Well, thats alot but I take a stab. (i`m sure I ll get worked over on it though)
1.Manufactor has a recommended choice. (that was then this in now though)
and they took all things into consideration at that time.
2.from what Ive seen its all about choice,some guys sware to one plug some guys say that plug sucks. so good luck finding an exact brand to run. Or at least one all your buds will like.
3.I always run the rec. gap but alot of guys try and open them up a bit thinking they get a longer or maybe stronger burn. Not sure I would agree you could increase performance but maybe (get more feedback on that) .
4.a wider gap causes a longer spark line wave on an iscilloscope but the end of the burn seems to be about the same where the flame out is and the coil output one plug to the next is similiar,, so you would have to think it would cause a longer burn? But would also cause overheating of the plug if it was too wide which is no good if the electrode over heats and starts to glow you can have all sorts of firing problems. I once put in 4 plugs wider gap then normal and 4 plugs narrower gap the normal on the same 350 engine on a boring summer day and put it on an iscilliscope to see the difference. It Was really hard to tell one cylinder from the other except for the end of the burn, one was more ragged then the other but the coil output (per cylinder)and oscilations where the same. Which lead me to belive it didnt matter gap wise. But hey that was just on a machine right,,,lol.
Most guys go with a hotter heat range spark plug on stock engines and on my blown car Ive heard running colder helps heat running hotter helps performance so who knows. I run stock plugs and dont know that I would gain much from anything different. Delco plugs is all I use in gm. Ford-motrcraft, chrysler -champions. In hondas ngk. I used to work for firestone and they used Bosch(not the platinum though) and they worked well in all cars. Platinum plugs seem to "fuel fowl" easier then the rest and they dont clean up very well. Which is bad news for the carb.vehicles on this site.One thing about all plug manufactures. They all advertise HP improvement with there brand. Well, if you put any plug in your car that has alot of miles on it it will automatically gain HP. DUH. Another thing I dont like about champions. They use a spring in the center of the plug!! no doubt,,crack one open sometime and look. I read an article once that said that is how they change the heat range. I read it but that doesnt make it true but I still would rather have a solid core plug in my ride. For my own ride though I will always run ac delco for "what I think" is the best plug out there. But then again like I said before good luck getting two guys to agree on what is the "Best plug" out there. My guess is your car is missfiring on that cylinder or running the coil juice directly to ground (which wont feel like a missfire it will just kill that cylinder taking the path of least resistance) and you dont even feel it, because the enging is so strong anyway and seems to compinsate for a weak cylinder. Put new plugs in it and you will sware you gained 50 horsepower with whatever plug you choose. This is how stories about one plug being better then the other get started. good luck,,,Paul.