The Tulsa Club did extensive testing of various stock and aftermarket heads, including the "Z" head. At that time the "Prus" head was not available for testing. Has anyone done any unbiased comparison testing ,or have any unbiased test figures that can be compared to the Tulsa club's tests on the "Z", to see which one makes the most power?
Tom Graham did a dyno test comparing a Prus and a Z head on the same engine in 2012, see this thread:
Low end torque about the same but the Prus head gave 2hp more at the top end = 28hp versus 26hp for the Z head. The compression is about equal for both heads but the Prus head follows the Ricardo priciple better - that's the likely cause for the difference.
Z gets "Ford" and "Made in USA" markings; in alloy only.
P is correct for 26-27 cars (NO "Ford" or "USA" markings); in alloy AND iron.
People have reported issues with using the P with low octane fuel. ???
I've used a Z will 80 octane fuel without problems.