Re: How important is spark plug gap?
Personally, on gas I run an NGK cold v-type plug at 0.9 with MSD and a bosch coil (the little black transformer type).
The gap makes a difference (in theory.....). The bigger the gap, the more power required to jump the gap, hence the spark ends up 'hotter' but shorter. Close the gap, and you get a longer 'cold' spark.
Now, all that was fine 20 years ago. We now have high energy coils, v-type (splitfire) plugs, MSD, etc, etc..... so the theory goes out the window.
How many people 'in the game' have pulled plugs out that are worn to a knife point with about a 1.5mm gap?? These cars are still going without any sign of a miss. Mind you, the coil is being pushed to the absolute limit to maintain a spark. Put plugs like this into an XW (or similar) with the original points ignition and a 12 volt coil and it will be lucky to start, let alone run smoothly.
My two cents.....