What is the correct OEM restoration spark plug for a 1970 442 455? I'm going to give the Pace Car a tune-up and might as well buy the right ones the first time around. I have some old NOS plugs lying around in a box, so I might have the right ones already.

 

AC R44S would be my guess. My 70 Toronado used AC R45S

 

Have you looked at the underhood (emissions ) decal ?
On some models the recommended spark plug numbers are on it.

 

think its R44s?

 

If you have NOS AC Delcos that are at least 15-20 years or older you're probably OK.
AC Delco is no longer made in the USA and hasn't been for a while. Current ACs are not the same quality they once were. The same goes for Autolite, Champion et al...

I did some homework last year. I needed to replace the 20-year-old Autolites I swore by since 1975. Autolite has been offshore for a while and is pure junk according to my research. One theme kept popping up...quality control(on all specifications and all offshore brands). It's hit and miss on all brands, and longevity is a fraction of what it was 25-50 years ago...shocker there huh? Literally, within a few hundred to a few thousand miles plug failure was reported. Some bad out of the box some actually fell apart in service. Not what I want in my engines.

We no longer have the convenience of walking up to the counter and asking for plugs points cond rotor cap n wires and expect to get decent quality, Jobber quality was the garbage back in the day. Now the "good" stuff is below jobber junk. You have to shop smart and most of the time pay a premium for good aftermarket parts made in the USA.

Currently, NGK V-Power XR5 research as "good". Good quality and made here if you can believe it. I'm running a set now so the jury is still out. Ill pull them after 500 then at 1K to see how they are doing with the HEI.

You can see from the progression of this 10-year-old thread where things are now.

https://classicoldsmobile.com/forums...s-39090/page2/

 

Buyers must be careful where they buy their plugs from also. Counterfeits are common when buying thru Amazon

 

According to GM parts information, R44S is for 70 4400 455 4bc. GM p/n 5612072.

People that have the old OG green rings think they're made of gold, though. Shop accordingly.

 

I have been running ACDelco 45S in my 455 with E heads and 15cc cast pistons for about 5,000 miles. I pulled a couple of them to take a reading and they seemed fine to me. I am no expert at reading plugs, but aside from the light covering of milk chocolate brown deposits on the ground strap and porcelain, the plugs almost looked brand new.