I picked up a set of AC-Delco 41-974's awhile ago and when I checked the AC-Delco website there is no reference to them. Evidently, they have been superceded. They're supposed to fit my C5 2K Vert, but I have no info as to the type, heat range, or gap setting. Can anybody help out?

 

Never heard of those plugs. The stock plugs (41-952)on my 2000 were crap. Half of the platinum inserts were gone in 10K miles. Better off with a set of iridiums like the NGK TR55IX.

 

Chebby bulletin, 03-06-04-060, updates spark plug application and gap.
As of 24 October 2003, part number 12571164 is the replacement spark plug for ALL c5 Corvette, LS1 and LS6.It also shows a new gap, of .040, is set at the factory. Don't attempt to regap this plug as it could damage the plug. Do NOT USE THE PLUG, if the gap of .040 is not there.The new plug has an Iridium tip for the electrodes.

The ACDelco number is 41-985.

 

agree apply a touch of anti-seize and torque to 11#

 

ttt

 

I've been looking for plugs myself. I've looked at NGK, Denso and Delco. Take a look at this thread I initiated. http://forums.corvetteforum.com/showthread.php?t=990985
It's amazing, but no one seems to know why their plugs are gapped the way they are, and why different gapping recommendations exist, for the same pregapped plugs, on different year Corvettes. At least Delco calls for the same iridium plug, with the same gapping on all 1997-2004 C5 Corvettes (LS1 and LS6 engines). I was planning to put in NGK TR55IX plugs until I saw odd gapping recommendations, that didn't seem to follow other iridium plugs, and no one could explain the whys and wherefores to me. I'm now leanng to just buy the Delco 41-985 iridiums and be done with it. All that bothers me is the problems that seem to follow some Delco parts (i.e. platinum puck plugs, leaking battery posts, batteries just failing, etc., etc.) I wonder who makes the Delco iridium plugs for them?
Ed

 

I had 41-974's in my '03 Z06 from the factory. They are the old platinum plug that was specified before the 41-985 Iridium plug.

Info I found on the web pertaining to gap:
"From page O-41 of my 2001 Service Manual 1.524mm (0.060 in) Gap" I would assume this is the recommendation for the 41-974 and not the Iridium 41-985.

I read somewhere that the 41-985's are made by Denso. When I installed mine some had been handled 'roughly' and the gaps weren't consistant so I kept the factory recommendation and gapped all to .040. It does idle and run smoother than the 41-974's that were in there.

Some info I found on the web on Iridium:

"Iridium is a precious metal that is 6 times harder and 8 times stronger than platinum, it has a 1,200=F higher melting point than platinum and conducts electricity better. This makes it possible to create the finest wire center electrode ever. Prior till now, spark plug manufacturers have favored platinum for their long life or performance spark plugs due to its high melting point, also the technology did not exist to machine and bond iridium on a spark plug electrode(at least in a cost effective manner). Champion spark plugs had already made an iridium industrial application spark plug, but it still sells for over a hundred dollars per plug. Just now is the technology available to effectively use iridium in a spark plug for automotive applications. The strength, hardness and high melting point of iridium make it very well suited for a fine wire plug. The primary iridium plug manufacturers at this time are Denso with a 0.4mm center electrode and NGK with a 0.7mm center electrode. Both are the best performance plugs on the market for traditional automotive use and many racing applications."

 

I heard the same. The Chebby bulletin, 03-06-04-060 is pretty adamant about not trying to regap 41-985s that are "off." I guess the days of smacking an electrode on the corner of a work bench to change the gap are over. At 30K I switched from the original plugs on my '00FRC to NGK TR55s. The engine was not happy, idled weird and surged. I know alot of LS1 folks run the NGKs and love 'em and I believe that they're experiences are true. However NoGo at East Side Dyno told me he wouldn't use NGKs and showed me a nasty bunch of fouled, cruddy plugs. When I switched to the 41-985s, everything returned to fine.

Regards,
Garibaldi

 

I don't agree with not fixing an incorrect gap. I use a gapping tool, not the traditional garage mechanic 'smack it on the bench method', and haven't had any issues. What does the GM bulletin suggest for Iridium plugs with an incorrect gap?

I read somewhere that the ignition system is not designed for spark plugs with traditional copper electrodes. As I can remember, it takes more energy to fire the larger electrode plugs than the platinum or Iridium. The increased energy required to fire the plug results in a less powerful spark that could lead to early fouling.

 

Hey Guys, thanks for all the info, I owe you all. This Forum is the greatest. Where else can you get such in depth answers.