AC 41-985 11571164 spark plugs once again 1999 LS1 Camaro

[wildrq]

Ok, here I go again. recently bought a 1999 Camaro with the police B4C package and it has a LS1 engine. It has 127k and I took out the original AC plugs, part number right on them, 41-985 and 12571164. THEY WERE GAPPED AT .060 from GM!, not .040! ALL OF THEM.
Since GM says to use the new 41-110 plugs and you cannot find the old 41-985 ones anywhere, if you use the new AC plugs and keep the gap at .040, you will get less miles per gallon and sometimes have backfires on deceleration when you get on it. TOO MANY PEOPLE HAVE COMPLAINED ABOUT LESS MPG AFTER PUTTING THESE 41-110 PLUGS IN! Then they go off and look for something else that caused it. When all they changed was the plugs. Doesn't THAT tell you something?
The old 41-985 plugs are COLDER plugs, I'VE COMPARED THEM SIDE BY SIDE TO 41-110s AND THEY HAVE A DIFFERENT ELECTRODE LENGTH, LONGER INSULATOR - THEY ARE A COLDER PLUG!
Just want to through my 2 cents in, because this is the TRUTH. GM should NEVER have quit making the REAL 41-985 plugs. AND THEY WERE NOT PLATINUM PLUGS. THEY WERE IRIDIUM.

I'm STILL looking for an acceptable replacement and believe I have my work cut out for me. I have measured the thread length, electrode length, insulator length, etc. and have not found ANY brand of plug to be the same as the 41-985s. I even tried a set of platinum NGKs because they were the closest length, etc., and the car did NOT run right. Misses, etc. The old AC 41-985s are back in it and will stay in it until I figure out what works at least SOMEWHAT close to originals.
Comments appreciated, but please don't dispute or dismiss me, this is EXACTLY what I have found out.
One last thing, the B4C option was only available with a 3.23 rear in 1999 and a cold plug is exactly what I would want with a car that will do 163 MPH directly from GM, no mods. Thanks for taking away what worked GM.
- An old Chevy guy.

[cammed goat]

Look into the Delco R44-LTSM plugs. They are iridium and may have superceded the old 41-985 plugs. I believe the R44s came in the 04 GTOs. Not sure what other cars they came in. Let me know what you find.

[wildrq]

The R44 LTSM are copper plugs. They might work, but I'd like to use Iridium plugs because of the longer life. It's a PITA to replace these, especially the right side and back right one. Thanks anyway, but I'm still looking. One person posted on another site the Denso are better than NGK - that is not the way it used to be, Nippon Denso or ND plugs were called "No Dice" by parts people that knew- and he recommended Denso IT16 and a colder plug than that was Densco IT20, I will look at these if I can find them local, but still would prefer an AC Delco plug if I knew which one worked the best. I used to use NGKs in Jap bikes and they were great, but the platinum NGK ones I used in this Camaro did not work well. Maybe their Iridiums work, I don't really know.

[SMWS6TA]

I ran the KGK Iridium's for about 18 months till I started modding my car. They ran good and gave me good gas mpg and no negatives in HP.

[wildrq]

Ok, I'll give them a try. Do you know what number NKG - TR55IX (7164?) or TR5IX (7397?) and are both Iridium plugs? -and what did you have them gapped at? Thanks.

[35th-ANV-SS]

The TR5's and TR55's are the same exact plug aside from coming gapped differently. Both have the same heat range. Based on the latest recommended gap from GM for the LS1, the TR5 would be the better choice. Scott can confirm.

[35th-ANV-SS]

Oh, and the gaps are 0.040" and 0.060"; TR5 being the lesser of the two.

[SMWS6TA]

The TR5's and TR55's are the same exact plug aside from coming gapped differently. Both have the same heat range. Based on the latest recommended gap from GM for the LS1, the TR5 would be the better choice. Scott can confirm.

correct. I used the TR5IX's. Even though they say you can get 100k miles out of them I would still check them every 25k miles. I swapped back to the TR5's because once I started modding the iridium's just didn't last as long and if I had to swap plugs every 30k miles the copper core TR5's seem to last for that duration and are much cheaper in the long run comparing to iridium.