The advantage of good plugs is HIGHLY debatable. Longer service life is usually the most agreeable advantage. The design in the plug does promote a good burn of the fuel mixture as oppose a more standard plug. A good complate burn of the fuel will increase effeciancy, which increases mileage and power a small bit.

Persoanlly, I think one step cooler plug wouldn't hurt even on the MC. As long as they were a GOOD plug, like maybe the Denso Iridium Powers.

 

Since I was at the parts store anyway and have been feverishly changing filters and cleaning up my newly purchased 04 MCS (19,000 mi stock and have no idea how it was driven)...decided to change out the plugs as well. Went for the NGK Iridium which were readily available.
1) the Orig Plats were carboned up, indicating a lot of low RPM driving (IMHO) Nothing to indicate a problem though...The insulation around the electrode was a nice normal light brown color) and yes, I have a torque wrench!

2) I always chg plugs at 20,000 mi anyway...Like others have said...to heck with what the dealers say. This is a 4 cyl and it is not like you have to put a second on your house to get plugs (or oil chgs for that matter) I still chg my oil, synthetic or not at 3-4000 mi...It is the filter I worry about.

BOTTOM LINE...MINI Idles smoother and is more "eager" than before with the new Iridiums....SOLD!

I have been told by my auto Mechanic (who I have known for 20yrs and only sees my cars when I cannot do the major work myself) that Iridiums vs Platinium is like synthetic oil vs normal oil...both work...JUST ONE WORKS BETTER! For a few dollars xtra I recommend the Iridiums

 

If I can add to the questions...when you do the change to higher end plugs, have you done the wires also, i.e. to magnecors? And does the Plasma Booster do what it advertises in addition to the better plugs, wires, etc.? Just got my cooper and looking to work it up a bit.

 

All, I'm putting on a Screaming Demon coil, with Livewires, and Nology Silver plugs today on my 06 MCS. I'll let you know how it goes. Check out the Nology site. They claim if you are using anything platinum or iridium your not getting the performance you think you are.

http://www.nology.com/silver.html

I've used silver plugs in the past on my 97 Type-R and they made a huge difference over the platinum plugs.

...update at 11

 

In a word... WOW!

A major, noticeable difference. Clean, smooth, with evident improved acceleration.

Thanks for the great advice and instruction on this thread! My advice back to this thread is do some research on your touted Iridium and Platinum plugs. You're not getting what you think you are!

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’06 MCS, Chili Red & Astro Black, Black M7 Extreme Hood Scoop, BMP Performance Intake, PROMINI Front Stress Bar, Pilo-Racing Rear Stress Bar, Screaming Demon Coil, Live Wires, Nology Silver Plugs (D4YS)