Yep, backside is correct.

I had forgotten when working with Rossiz on his Z..... we looked it up.

yup - easy to mix that one up.

and you can bet i'll have a rag handy to protect from things going over the "cliff of doom" next time i open the valve cover - too scary!!

well, after a week of driving i checked the plugs and i'm happy to report a great improvement.

plugs before seals were replaced: lots of oil around the perimeter, and the threads would literally be wet w/oil when i took plugs out

after seals replaced: looking good. i still seem to have a little bit of unhappiness on #3 and #4, but definitely an improvement. the odd thing is that those two clinders also seem to run rich - i'm thinking i've got unbalanced injectors, probably time to change them out...

About 20 years ago, I sent my injectors into Marren Motorsports for cleaning and they told me they were beyond saving. They found me new Ram brand injectors and when they flow tested them, they were all over the map, so they ordered something like 18 more injectors and flow tested them all to finally get a matched set within spec. They were shocked at how much variation they were seeing with the new injectors. The bottom line is that injectors new or old can and will have very different flow rates.

I've heard that reading plugs isn't what it used to be. From what I gather, it's OK for plugs to look leaner than they used to in the past. Ten years ago, the white insulators on 1,2,5, and 6 would be called lean. Some people have cited gas formulation changes that have "shifted" the norm?

My highlander for example, the plugs come out looking scary lean, but everyone tells me they look perfect. Scary lean...

BTW - Did you know you're running the "wrong" plugs for your year?

http://www.classiczcars.com/forums/electrical-s30/47495-spark-plugs-projected-tips-vs-standard.html

@Jeff: understood - on my bikes (ducati twins) i've always had injectors matched and it makes a noticeable difference when tuning for afr - the shop keeps about a half dozen new injectors on hand and when they order a new set they flow test to find a matching pair. too bad you can't adjust them...

@Cap'n: yes, i did a bit of research on plugs and the projected tops seem to run fine so i'm happy with them.

Did your research turn up any info as to why Nissan moved away from the projected tips from 75 to 79 only to go back to them in 80? Any ideas? I've continued to wonder.

P79/90 head vs N42/47

P79 came in '81 though, so if they reverted in '80, it would still be the N47 head.

It's not a big deal or anything. I'm just curious. I've had both projected and non-projected styles in my 77 and didn't notice any difference. It could be anything from slightly better emissions test numbers during those years to a typo in the manual.

Denso/NGK price brakes to Nissan?

CO, for experimental fun, I would try to pick a day where you can advance the distributor to just get the projected plugs to ping going up a hill... then swap in the regular plugs and see if the ping stops...this may prove the flame front theory.