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If you are looking to squeeze just about every last ounce of horsepower out of your engine and you are getting down to taking out your passenger seat and stereo just to gain a half horsepower, then perhaps it is time that you seriously look at indexing to add a few newfound ponies.

This is actually one of the oldest tricks in the book, other than the famous pick-up line, “You must be tired… because you’ve been running through my head all night.” But unlike some of those tired old pickup lines, this trick actually works!

We mentioned spark plug indexing in Part 3 of our series, but we didn’t really have enough room to tell you how to do it. We highly recommend the purchase of spark plug washers, which will enable you to index any plug.

If you don’t use washers, you are going to have to buy a stock pile of spark plugs to find the perfect matches for your engine. And it always seems that out of eight plugs, you won’t find more than two or three that will work reasonably.

You can find index washers at just about any performance shop and they should look something like these, featured on the Summit Racing website. There should be three thicknesses that will get you to the angle you need, depending on how far you are off in the first place. Which brings us to the steps of the process.

Step 1:

Take the plug you intend to use for the cylinder and using a magic marker, mark a line down the white portion of the body where the ground electrode attaches to the body of the spark plug.

Never use pencil for the marking as it can cause carbon tracking and thus poor spark plug performance.

Step 2:

Using a diagram of your engine, either found in a mechanics book or on the Internet, find where your cylinder is in reference to where your spark plug is going, and in particular take notice where the exhaust valve is facing.

Indexing works in theory because the open gap of the plug is being place in the direct path of the rushing fuel/air mixture, which gives it a much better chance of igniting the mixture completely, than if the ground electrode is in the way.

The reason you want to angle it towards the exhaust valve in most engines is that the force of the mixture is usually moving towards the exhaust valve inside the cylinder. Of course, every engine is very unique, so you may want to experiment a little to see what exact angle achieves the best results.

Note: The only problem with such experimentation, is that without a professional engine dyno… using the “seat of your pants” dyno you will be hard pressed to feel the difference of a couple horsepower… but you can sure try!

Step 3:

Once you know where you want your gap to be facing, go ahead and twist the plug gently into the cylinder wall until it is snug and see which way your line is facing as compared to where you need it.

Remember that you will need to turn the plug approximately a quarter turn or so to tighten, so keep that in mind during your estimation measurements.

If you are close enough, tighten the plug up and move on to the next one. If not, then look at the distance you need to turn the plug in order to be in the proper location and decide between the three thicknesses of washer which one will work best to get you within range.

Note: Never double up on index washers. You will lose compression in your engine. You should be able to reach any destination you need with one of the washer sizes.

Step 4:

One you are within range of your goal, go ahead and tighten the plug and move on the the next plug.

While this does not always guarantee you results of improved engine horsepower and efficiency, it has been proven time and again to work, so the odds are actually more in your favor than using any of the “trick” spark plug designs.

Yes, sometimes the best tricks are the oldest tricks (and least expensive to boot)!