Can someone help me out? I had my spark plugs gapped to .35 and I was miss firing. I gapped them to .40 now and my car is misfiring even more than it was when I had my plugs at .35. I have have the following mods for my '06 cobalt SS/SC: CAI, Vibrant Long tube headers, Corsa exhaust, 60# injectors, Stage 3 pulley, Stage 3 H/E, Dual pass w/reservoir, A/F gauge....I have the Autolite XP 3923 plugs in now. Can someone enlighten me on the correct plug and gap that I need. Thanks!

NGK BRK7E comes to mind but I'm not sure if that is correct. Spark blow out is usually what plug gap effects. If you are getting misfires I'd look into testing the coil packs

How do I test the coil packs?

The way I have done it before is to get a good one, from a friends car and just try one cylinder at a time

Thanks for the quick post/info!

Can anyone provide any other info as to what plug and gap I should run with the mods that I have?

Purpose of the Metal

The metal in a spark plug serves a single basic purpose: to channel the electric energy from the plug wire or coil pack through the spark plug so that it can be forced to the engine block in the form of a spark. Therefore, any metal that conducts electricity at all could potentially be used for a spark plug. The metal should also not get too hot; one of the main problems with some metals is that they overheat quickly, causing the electric charge itself to be compromised and the spark plug to not operate as smoothly



Copper Spark Plugs

Copper spark plugs are generally considered to have the best performance of any spark plug type. This is potentially different from what advertising companies suggest, but the other metals are, unfortunately, not as conductive in general as copper is. Platinum and iridium plugs are more likely to overheat, which causes damage to the plug components and can compromise the delivery of the spark to the engine block.

Platinum and Iridium Plugs

Platinum and Iridium plugs perform at a lower level than copper spark plugs, because they are less conductive and they tend to overheat. However, the overall longevity of these two types of metal is better than copper plugs. In reality, copper has the best performance of all three and the worst longevity. Platinum has good longevity and the worst performance. Iridium has good longevity and a performance that is decent, which is why iridium plugs tend to be more expensive than any other type. Still, the difference between these plugs in terms of overall quality is minimal, as there is a trade off for each.

Most copper plugs need to be changed every 20,000 miles or so. Platinum and iridium plugs can often go for twice that before they require changing, but the overall performance will not be as good and you may have to deal with overheating of the plugs. This is potentially not worth the added cost of both platinum and iridium spark plugs, although the decision will depend upon your preference.

For your mods 0.032-0.033.