Gapping Iridium Spark Plugs

Suzuki shop manual recommended spark plug gap for the Suzuki Swift with K-Series engine (K12B, K14B) is 0.95 to 1.05mm (.37" to .41"), but both Denso IXU and NGK Iridium IX spark plugs come pre-gapped from the factory at .76mm (.30"). While this is not a cause for worry and these Iridium plugs do work very well straight out of the box in the Suzuki engine and with proper gap these plugs should work even better. As the gap increases more spark energy is required to bridge the gap and this is not good for the ignition coil. Iridium plugs with their thinner electrodes needs lower spark energy to jump off and bridge the gap, because of this lower energy requirement i believe it should be able to fire reliably even with a wider than factory recommended gap without straining the coils.

I changed to Denso Iridium Power IXU22 spark plugs from the stock NGK KR6A-10 as soon as i bought my Swift, but then i put the plugs in as it is at their preset gap of .30". Eventhough Iridium plugs are long life no maintenance plugs i decided to try some NGK Iridiums as i got a set of 4 for really good price, the car has done 19400KMs, barely any distance to wear out the older Denso Iridiums. So when i make the switch to NGK I decided to gap the plugs to .45".

Here is a good read (PDF) on Understanding Spark Plugs by NGK

Denso has to say this: "Ignition by electrical spark occurs because the fuel particles between the electrodes are activated by the spark to discharge, a chemical reaction (oxidation) is triggered, the heat of reaction is generated, and the flame core is formed. This heat activates the surrounding air-fuel mixture, eventually a flame core is formed that spreads the combustion to the surroundings itself.However, if the quenching effect between the electrodes (the work of the electrodes absorbing the heat and extinguishing the flame) is greater than the flame core heat generation action, the flame core is extinguished and the combustion stops. If the plug gap is wide, the flame core is larger and the quenching effect is smaller, so reliable ignition can be expected, but if the gap is too wide, a large discharge voltage becomes necessary, the limits of the coil performance are exceeded, and discharge becomes impossible."

Gapping Iridium Spark Plugs

Common knowledge when it comes to gapping Iridium splark plugs is "Don't do it". Its is very rarely recommended to gap Iridium spark plugs, the reason is the thin laser welded Iridium center electrode is fragile, and with a wrong move its easy to snap it off or crack its weld. NEVER EVER use a SCREWDRIVER tip to gap a thin electrode Iridium spark plug! It is recommended to use a proper gapping tool or a thin nose pliers to set the gap. And when doing it take your time and take care not to touch the center electrode.

NGK Iridium IX DCPR7EIX Gap .30" Done 13000KMs from my previous Suzuki Astar (K10B Engine), gap as good as new.

Denso Iridium Power IXU22 Gap .30" Done 19000KMs in my Swift, barely any wear.

Brand new NGK Iridium IX DCPR7EIX with gap set to .45"

Spark plug gap measuring and gapping tool. This tool is made by Powerbuilt, and i don't like the gapping bit because the metal piece is not sturdy. Measuring bits are good enough.

Nose pliers can also be used to carefully pull the ground electrode strap, but be careful and thinner pliers would be even better.

NGK Iridium IX DCPR7EIX. New gapped to .45" on the left and old with factory gap of .30" on the right.

Set of 4 and Set of 3 (old) NGK Iridium IX DCPR7EIX and Set of 4 Denso Iridium IXU22

References:

http://www.ngksparkplugs.com/docs/tech/racing_spark_plugs_performance_applications.pdf
http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/spark/index.html

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Update - March 12, 2014:
After two days of city drives with the gapped Iridium plugs i have noticed a very slight improvement in torque from 2000 RPM. No negatives noticed with wider gap so far, starts and idles the same. I will update on the high RPM performance shortly.

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Update - March 13, 2014:
No high RPM misfires or loss of power noticed. Torque has definitely increased and is noticeable. Highly recommend doing this if you decide to put in Iridiums.

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