hmm, what about the silver spark plugs from Nology? Havent' seen any mention about those. They claim that silver is the best electrical conductive metal there is.
http://www.nology.com/silver.html

 

Platinum plugs were originally developed for use in sports prototype racing cars. Not because they worked any better, but because the engineering compromises required for ultra performance and aerodynamics made changing plugs a nightmare- it could take days to tear into the car far enough to get at the plugs... so the platinum plugs lasted a lot longer, keeping the vehicles more race ready...

Which is their chief advantage today, and also for iridium plugs. It's not about performance, but about longevity. Iridium plugs properly gapped might last the life of the engine, particularly with low deposit unleaded gas. Which means they'll save money in the long run, particularly considering the price of labor.

I'll agree with aychyse7en about NGK plugs in general. Their standard copper core plugs are excellent for people who want to tinker with their cars, giving good life at a low price point. I owned rotary engine mazdas years ago, and they'd gobble up any plug that wasn't NGK, and I've used NGK's on everything since, including my last car, a turbo intercooled volvo... never a problem.

I'll probably go with a set of NGK iridium plugs when the stock Densos need to be replaced- I like driving my box a lot more than tinkering with it at this point in my life...

People need to remember that the box's ignition is a system, really pretty highly engineered. Multiple coils make it a lot more forgiving in the sense that coil failure won't leave you dead on the side of the road, but that increasing plug gap will increase coil stress due to the higher voltage needed to create the spark... that's a long term consideration, for sure, but worthy of note at this point...

 

from what i know, platinum and iridium can stand higher temp and last longer, but thats only useful in sports car or racing applications where the engines are under tremendous heat and pressure. for a regular car like xb, cooper plugs will conduct better and cost alot less, like the ngk v-power.

 

so what is the recommended mileage to change the plugs on the XB? I've got 72K + miles on mine.

 

30k. intervals

 

I may have to double check this on the TIS site at work but I believe all Scions, Toyotas, and Lexus vehicles are equipped with Denso Iridium Tipped spark plugs and don't need to be replaced for 120,000 miles. Why would anyone be stepping down, other than cost issues, to lower spark plugs that affect your fuel economy. Yes I am a Toyota Technician.