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Opinions on which AC spark plug to use

Started by papas52cad, April 10, 2019, 08:06:47 AM

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papas52cad

Looking for guidance on which spark plug I should use as I prepare to change them in my 52 caddy with the 1960 390 motor. This car now has the newly carter AFB done at Daytona parts installed, so I thought I would take the next step for any improvements new spark plugs will offer.
The last change was 3 years, 10,000 miles ago, with AC R43S plugs. Another caddy owner with 390 experience in his caddy’s uses AC R45s ( hotter plugs according to google).
I will appreciate thoughts from the forum on what is best.
Thank you.
Peter
1952 Fleetwood

hornetball

Personally, I would stick with the OEM recommendation.  What do the firing ends of your current plugs look like?  Can you post a pic?  It it ain't broke . . . .

papas52cad

Thank you
I’ll pull a few this morn8ng and get photos over..
Last I looked they weren’t bad, but that is subject to interpretation by more experienced folks..
Stay tuned
1952 Fleetwood

Cape Cod Fleetwood

Quote from: hornetball on April 10, 2019, 08:10:22 AM
Personally, I would stick with the OEM recommendation.

There are 2 kinds of cars in the world, Cadillac and everything else....

The Present -1970 Fleetwood Brougham

The Past -
1996 Deville Concours
1987 Sedan De Ville "Commonwealth Edition"
1981 Coupe De Ville (8-6-4)
1976 Sedan De Ville
1975 Sedan De Ville

The Daily Driver and work slave -
2008 GMC Acadia SLT *options/all

Roger Zimmermann

If I'm right, the recommended spark plugs were 44 or R44. No more available, unless you find some on eBay.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

papas52cad

Hello
Yes I think 44 was correct but none were available when they replaced Lin 2016
Here is what the 6 easiest to get at look like, let me know based on these if I leave or change, also from other posts I understand gap to be 0.40..correct?
The driver side were at 40, but the 2 passenger were less, more like 30-35, so I will correct to 40, if that is preferred
Pls let me know how I should proceed.
Thanks for your help
Peter
1952 Fleetwood

Daryl Chesterman

#6
Those spark plugs look good.  The one on the right in the picture below (third picture down that you posted), looks like that cylinder is running a little rich.  The only reason to go to a hotter plug would be if you had an engine burning oil, and fouling the plugs.  Yours look like there is no oil burning problem.  Factory gap is .035, and I see no reason to deviate from that unless you have installed electronic ignition, and someone more knowledgeable than I would have to weigh in on whether that would require changing the plug gap.  If those were my spark plugs, I would re-gap them and put them back in for another 10,000 miles.

http://forums.cadillaclasalleclub.org/index.php?action=dlattach;topic=155039.0;attach=133768;image

Daryl Chesterman

papas52cad

Thx Daryl
I cleaned them all as suggested And set gap at 0.40 as my car has the Petronix ignition installed and I saw a post from a year or so ago where Art Gardner recommended this set up.
All are back in the car and it is now running as good as it ever has!
I’ll save the $20 for gas!!
Regards
Peter
1952 Fleetwood