Kevin, you can go with R45S for short reach, with gasket, or R45XLS for long reach, with gasket. If I remember right, my '55 320 in the Pat takes the long reach, and it's the machined dome, so I'm thinking the Cast Dome heads take the short.

Frankly I'm reluctant to rely on old plug recommendations as the changes in gasoline composition, flame temperature and propogation have changed so much. So I usually take a current recommendation from one of the plug makers. Autolite's site is among the easiest to use, and for my 56 Packard they recommend Autolite 66 for a non-resistor plug (my choice). I've also used Champion RN14YC with good luck. You don't say if your upgrade of a 55 to a 56 V8 involved changing heads but I guess you know there were different plug requirements when they went from machined to cast heads (see Service Counsellors for info). If I still had the 55 heads, I'd hop onto Autolite's site and get their recommendation for 1955.

R45LS, two steps hotter.

Thanks Owen,

As I mentioned I pretty much bought those plugs on impluse. Can you please recommend & provide a quick listing of plugs that will work in my Packard V8. If it matters, I have a '55 block that has been rebuilt to '56 374ci standards.

Thank-you.

Kevin
Tucson

Brrrr, that's a mighty cold plug! According to my 1962 AC catalog its about the equivalent of Champion H-14Y which is also a pretty unpopular number. Only application I saw was 1961-62 Studebaker 6 & 8 cyl.

Maybe you will find some at Ebay.com

Gentlemen,

I purchased a set of AC 43LS spark plugs thinking they would work in my 1955 400. Frankly, it was a chance purchase without prior confirmation.

Can one of you provide me with the application details in which these plugs can be used?

Thanks

Kevin
Tucson

Well, it was a very worthwhile project, and even better the price was right and a portion of the sale went to the Packard Proving Grounds, a program that EVERYONE who has an interest in Packard cars and the company that made them should support financially.

Yup, working for me now too.