Spark plug gap

[Vetman]

I have a stock 90 z with Marc?s chip. I?m putting new plugs in. My lt-5 engine manual says gap at 50. Others here have mentioned gap to 35. What is best?

[secondchance]

I believe, if running copper tip, .035. If, platinum tip, .050. Iridium, I think, is .045 - not positive. It?s been a while...
Best would be to follow plug manufacturer?s recommendation. Spark plug technology marched on since manuals for our Z were written.

[Vetman]

Platinum. AC Delco 41-801 is what the Chevy dealer said the 1990 LT-5 called for. Hope this is right. I?m driving 3100 miles to Carlisle in two weeks!

[Paul Workman]

Pete Polatsidis put me onto AC Delco COPPER plugs (41-602) gapped at .042". They sparked his stock block LT5 to 11.xx sec quarter mile runs @ close to 129 mph in 3rd gear!

The copper plugs are cheap enough that you can replace them annually w/o breaking the bank (about $2.50 last time I bought mine) - less than a tank full of 93 octane.

Plug wear is insidious enough that you don't really notice the degrading performance in normal driving until it becomes bad enough to cause misfires under load - somewhere above 10,000 miles for a copper plug, 50k+ for rare earth plugs. I seldom go more than 3k miles B4 putting in new plugs. That way I never have to think about plugs - especially when optimizing the tune.

Justa thought.

[Matt B]

I'm running Bosch 9607 Fine Wire Double Iridium, these are gapped at 0.44 (1.1mm) and seem to work very well. During my research I read the simple copper plugs are gapped tighter to achieve a longer lifetime as continuous wear increases the gap over time.
But the tight gap is supposed to have some disadvantages, so copper plus improve over time to reach their optimum capabilities before "fading out".
Using rare earth plugs allows less wear so the gap can be chosen more optimal without losing lifespan due to wear.

So, long story short, the wider gap of (double) iridium or platinum plugs is because the wear slower than copper. That's what the internet said . Leave it to the pros here to confirm or reject my words.

[XfireZ51]

Like Paul and Pete, I use copper plugs since u can buy a full set for $20+. I just installed the NGK BKR5E-11 which are gapped .044? out of the box.

[jss06c6]

Concur with Pete, Paul and Dominic. I'm running NGK 4177's (TR6) in my 91 as well as my client's LT-5's. Gapped at .045". I put these same plugs in the LT-1 as well as the LT-4... however I use a .037" gap in those engines...

Fyi, my experience with iridium plugs (NGK) is that the wasted spark system wears them out (electrode tip erosion) very quickly. Expensive plugs to replace that frequently.

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[Mikey]

Copper is a far better conductor than platinum or iridium. Exotic metals only became a thing when people became too lazy to change spark plugs more often than 100,000 miles. I had issues with the platinum tips blowing off my 383ci LT1 1994 and switched to copper as Pete recommends also. I change them at 10,000 miles. Car runs phenomenal.
I will do the same for my LT5 soon.