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I just finished doing plugs, wires, coil and ignition controller on my 94 LT1...which is a bitch of a job. And that's coming from a guy who's done it on Porsche 911s. Imagine my surprise when I pulled the old plugs out and saw the AC logo. I know the AC-Delco merger was in 1974, but when was the last time you saw actual AC spark plugs? Maybe someone in the deep dark past had some really old stock on the shelf and decided to use them, unless there were still branded AC plugs in 1994. Seems unlikely. And given the wear on the electrodes and the huge gap (all between .065-0.080), they might have been in there since new. Or were they common in the 90s?
I found original AC plugs in my 90 when I got it. Car had 95k miles on it.
It also still had the original plug wires and distributor cap.
It was still running like this...
It may have still had the original engine oil in it as well. Seriously. I changed all the fluids and tuned it with a WB02. Now it runs smooth and strong and doesn't burn a drop of oil. Runs 13.30s in the 1/4 mile.
So apparently GM was using 20 year old stock back then. I wonder if other companies were doing the same?
I was also curious about this when I found the AC plugs in my 90. I think the plugs didn't get rebranded with Delco until 95. Which is when GM removed the hyphen between AC and Delco. There's some info on it in a thread at the Bob's the Oil Guy forum here:
Here's the pertinent post from that thread:
---------- You’re correct when GM united AC Spark Plug and Delco as AC-Delco but until the 1980-1990s GM still treated AC Spark Plug/AC Rochester Division and Delco separately. Delco was the electrical division, along with Packard Wire, and AC was filters, plugs and engine management. ACDelco without the hyphen was a rebranding in the 1990s, along with GM spinning off their parts businesses as Delphi.
I remember as a kid seeing Delco Freedom batteries in Hondas and Toyotas built in Canada or the US(especially Corollas and Tacomas built at NUMMI in Fremont, CA), and a friend of the family installing AC parts on a old Pontiac.
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Last edited by C4industries; Mar 29, 2025 at 04:41 PM.
AC plugs?
