Has anyone seen any improvements such as smoother idle or better gas mileage with hotter plugs?

 

Yeah, do a search or just check out the strange deposit on plugs thread above. I had the hotter plugs installed, but I had lots of idling problems and misfiring, and I definitely had fouled plugs so the clean plugs were a big help. Check the Tech forum. There are some good thread there as well. If you do not have idling problems or anything to make you think that you need new plugs. Don't do it. It isn't for you. There is a potential down side to hotter plugs such as cracked insulators. It is generally considered smart to run the coolest plugs that won't foul.

 

This example is from the 13B turbo in my Luce. Auto, doesn't get revved all that hard. Characteristics similar to many RX-8 drivers (Auto & manual)

Swapped the B7 + B9 combo for B6 + B8 combo. the hotter range plugs idled better & didn't foul quickly like the 7+9 combo.

The drawback is in ultimate performance. With the hotter plugs, the engine now has the rare "ping" at full boost around 6000rpm.. To compensate, I had to drop the boost by 0.05 bar.

In this case, the gain was worth the pain.

Have done the same for several other RX-8 owners so far aswell. They just putt around. The obvious tell tail is the leading wearing far quicker than the trailing.

I.E, you aint revving her at all.