I ordered a set of Denso Iridium plugs with stock heat range.
I had good experience with these at my previous car, so I would like to try them in my EVO too.
I read some article about the gap of the plugs, and it basically says "bigger gap is better, but requires higher voltage". Because rich fuel/air mixture is harder to ignite, usually turbo applications have smaller gap than NA ones.
But according to Denso, their 0.4mm iridium tip, and U-groove electrode design can reduce the voltage requirements, so the pre-gapped 0.044'' gap is supposed to be fine with stock engine. But they say we can gap it if we want.
I think I will try with 0.044'' gap with Ralliart spark plug wires. (They suppose to deliver more voltage to the plugs) If it's not working, I will re-gap them later.
Here is the article from Denso FAQ list.
Q. Do I need to set the gap?
A. Generally, no. The DENSO Iridium Power plug comes pre-set with a protective sleeve over the firing end, to protect the gap from accidental alteration. DENSO Iridium Power’s ultra-efficient firing power compensates for normally recommended gap settings that are smaller than the pre-set value. In the cases of vehicle modifications (nitrous, turbo-chargers, super-chargers, high power ignition systems, etc.), some adjustments may be desired. Or, if you prefer to remain consistent with factory specifications, you may adjust. However, please be careful not to place any stress on the fine center electrode during adjustment. You could accidentally break off the very hard, and therefore brittle, tip.