Spark Plugs

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This was posted under the Buick Pre War heading.  Perhaps someone here can help this fellow.

Hi from Athens, Hellas

Here in my country (Hellas, South Europe), I'm proud to be the sole Franklin (straight 6) 11-B (1927) owner.

It was my late father's favorite vehicle among 27 Historical Vehicles of our private Collection.

My Franklin has now W14 on it, but fellow Franklin owners from U.S suggest W18.

My technical knowledge on Franklin so far led me to fit W14 on again, as they have caused no trouble for the last 25 years.

But W18 still remain a vivid suggestion choice by American fellow Franklin owners, whom I always pay great attention to.

Can you please advise which type should I finally order? The colder W14 (now installed on my Franklin) or the hotter W18 (suggested to me by fellow owners)? I can only point out difference to reach factor (0,75" vs 0,625"), but they reassured me that I will have no problem switching W14 to W18 - they will fit like a glove on my Franklin's head.

Please, if it is convenient for you,  send me your suggestion based on your vast personal experience.

Yours

K.L.Zekakos, Dipl. Mechanical Engineer.