so whats better, how much more mpg do iridium provide, is the extra $ worth it

Normal plugs work fine in our cars. The motors aren't really hot enough to utilize better spark plugs.

My '04 Accord EX 2.4l 5 speed manual comes OEM with irridium - NGK IZFR6K-11.

Look in your owners manual for specifics on your car.

My '01 came with NGK double plats, chances are yours did also. I changed mine at 102K and they were still running fine and the gap had remained in spec without adjustment. They're really tough plugs.

In the scheme of things: platinum and iridium are tougher metals, but copper is a better electrical conductor. Iridium is somewhat tougher than platinum and is also a somewhat better electrical conductor.

Because plat and iridium are stronger metals, the manufacturers can make the center electrode a "fine wire" which helps with igniting the mixture.



http://www.ngksparkplugs.com/apps/default.asp?nav=60000&


PS..I put NGK Vpower coppers in my 4cyl at 102K and again at ~143K. They work well in this 2.3L engine also and only cost ~$2/plug. To replace with the original NGK double plats would have been ~$12/plug. The iridiums are somewhat cheaper. I'll probably stay with the coppers since they're very easy to replace in this engine, so I don't mind doing it more frequently.
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Many manufacturers are leaning towards the iridium plugs for better gas mileage and better wear (100k+ first major tuneup, etc)... I was really shocked to find out my sister's '03 corolla actually had iridiums from the factory! No wonder why the dealers want to charge over $150 just to change the spark plugs!