Reply to "Cylinder head identification."

> I believe that it was in a Super Ford, circa late 80's early 90's.

I recall reading it once upon a time and dismissing it but I don't recall
the details. I've still got all my Super Fords around here someplace...

> Also what is the signifigance of testing head flow at 28in-mg? At exactly
> what rpm does one achieve that pressure?

Inches-milligrams isn't a pressure measurement. Flow bench pressure drops
are usually expressed in inches of mercury (e.g. 10" Hg) or inches of water
(e.g 28" H2O) because those are the two most common substances used in the
manometers. 10 and 28 inches of water are the two most popular pressure
drops used on commercial flow benches like a SuperFlow 600. The 28" drop
takes a larger, more expensive pump, so many measurements are taken at 10"
and then converted analytically to 28". Those numbers are generally
optimistic (compared to actually testing at 28") because the character of
the flow can change at varying pressure drops. Neither value is meant to
replicate a specific RPM and both are well below the levels (upwards of
190" H2O) that may be seen in a running engine. There are other limitations,
of course. A flow bench maintains a steady pressure drop while a running
engine has unteady flow that also changes direction (reversion). Thermal
effects are ignored and intake ports are usually flowed without an intake
manifold and exhaust ports without headers. Also, dry air is usually flowed,
instead of fuel-air mixure. Some cylinder head development (AMC, I
believe) has even been done using benches that flow water, not air.

Dan Jones