In a message dated 5/22/00 7:53:01 PM Pacific Daylight Time,
toplessdatsun@ga.prestige.net writes:
<< Um, who suggested that you do that? With a perfect 2l head
(never cut) and not correcting for material you may have removed
from the head to clear the pistons, a quick calculation
indicates about 12:1 CR. Are you planning on running
racing fuel?
Jim >>
Back in the late 60s. I had my 67.5 U20 engine assembled by Bob Sharp. they
used domed R16 pistons and "flycut" reliefs for the valves(Solex B cam). By
the way, times have really changed, I have the bill in front of me and the
pistons were $5 each! The head was cut around .010" and the engine was bored
.040 over. To the best of my recollection the compression ratio was in the
very high 12s. Would only run without detonation on Sunoco 260 gas(103
octane). By that time the Sharp team was using 100/145 octane avation gas.
The combination of the high compression and advanced timing was too much for
the starter motor. I had to put in seperate ignition and starter switches..
get the engine turning with the ignition off and then hit the switch to
start.
This engine didn't last too long, and the next one that Sharp assembled got
the U20 flat top pistons, and the head cut .070. With .040 bores and
combustion chambers at 36.5cc plus 10cc for the piston and head gasket area
the compression ratio worked out to 11.7:1, much more livable.
Jerry Krakauer
SRL311 00099
|