Indexing Spark Plugs

[frankeeski]

Entering the final stretch for my new engine build. I am buying a few parts each week, I'm down to spark plugs, a wire set and a MAF calibration. It came to me that something I take for granted, may be something some or many of you don't know about. I learned very young about indexing spark plugs. Some say you can gain 1 or 2 horsepower depending on your setup but I do it more for a clean fuel burn and efficiency. I basically buy two extra plugs each time, meaning if you have an 8 cylinder you buy 10 plugs. You want to set the strap of the plug to orient it towards to exhaust valve. This sets the open area of the plug towards the intake valve. There are videos on youtube with great explanations on how to do this with and without indexing washers so check it out.
http://youtu.be/Ys4GnIk_YC0

[David Hodgkins]

Wow, never knew about that. Thanks Frank!

:)

[68GT500MAN]

I am with David on this one, learn something new every day (or is it remembering something I learned many years ago?). Thanks Frank!
Doug

[BillJackson]

Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.

However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.

In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.