spark plug indexing

[ohmar]

Hello Mike

Thanks for answering my questions on my motor upgrade (sefatboy). I have another for you do you or do you recommend indexing spark plugs on bikes. If so what is the best way to do it, buy a bunch of plugs or use shims (if shims are used will this effect the compression ratio). Also what plugs should be used. Is this a waste of time or will you see any HP gains.

Thanks once again

Ron

[Mike]

Shims are best and will reduce compression but not enough to be noticed. We've tried to show on the dyno a number of times if indexing helps. Have yet to be able to measure any difference, at least within the resolution of the dyno. I've also read, in various places, completely opposite recommendations for the electrode placement (most common is the open end of the electrode pointing to the most open area of the chamber). Since no one seems to be able to confirm the correct placement, tells me it does not have much of an affect. We do it on race motors because it makes us feel good and can't hurt (and sometimes to space the plug away from the piston dome, so if you have to space it, might as well index it too!! [and, yes I do know about surface fire plugs]).
Thanks, Mike