Packard Forum Index » V-8 (1955-56)

I'll go back down and check, but I could plainly see the screw head image on the left of the number to hold the number plate on the mold. Perhaps the "D" is not actually a D but the other screw head holding the plate on the right side?

Mine also says "CD" and both screw heads are plainly viisible.
Thanks Dave for correcting this.

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PackardV8 had it right. Service Counselor Vol 29 No 7 speaks of Cast Dome cylinder heads for the 320 cubic inch engines and states that the heads will be marked "440584 CD". They probably later applied the same technology to the heads on the large engine and marked the heads with CD to designate same.

G'day Boys, I haven't contributed much lately but thought I should throw some small change into this topic. I can't tell you what numbers are on the heads of my '56 Patrician (body & engine # 5682 3692) until I can get back out in the shed (just had knee surgery this afternoon). What I can tell is that for quite a few years now I have been running NGK BPR5EY plugs in my car and have had no trouble whatsoever - just clean and regap every so often and all is good. By the way, if I remember correctly the "Y" in the number relates to a notched centre electrode which is supposed to divide the spark and give a better burn. Cheers, John

G'day John,

All the best with the knee. See you in South Australia at the Packard National Rally next month!

Cast Dome is a new term for me, perhaps either a way to save some machining costs in a tough financial crisis, or just a better way to shape a more efficient combustion process. I'll add this to my list of changes made to these cars between 1955 and later 1956s. Not having access to the cited Service Counselor bulletin, is there a reason or benefit given, and what mention is made for the spark plugs being changed?

Just like the early and late 1963 Corvettes being distinctly different parts animals, was there a watershed production change when 1956 cars turned into something else? Or did running changes comprise most of the differences between early and late?

I haven't checked but I'm assuming that Service Counselor is on line here so you can read all the details; hard to scan from a bound volume but here's a snapshot. The change to cast dome combustion chamber also involved changes to the distributor (timing, advance curves), carburetion, and spark plugs (reach changed from 7/16 to 3/4).

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Was worried that Packard could have sold leftover '55 engines to AMC for '56, but that was not the case, as number is 6480406 CD on middle exhaust port.

What about these.. 14 m but only short threads..

I tried to torque them to 25 lbs but didn't. Feel right.

So put them in at 10 lbs

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