Re: plug gap for denso iridiums?
standard is 1 - 1.1...but the ignition seems to cope up to 1.5mm (no misfire)....i haven't tried any further. (EL GLi 6) This is with standard Motorcraft plugs.
Supposedly by increasing the gap, a minor increase in power/responsiveness is available, if your ignition can cope. The way those pointy electrode iridiums are made, you can increase the gap a fair bit more due to an effect a "sharp" point has in how easily current flows into the atmosphere. (sharper point means that a charged plate will discharge into the air reasonably quickly.) If this is used in a spark plug, it is far easier to make a spark across the gap. Therefore the gap can be wider. This is prolly why they came in at 1.3mm when rec. is 1- 1.1. Testing on normal plugs (by me) suggests that iridiums could be alot wider than 1.4-1.5mm and still work well...up to you to experiment...Another way to increase power/responsiveness/smoothness/fuel economy is to face the open side of the plugs towads the exhaust valve (at nine o'clock when completely screwed in.) This can be done by swapping the plugs between the holes and/or using special plug spacers. Its up to you how far you want to go.
1987 Jaguar Sovereign - Metallic Green
3.6L DOHC 24 Valve