Reply to "Compression ratio"

> I am thinking of rebuilding my 351C using Aussie 2V heads and a
> Ford SVO cam. What compression ratio can I get away with running
> on pump gas.

The Ford SVO hydraulic cam is a dual pattern (214/224 @ 0.050",
0.510"/0.536" lift, with 112 degrees lobe centers) flat tappet cam.
Given those specs, it is best suited to a relatively mild open
chamber 4V engine. BTW, Ford has dropped that grind (and all cams
for the Cleveland), though you can find similar grinds from other
cam companies.

For most applications, the closed chambered Aussie 2V heads work
best with a single pattern cam (with equal intake and exhaust lift
and duration) and 110 LSA angle. The best duration and lift for a
particular application depend upon the rest of the parts used and
what you plan to do with it.

The maximum compression ratio you can run is dependent upon several
factors but suffice it to say that there are a lot of us running
closed chamber heads with flat top pistons on premium pump gas (92
or 93 octane around here). If you polish the chambers and unshroud
the valves in the Aussie 2V heads and run a bit of cam, you can get
along just fine with quench heads and flat top pistons. At worst,
you'll need to dial out a little spark advance at lower RPM. It is
important to not install thick headgaskets or mill the tops of pistons
or run a circular dished pistons or any of the usual tricks for
dropping compression when you run the closed chamber heads. The flat
part of the piston needs to come close to the flat part (the quench
pad) of the head. Keith Black suggests holding the quench distance
to .040". The quench distance is the compressed thickness of the
headgasket plus the deck clearance (the distance your piston is down
in the bore). Quench heads have a flat area opposite the spark plug
and an open area around the plug. As the flat top piston rushes up
toward the head, the area under the flat reduces quicker than the
area under the open part of the head. The result is the mixture is
forced at high speeds towards the plug. The resulting turbulence
evens out temperature and more completely burns the mixture. More
power, better fuel economy, and higher compression on the same octane.
So the point is not to drop compression, the point is to maximize
the quench effect so you don't ping. In cases where you need to
run a dished piston (stroker, nitrous, or supercharged engines),
use a D-dish with the dished part of the piston under the chamber
and the flat part under the quench pad (or better yet a mirror image
of the quench chamber).

Dan Jones