Premium and Super Premium Spark Plugs

I was wondering what Premium (platinum/double platinum) and super-premium (iridium) spark plugs do for performance? Does anybody know of any facts that say they imrpove gas mileage or engine efficiency? What are some good brands of premium spark plugs? Autolite? NGK? Bosch? Denso?

All they do is last longer, which is a big advantage in todays vehicles where a tuneup can be a full day's job. I always use whatever the manufacturer recomends. A/C Delco for GM, Autolite for Ford, Champion for Chrysler.

its true. the only reason to change from what came from the factory, is if your using a high boost/nitrous equipped car it might be beneficial to get a colder spark plug to keep knock in check.

I installed Denso iridiums in my turbo Lotus. They have a finer center electrode than the NGKs which is better from a voltage requirement standpoint. Since I run about 18 pounds boost, plug life is also a major issue which the iridiums address well.
I have been pleased with the NDs so far...

I use NGK and Denso exclusively (especially on my bike). The others are crap, and that multiple electrode bullshit is just that.

I stick with the copper plugs because they're inexpensive and I change them often enough that it doesn't really make sense to spend the buku bux on the unobtainium plugs that last for 4.2 million miles. Then again, my plugs are relatively easy to change. I suppose if i had a real PITA car (like a transverse v6 or something silly) then i might get the longer lasting ones.

I stick with the copper plugs... I change them often enough

Something that works great if you change them every 20k or so, and if you have a drill press or metal lathe:

Bend the outter electrode out of the way and drill a "dish" into the center electrode with a 3/16" drill bit, don't take much material off, just cup it a little bit. Bend the outter electrode back into place and gap it to spec. Drill a hole in it (I think 1/16") directly in-line with the center electrode. (Use cobalt or better bits for the outter electrode or you'll be using a bit per plug) This creates a spark that is "focused" on the hole in the outter electrode, and the spark shoots out through the hole like a pencil-torch. The funny thing is that when the 2- and 4-electrode plugs came out, they were trying to get the same effect as this in a design that couldn't be copied at home... and their design doesn't work as well as this... it's just a knockoff of side-gaping plugs. It speeds the flame front a bit and seems to work... although it may just be a psychological improvement, I've never had anything on a dyno. Just be sure to change them every 20k or so, otherwise the outter electrode will wear away and the part past the hole will fall off into the cylinder. The next time I do this, I'm going to grind the electrode off past the hole so that the edges past the hole are the same thickness as around the hole, so if I do go over mileage there's nothing to fall off.

One thing to remember; the best spark is the most consistent spark. For that reason I recommend against spending money on multiple-anode plugs like the splitfire or E3. Just use a good old-fashioned single-anode plug. Multiple grounds means that the spark jumps around each time. While it may seem like a good thing, the 1/4 difference is a big deal when you're talking about flame front speeds in milliseconds.

I chose Bosch... not necessarily because I think they're the best, but because they have been the most consistent. I've had a lot of vehicles on an osciliscope, and bosch plugs return the most consistent waves of any plug I've seen. NGKs do well also, but not quite as well in lower-voltage classic cars. AC Delco plugs seem to do remarkably well in those applications.

I have a 1973 chevy 454 that I used AC Delco. AC quit making that part number so I switched to Autolites. My 96 LT1 has Bosch Platinums, but I've run NGKs in it as well with equal success.

well, for my two cents worth i have to agree with j-ri, my experience with drivability issues has taught me unless your running something highly modified, turbocharged etc, the best plug is the factory recommended plug if its still available with the exception that i would recommend motorcraft for a ford has i feel the quality of the autolite went to hell after ford sold them off. most newer vehicles have gone to a platinum plug because of the time it takes to tune a newer vehicle. (tuned a ford expedition lately?) you may be interested to know that while champion has been the chrysler plug for eons it seems . they have actually gone to using ngk plugs in the last couple yrs . thats my two cents for what its worth.