. This also lowers the compression slightly. Hope this helps you to understand the problems. Barry.