Spark plug gapping vs. boost

[boostjunkie]

Found this information on gapping WRT boost levels here: http://www.anythingsubaru.com/articles/article001.html

I might have to change the gapping on my plugs (currently .43"). However, aren't the subaru gapping tolerances .38-.43? With this chart, I'd need a .22 gap!!!


SPARK PLUG GAPS AND BOOST LEVELS

It has been found that if boost levels pass 1.2 bar, then the spark plug gap should be closed down. Look at the chart below.

1.2 bar Ngk pfr 6b9 .9mm or .035"
1.25 bar Ngk pfr 6b9 .8mm or .032"
1.3 bar Ngk pfr 7b9 .7mm or .028"
1.4 bar Ngk pfr 7b9 .65mm or .026"
1.5 bar Ngk pfr 8b9 .55mm or .022"

It has been found that the rapid pressure change in the cylinder can, in high boost applications, shift the spark off the end of the plug and cause a misfire.

The early model pre - 1997 cars are only rated at 1.1 bar of boost. Post 1997 are rated at 1.3 bar.
In some countries, differing weather conditions can denote hotter or colder spark plugs. I use NGK spark plugs and this is only a guideline based on standard models.

Regards,
James Laird

[IggDawg]

I'm running 0.7 bar. Not much over stock. I was feeling some hesitation at part throttle. not like I was before with the misfires... just some mild hesitation that could have been mistaken for road roughness. I tried closing the gap from .040 to .035, and it cured the problem. part throttle is smoother than ever. much more consistant performance too.

[boostjunkie]

Re-gapping is on my list of things to do this weekend (now that it's finally getting warmer out!!). I have the plugs gapped at .43 right now. There's that "roughness" that you're talking about, so hopefully the gapping at .35 will help.

[Legacy777]

wonder what this would do for n/a cars.......tighten up the gap a little.

[boostjunkie]

I'm not sure what effect it'll have on the N/A cars . . . but for those that don't know (I'm sure you two know about this) . . .

Larger gap - larger spark which promotes better/complete burn of a/f mix . . . however, there's the possibility that a gap too large will cause the spark to be blown out.

Smaller gap - smaller spark which might not be able to completely burn the a/f mix . . . however, the chance of the spark being blown out is minimized.

Just thought I'd share what I "think" I know. Lemme know if that info's incorrect.