What's the affect of differing Spark Plug Gaps?

[GiJOr33]

I was just wondering what affect changing the spark plug gap has on performance? I mean if you're getting a miss fire then you gap the plug smaller so as to reduce the resistance against the spark. Why not just leave it small to begin with? What's the advantage of a bigger spark. I've heard that you get a better burn, but once the fuel/air mix is lit then surely the burn is the same (fuel type dependent).

The reason i ask is because i had to gap my plugs down a little to get rid of a slight missfire under boost. What can you do to allow the spark plug gap to be big but no miss fire? Is there anything that can be done apart from an ignition amplifier?

Cheers,

Andrew

[mokompri]

decreasing gap size reduces the amount of energy needed to ionize (spelling right?) the air to create a spark, so if your getting misfires and have to reduce the gap then your ignition system cant ignite the mixture under the conditions where misfiring occurs

the larger the gap you have, the more of the spark energy is passed onto the air fuel mix and gives you a more even burn as the flame front gets a better start, and yes there is a point when too much does nothing for power

[The Mafia]

well, higher boost means the density of the air in the cylinder is higher, hence creating more resistance between the spark plug gaps.

Then more energy is need to ignite them. You could either get some sort of a booster to make a stronger spark, or close your gaps so they are close thus requiring less power to mark the contact arc to ignite the fuel.

[GiJOr33]

you suggested close the gaps more... but what is the detriment to performance? i mean surely closing the gap has to hinder it somewhere otherwise all cars would have an 0.5mm gap.

[Gav]

The main downside to a smaller gap that I can see is the increased likelyhood of fouling(carbon deposits joining the tip to the electrode, thus no spark at all).

This is the reason that I no longer use platinums, as when I used a smaller gap, I still had to remove them regularly for cleaning anyway.

Use coppers in the correct heat range for your application, gap to 0.8mm and check/clean/replace regularly. Oh - and don't use octane booster if you can avoid it - it deposits a coating that also encourages fouling.