Hi Rich and Folks. Glad to see some interest in my favorite subject.
It is not easy to get your hands on Facts about the original Ardun
heads. There is a large body of mythology along with the facts. Period
journalism has errors. Misprints abound.
Looking at the original company literature, it states the head castings
are Alcoa 355-T6. OK, thinks I, this is merely a misprint for the
well-known 356-T6. But no! Machinery's Handbook gives 355 as a common
casting alloy, along with 356, and very little difference between them.
So let us say that the original literature is correct, and accept the
castings as Alcoa 355-T6. The T6 means a certain heat treatment applied
(details known to experts) but I do know it makes the castings harder,
tougher and stronger, all good.
Today's repros are said to be cast of Alcoa 356-T6. Probably some
slight difference, have we any experts out there who can tell us what
the practical difference is?
The cartridge fire principle where the spark plug electrodes are up in a
little hole about 3/8" from the combustion chamber has always been
intriguing. Several Ardun greats have told me that this has no effect
on power (most of the older records were set with cartridge fire
heads), just requires more spark lead because the ignition is slowed
down. Clem TeBow recently told me at C.T. Automotive they found on the
dyno that with a Vertex mag, power was the same from 40 degrees to 50
degrees advance, so they selected 45 as a conservative figure. Every
combination is different, so your results may vary. When the cartridge
fire is deleted, as with today's repros, you use about 36 degrees total
advance, depending on fuel, engine size, compression ratio, etc.
The original Ardun heads are heavy and strong, and the general lore is
that they have survived 50 years very well, not very prone to cracks or
serious corrosion. Obviously there are a lot of them still around.
Zora told me about 300 sets were made. I imagine probably at least 200
of them are still with us, maybe more. Not something you throw out
readily.
Speedy Bill at Speedway has an Ardun repro project which has not yet
been completed. He told me that Arduns on nitro are prone to cracking
in the top of the chamber. If he meant something like 90% at
Bonneville, I wouldn't fault the heads or the designer for that, it is
far beyond the original design intentions. Ardun experts have told me
that if any cracks did arise from any cause, they cured them by expert
welding and remachining.
What connection did Ardun and the Hemi Chrysler have?? Stay tuned (if
anybody cares) for more documented speculation. Regards, ArdunBill in
Chesapeake, VA.
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