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Discussion Starter #1 (Edited)
I bought new plugs for my 04 Z06, and was told that the stock gap was .060. However all plugs pulled thus far have been .039. The gap on the new plugs was also supposed to be .060 as they are the NGK TR55-IX. The gap on these out of the box was consistently .058.
1. What if any do you guys think this change is going to do to the performance of my car?
2. Why was my stock gap so far off from what I was told?
3. Has anyone else had a similar experience with their stock gap measurements?
4. I wonder if this is a difference for 04?

Any thoughts?
 

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Bulletin No.: 03-06-04-060

Date: October 24, 2003

INFORMATION
Subject: Information on New Spark Plugs and Gapping

Models:
2004 Buick Ranier
2002-2004 Cadillac Escalade, Escalade EXT
2003-2004 Cadillac Escalade ESV 2004 Cadillac CTS-V
1997-2004 Chevrolet Corvette
1998-2002 Chevrolet Camaro
1999-2004 Chevrolet Silverado
2000-2004 Chevrolet Suburban, Tahoe
2002-2004 Chevrolet Avalanche
2003-2004 Chevrolet Express, TrailBlazer
1999-2004 CMC Sierra
2000-2004 CMC Yukon, Yukon XL
2001-2004 CMC Yukon Denali, Yukon XL Denali
2002-2004 CMC Sierra Denali
2003-2004 CMC 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, LSI, 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 1.01 mm (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.
 

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Iridium plugs come gapped from the factory and are not supposed to be regapped. This is what it says on the Denso website. If you try to regap, you damage a coating put on the tip. Be careful not to scratch the plug's tip when measuring gap.
 

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Go with speedratchet. I read the same bulletin yesterday. I was going to go with a stock plug, and this is what I was given for a part number. :z:
 
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