Put a set of NGK Iridiums in and I think they are great.I did notice better over all performance.I know some like the Denso plug and they are a great plug.In some cases they minght be the only plug to use.But check the NGK plugs out.For under 7.00 dollars a great plug.This was the first time I changed plugs in my L I did it in under an hour and a half.I was given an address to check out I thought it was good so I will pass it on.Here you go.
http://ngkaz.home.att.net

 

Here is a better link

http://www.ngksparkplugs.com/products/

right now they only have a cross referance for the TR5
which is TR5 IX part # 7397

So for anyone using a TR6 or a BR7 you are out of luck

 

TR5 IX part# 7397 =$6.72 each at Carquest. You do the math.

NAPA wants $8.49 for 7164 which is TR55 IX.

I think the difference between the TR5 and TR55 is the gap. The TR55 is around .050".

 

I bought the TR5 IX #7397 Iridium plugs yesterday and installed them last night. They were $57.52 tax included at Carquest.

I did a few WOT blast and normal driving last night after the install. I checked a plug this morning and they look perfect. They are a light tan almost gray color. I took pics to be posted when I get a chance.

The idle does seem smoother and at cruising speed it might be smoother (it's hard to tell for sure on that one). The test will be do they idle just as smooth in a week. New plugs always idle smoother then start getting that intermitent miss after a short time.

As far as performance, I can't tell. The track will let me know on that one. Most people that notice a difference with Iridiums are replacing stock plugs or bad ones. The TR5 IX feels just as snappy as the regular TR5. When you go from a hotter plug to a colder plug you will notice a loss in throttle response like MRBBQMAN did going from the Splitfire's to the colder IT20 Denso's.

 

Thanks for the info Mr. Chuck I bought a set of the IX's yesterday to try out. It'll be interesting to see if they're worth it.