69 z sparkplugs

[Steve Shauger]

I run NGK's, and seem to never foul. Based on the responses I may switch to Autolites next time.

[Mr70]

There is,I went from Autolites to NGK.
I'm staying with NGK.

[x33rs]

Yes Steve, NGK's are good. Japanese made I believe. We run them in my fathers 760hp Pontiac. Just have to keep in mind the NGK heat ranges work backwards, meaning the higher number is the colder plug.

[jdv69z]

What's NKG's equivalent to AC 45?

[x33rs]

XR4, that's as hot as they get.

That's equivalent or close to the R45S AC plug which is an extended reach plug (electrode and ground strap extend into the chamber slightly more) which is better for flame travel.

I don't believe NGK makes the shallow plug that would be equivalent to an AC R45 (no S in the part number) We always called those oil burning plugs because the electrode and ground strap were very shallow and not out in the path of the chamber.

I ran the XR4's in my Z for about 2,000 miles as an experiment. Worked fine up here at 5,000 ft. But had #2 and #3 showing a tad rich, which runs off the left front corner of the carb. I wanted to go to a warmer plug but NGK doesn't make one hotter. So I tend to believe the XR4's may be closer to the R44S heat ranges because those plugs worked similar. I already had the carb stagger jetted for best power so I decided to switch to Autolite 86's, which are as hot as they go and equivalent to R45S. Been clean ever since.

[Mr70]

My L-78 Chevelle takes AC R43T from the factory.
The NGK equivalent is stock #2771 UR5.

[x33rs]

Is that a mistype??

The "T" in the AC line means that's a small 5/8 taper seat plug. The "U" in NGK line is also the small 5/8 taper seat plug.

I wouldn't think that's a typo twice??

I ask because shouldn't L78's be a square port large gasketed 13/16 plug head?? Or did GM go to the small plug on L78's in 1970??

[Mr70]

Sorry about the confusion,the T is correct.
And yes,because it's for my 1970 L-78 Chevelle.1970 LS-6 & LS-5 used same.
I know this is about a '69 Z/28 camaro,just wanted to add my usage for posterity.

[x33rs]

Cool, learned something new. I always thought the big plugs were used up through 1970.

All my BBC stuff is 71-72 that uses the small plug. I figured the change was 1971.

[70 Forest Green Zee]

The T stands for taper....the spark plug itself is tapered to match the taper of the spark plug hole in the head where the plug screws in and there for does not use a crush ring to seal tight to the head like an R43 or R44 does.