AC Delco Spark Plugs

Are replacement spark plugs even necessary?

No, as long as you are not having any problems. But, if you have installed UltraPower and are looking for that last ounce of performance then yes they are worth the cost.

If you are going to try to justify the cost of Taylor wires and/or AC Delco plugs on increased HP/TQ and/or gas mileage then you are going to be very disappointed. The HP/TQ will only show up on a dynamometer as the "Butt Dyno" does not have very accurate gage. As for the mileage increase, if any, it would be in the .1 or .2 mpg under the very best conditions.

Some 8.1L engines come with Denso brand spark plugs installed. But, most come with AC Delco 41-983's gapped at .060. If you install UltraPower you have 2 choices in spark plug upgrade.


  1. Regap the stock 41-983's to .045 and reinstall.
  2. Install 41-101's or 41-993's gapped at .045.


  • If you have Denso plugs installed you may want to consider a new set of AC Delco's.
  • The 41-101 Iridium replaces the 41-993 Platinum which replaced the 41-932.
  • There is a How To R & R Your Plugs in the Tech Tips section.

What is the difference in plugs?

The 41-101/41-993 is a hotter plug and better suited for the 8.1L with UltraPower installed.

Why replace them?

Here is a set of Denso plugs with 78,000 miles on them.

The 2 photo's show the difference in the combustion flame travel, the platinum tips are almost gone  and the gap is more than the .60. The next photo shows the difference between new and old.

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