E: Engine Does anyone index their spark plugs ?

[Trickymicky]

Ensuring that the electrode gap of the spark plug faces the inlet valve. It's become a popular thing to do in classic competition. Does anyone think it makes any difference ?

 

[vibrac]

No

 

[roy the mechanic]

Like all things in "tuning" some motors will benefit, others will not. only the dyno or the stopwatch will tell.

 

[davidd]

There is no real data available on indexing a spark plug and which direction the gap should face. I have heard many say the gap should face away from the inlet valve to prevent the incoming fuel from putting out the fire. On racing engines, I note the spark plug position in my notes, but I have never had to use that information.

David

 

[fogrider]

In a book by Nicholas Swager called " Secrets of speed", there is some reference to indexing spark plug gaps : little point in a central position plug , from 0.5 to 1 percent increase in power for plugs away from the inlet valve.
So a 400bhp muscle car could ( "could") benefit up to an extra 4bhp ?
I'm not sure I'd notice that gain !

He does add it's down to how much time, effort and expense you're prepared to apply.

 

[Cyborg]

This site is useful when it comes to answering those sorts of questions. If there were worthwhile power gains, I think there would be more discussion about that part of the equation. The other reason for indexing plugs is so you can avoid having the piston close up the gap for you. Index the plug or lop off the corner of the dome.

indexing plug ground electrodes

now Ive posted much of this info before, but I recently helped tune a guys 13.7:1 compression big block chevy where the guy could not get the car to run correctly at first because he had failed to check a few clearances and on several cylinders the piston domes were barely contacting the spark...

garage.grumpysperformance.com

 

[Chris Launders]

I have noticed that the spark plugs in my SV Brough are sort of clean one side and black the other, as they are near the exhaust valve I assume the clean side faces the bore.

 

[royrobertson]

Yes. I always "indexed" the spark plugs on my 1272 cc racer. I was making solid copper spark plug washers anyway and faced the open ends of the plugs (twin plug heads and 11.3 compression) towards the centre of the heads. It may not have made any difference anyway but it was just something I did. With my Interspan ignition and extended nose plugs they were very rarely changed.
roy the racer

 

[fogrider]

I've seen Roy hurtling around Mallory on his racer , double impressive ! As Nicholas Swager says- if you're prepared to put the effort in..........

One thing has occurred to me, if a twin, still on its' KVF has its front plug ( said " weak" spark one ) indexed AWAY from the inlet valve, would that go towards a poor starting bike. ? Conversely.........?

Plus, if one was indexed away and one towards, would that make a combustion inbalance ?

For answers to this and other imponderables - tune in to next weeks gripping episode !

 

[flxible]

Have indexed plugs to face the inlet on several machines, my seat of the pants dyno detected no difference in performance.
Had also read the gains were to be quite minimal and therefore worth doing only for very competitive purposes.
For what that's worth...
Best-
George