I have been reading 2 hours on plugs etc. I see where the factory is .60. Also I see this info below in anothe rpost and it says dont' regap .40 41985 plugs

I want to use the irdiums since they last a long time. I was thinking of using a gap of .50 to .52 Ihave a cam and bolt ons.

But can I regap the irdiums and not hurt the time. And indexing the plug seems like a pain.




2002-2004 GMC Sierra Denali

2003-2004 GMC Envoy XL

1998-2002 Pontiac Firebird

2004 Pontiac GTO

2003-2004 Hummer H2

with 4.8L, 5.3L, 5.7L or 6.0L V-8 Engine (VINs V, P, T, Z, G, S, N, U -- RPOs LR4, LM4, LM7, L59, LS1, LS6, LQ9, LQ4)

A new spark plug has been released for use in the above vehicles. The new spark plug has an Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the spark plug has also changed. The new spark plug, P/N 12571164 with AC Delco P/N 41-985, is gapped to 1.01mm (0.040 inches) when the spark plug is made. The spark plug gap is set during manufacturing and should not be changed or damage to the spark plug may result. Any new spark plug found to not be properly gapped should not be used.

Document ID# 1396703

 

Go with copper and set the gap to factory specs.

 

That wasn't the question lol.

Yea copper is good (I think I got some in there now), but I want to get some plugs thats good for 50k miles. Not10-30k.

so back to the question gap on these NGK/AC delcos

Thanks guys

 

This is correct...

Use those and verify the gap. You shouldn't have to change 'em though.

 

If they built them for your app. at .040 then why gap them. Factory gap is for factory style/type plugs. Just put them in and report back in 50,000 miles.
I run copper plugs at .050".

 

I guess I might.

Factory stock plugs plats are .60. I know this is different material but .40 seems low even. the nos tr6's they use most people do .35 to .38 with NOS.

 

The new gap is because they're iridiums instead of platinum. They issued the tech. service bulletin for a reason. The new .040 gap and new iridium plug is correct. Check the gap before install. Better yet, bring your gap checker to the store (or buy one at the store) and check them before you go home. If the gap is wrong, don't buy that plug.

Those NGK's that you mention are not iridiums...they're copper. You can't compare a N2O application plug to a factory replacement plug. There's different theories at work due to higher/hotter cylinder pressure/temperature conditions.

 

Thanks that confirms what I was thinking!

 

Is a .045 gap ok for a stock application? (TR55 plugs)

 

It's OK but .050-.055 makes for a little better flame.

 

IIRC, TR55's are gapped at .055 from NGK.

 

^they are.....my car is running so good right now with the NGKs (gapped @ .045) v. the ac delco platinums. I wonder if a .055 gap would help things.

 

Use .50. .45 is too low IMHO.

 

Since stock is .060 and the TR55s are already at .055, I'll replace them without touching the gap and see how that works........It's amazing how a plug that costs $1.79 soooooooo outperforms a $7.99 plug........

 

It's the difference between a 30k mile copper plug and a 100k mile platinum/iridium plug. TR55's perform better at the expense of plug life. If you were looking at warranty claims (from GM's perspective) and you saw that the time required for a plug change on an f-body takes 2 hours, it doesn't make too much sense to put in something that'll last only 30k miles does it?