Tag Archive 'spark plugs'

Jul 10 2008

DIY Spark Plug Indexing

Doing a tune up? Replacing spark plugs? Just wanting to check things out? While you’re at it consider indexing your spark plugs. This is one of the few ignition modifications that can make a very small difference in engine performance. As said by the folks at Advance Auto Parts: “Real-world power gains vary. Some engines or combinations respond differently than others. In fact, all engines will pick up power, but some gains will be more dramatic than others.In the end, it can’t hurt to index the spark plugs. This can contribute to superior engine efficiency and improved economy.” So, no promises, but it can’t hurt!

Purpose: Indexing the plugs allows the flame to spread more uniformly through the combustion chambers in the individual cylinders. I am certainly not about to claim a plethora of scientific knowledge on the subject but I’ve seen many dyno charts supporting the theory and have thus accepted the idea that it’ll help. It’s really not too much extra effort on top of replacing the plugs, so what the heck.

Time: 20 minutes

- Socket Wrench
- Spark Plug Socket
- Extension


1. Go to the parts store and buy yourself some new spark plugs, preferably Denso U-Grooves or NGK V-Powers (basically the same). They’re the recommended stock replacement and generally used plugs; cheap and effective. Again, I do not profess to be a spark plug wizard.
2. Pop them out and take a look at how they get their name.

3. Mark with a marker the on the white part where the opening on the plug is. This will allow you to see where the opening it when the plug is in the head getting adjusted.

5. Go out to the car, yank your plug wires and then your old plugs.

6. Stick a new plug in and tighten it down and see where the opening is. On most cars you’ll want the opening facing the exhaust, but it’s different for everybody.
7. If it lines up perfectly stock, you’re lucky, if not, grab a copper indexing washer and throw it on the bottom of the plug and see how it works. There are different sizes of washers and all that to try and get the indexing right, so just mess around until you get it.

See if you can see how it’s lined up:

8. Once they are all indexed, slap everything together and be happy.

There are two methods of indexing, one is to buy lots of plugs and attempt to get lucky, the other is to use washers, take your pick. I chose to use washers rather than to try my luck. Less wasted gas driving to the store.

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