NGK vs. AC Delco spark plugs

[70 Forest Green Zee]

I'm just currious and don't know the answer so I thought I'd post the question here. I've always used AC Delco plugs in my 70 Z28 with the stock LT1 engine. I've heard so much good about NGK plugs that I decided to try a set. My question is this....the electrode on the NGK is substantually longer than the AC Delco plug....will this cause any problems? The pictures below are an AC Delco R43, and an NGK XR5 V Power both of which are the correct plug for my application. Your knowledge is greatly appriciated!

[John Brown]

The XR5 looks more like a R43S than a R43. On a Z28 the tip of the plug might touch the piston, if you still have domed pistons. You might want to see if you can cross reference the R43 plug and see if it crosses to something other than the extended tip XR5. Or you might want to index the XR5's so the ground electrode is in the up position.

[Salvatore]

I run R44S in my 69 Z and have no problems. You will know if they hit. The electrode will be closed. Is there an NGK chart I can use to cross reference AC Delco plugs to? Thanks, Sam

[Mr. Chevy]

I think you will be fine. What I would do if you really want to be sure is put one in, disconnect the main coil wire so the car won't start and crank the engine over once. Pull the NGK plug out and check the electrode. If it does hit it shouldn't damage the piston like it would if you fired it up and ran it at a much greater rpm at idle..

I did this with my car just for my own peace of mind when I switched to the NGKs. They are great plugs and you will notice a world of difference..

Rich

[Mr70]

Sam,does THIS help?

[JimL78]

I always ran AC 43N sparkplugs in my L78. I couldn't find them when I went to get my car last year so I put the equivalent Autolights in it. Thought that was sacrilegious putting Ford plugs in a Chevrolet. Over the winter I found some NGK plugs that look identical to the 43N. They are B7ES. The heat range seven doesn't have the projected tip like the fives do. Maybe you could use the seven heat range in the shorter plug and it will match up to the old ACs.
Jim

[YENKO DEUCE REGISTRY]

My XR5's don't hit the pistons, and they work great!!

[Salvatore]

Do you run the XR5'S on the street or a heat range higher? I use R44S what would the NGK number be to that? Thanks!

[70 Forest Green Zee]

Sam...I think the next heat range up is the XR4 for NGK. They are just the opposite of AC Delco...Delco the higher the number, the hotter the plug...NGK the lower the number. the hotter the plug.

[RamAirDave]

Month+ old thread, I know....

My 70Z is a ~58K mile, original-build engine. Ran great for the last ten years with R45S, then switched over to 43s about a year ago. It doesnt care for those too much.

Thinking of putting some XR5s in it based on all the good reports, along with a new set of points which are probably 10 years old. Think the XR5s would be the correct plug, or should I step up/down a heat range considering it's never been rebuilt?

It'll still 4-wheel slide , but isnt quite right at WOT