Howdy 63merc and all:
Here's an idea, why don't you try it, do some testing and see if it makes a difference for you. Start by assessing your current start up, idle quality, WOT performance and mileage. You old set of plugs will tell you alot about your engines condition and state of tune. Note the current orientation of the gap of each plug as you remove them for comparison. Plug indexing is only useful if all components of the system are in tip-top condition and tuning is optimized.
The theory is that indexing exposes the spark kernal to the incoming charge and offers an unshrouded path, for a more complete, consistent flame front and burn. Other factors that play a role in the effectiveness of indexing are quench, compression, bore diameter, plug gap and tip reach, type of plug tip
I index for several reasons; consistency from cylinder to cylinder, fastidious nature, and somewhat OCD. I buy several extra plugs at changing time, mark each and, through trial and trial, find a plug for each cylinder that has the mark in the up position. I try to keep the mark between the 10 and 2 position- That's close enough for me. I don't like the washer system of finding the correct orientation for several reasons.
I've come to these conclusions through testing. Once the optimum gap was found, initial advance set and plug heat range determined, I do a series of tests. The start and idle are very subjective, and I notice little, if any difference due to indexing. Mileage may be a slight increase. It is most evident in longer mileage tests, but conditions change more over a longer time period and it is harder to control variables. The most objective analysis is in a series of WOT timed tests from 40 mph to 60 mph. I use a stop watch and a tape recorder so I can pay attention to driving and traffic. I transcribe the tape later. Again, indexing makes a slight, but consistent, quantifiable increase in performance. A tach could be used, but practice to get consisent, reliable results in needed. For comparisons, make sure that as many variables as possible are consistent.
If you start the comparison with the plugs you've got to establish a baseline and then test with a set of new plugs, you will be comparing apples to oranges. Simply changing to new plugs will likely show improvements in all areas, whether you index or not. You might start by relocating the plugs you've got to a different cylinder for a more upright orientation, then compare.
Adding an additional 5lbs of air to all 4 tires made a more evident improvement in WOT performance and took alot less time and effort. Do not exceed the max PSI rating on the side of the tires, for very long.
I am very reluctant to report data because everyone's situation is so different. Replication is unlikely. And, I very aware of the Hawthorne Effect.
Spark plug indexing, for most street engines, is in the category of "Gnat's Eyelashes". It won't make much difference, but I know it's there. It's free and relatively easy to do.
That's my two cents, for what it's worth.
Adios, David
