Spark Plug Gap

I just bought a set of AC iridium spark plugs #41-985 for my '99 5.3. On the box it says set gap to vehicle specs, which happens to be .060". However, on the AC Delco web site for these plugs it states, "DO NOT DEVIATE FROM PRESET GAP .040". Anyone know which is correct?

Because they are iridium I would leave them alone. The factory replacement 41-952 superceded 41-932 is gapped at .060 I would believe the website, personally. -Chris

Your spark plugs are supposed to be gapped to .060" like your vehicles recommendations

Your spark plugs are supposed to be gapped to .060" like your vehicles recommendations
What if the reccomendations have changed since then? Auto manufacturers are constantly upgrading their parts, and probably found the newer gap to work better. I would call the dealership parts or service department and ask as they are supposed to have all the up to date information.

Leave them at .40 I changed the plugs in my 2000 silverado and got the older stock double platnium plugs gapped @ .60 and ran into tons of problems with carbon arcing across the porcelin of the plug because the resistance was too high with new plugs and older wires (only 80,000 km's). The gm tech told me that the .60 gap makes a hotter spark and helps with mileage a bit but makes for harder starts in the cold. He also said that he NEVER gaps plugs @ .60 EVER. I replaced my plugs with the iririum plugs and left the gap at .40 as well as replacing the wires. It has been hard to tell if there has been a drop in mileage because of the gap change because of it being so damn cold here (-25c to -35c) but it does not seem to run any different.