Spark plug gap - ZR-1 Net Registry Forums

Vetman · 08-05-2021

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 · 08-05-2021

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 · 08-06-2021

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 · 08-06-2021

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 · 08-06-2021

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 · 08-06-2021

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 · 08-06-2021

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.

Sent from my SM-G950U using ZR-1 Net Registry mobile app

Mikey · 08-06-2021

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.

08-05-2021	#1
Vetman Join Date: Feb 2013 Location: Yakima Washington Posts: 401	Spark plug gap 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? __________________ Jim 1990 Z # 2441 1959 c-1 230 HP 4 speed frost blue/silver 3 owner 2011 cts-v 556 HP, manual 6 speed 1955 chev 2dr ht PP 265 3 speed w/OD

08-05-2021	#2
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,723	Re: Spark plug gap 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.

08-06-2021	#3
Vetman Join Date: Feb 2013 Location: Yakima Washington Posts: 401	Re: Spark plug gap 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! __________________ Jim 1990 Z # 2441 1959 c-1 230 HP 4 speed frost blue/silver 3 owner 2011 cts-v 556 HP, manual 6 speed 1955 chev 2dr ht PP 265 3 speed w/OD

08-06-2021	#4
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: Spark plug gap *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. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry Last edited by Paul Workman; 08-06-2021 at 07:57 AM.

08-06-2021	#5
Matt B Join Date: Jan 2021 Location: Beautiful Bavaria Posts: 523	Re: Spark plug gap 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. __________________ ZR-1 #638/1991

08-06-2021	#6
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,708	Re: Spark plug gap 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. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

08-06-2021	#7
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: Spark plug gap 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. Sent from my SM-G950U using ZR-1 Net Registry mobile app

08-06-2021	#8
Mikey Join Date: Jul 2020 Location: Nashville TN Posts: 323	Re: Spark plug gap 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.