Sparkplug modifications "indexing" etc.

[Guest Anonymous]

Discovered a pile of different sized copper sparkplug gaskets/washers. Was wondering if anyone on this board is serious enough to actually index their plugs and whether they actually notice a benefit by doing so.

Same question with respect to cutting/grinding side electrode so the spark jumps the side of the center electrode as opposed to the very bottom.

Just day dreaming.

[dubois]

I was ready to change my plugs yesterday and I was looking at some (out of my inventory) that were used for a M50 engine and noticed that they have two electrodes, and got me thinking along the same lines. Also I noticed that old plugs were burning only 270 degrees!

I know that little spark can make huge difference on performance, but other than dyno testing, I haven't heard of a empirical way to test it the effect of different plugs. I would love to see a "study" with real data on M10.

I also know that using M50 plugs on M10 would be a very bad idea. (the ignition system is totally different and the diameter of the plug - not the threads is smaller)

[AlanM]

Some years ago when I had a fairly heavily modded M10, I tried using Splitfire plugs over standard NGKs. On the dyno this produced 4 more Hp at the wheels. Both sets of plugs had been indexed to the chamber.

Part of this gain I believe was also in setting the gap to 35 Thou, over the 28 Thou on the NGKs. I had a Crane XR77 with an MSD 6AL which helped of course to fire the larger gap.

I was running 100/130 Avgas which has a slower flame front, and had a huge lump in the piston which also slows the flame front meaning I needed quite a lot of ignition advance. 23 degrees initial. 43 total

Perhaps the 2,3 or 4 electrode plugs would be more effective again.