I know alot has been written about this subject but I thought I would share my experience. First off I have a relatively mildly modified MR2 Turbo: it has a MBC set to 14 psi and a re-programmed ECU by G-Force. It also has a HKS Super Power Flow intake and a Genie cat-back exhaust. It has 77,000 miles and I am the original owner (bought it new in 1991!). It is in outstanding shape (never seen snow, hardly ever has seen rain) and generally runs quite well.
I have been using NGK BKR7E coppers for over 7 years and gap them with a stock gap of about 0.031 inch. The engine generally idles smooth, doesn't mis-fire, and boosts fairly smoothly. I change out the coppers every 3000-5000 miles and when I put a fresh set of copper plugs in I notice a slight increase in performance via the "seat-o-the-pants" meter: slightly faster revving, less time to full boost when in 5th gear and the pedal floored.
In any case, I decided to give the NGK iridiums a try (BKR7EIX). I kept them at their stock gap with is the same gap as I set the coppers. The BKR7E that I replaced had about 5000 miles on them and it was clear the center electode was rounded showing some modest wear. When I took the car for a test run after installing the iridiums I was expected the usual slight performance boost but the car felt exactly the same as with the old coppers. I realize the seat of the pants is not very accurate but I was a little disappointed. I did notice a bit of an exhaust smell (my exhaust is stock except for the muffler) when I did the WOT in 5th gear test and the boost was ok but definitely not any smoother or faster to build than with the old copper plugs. After a few runs I noticed a bit more soot on the exhaust pipe than I normally see.
So the bottom line is the iridiums seem to be ok - I was a little disappointed not to get the "fresh plug" effect. It would be interesting to see if I switch to a set of fresh coppers if I'd notice anything different, but for now, I'll stick to the iridiums for at least a few weeks to see how things go.
I have been using NGK BKR7E coppers for over 7 years and gap them with a stock gap of about 0.031 inch. The engine generally idles smooth, doesn't mis-fire, and boosts fairly smoothly. I change out the coppers every 3000-5000 miles and when I put a fresh set of copper plugs in I notice a slight increase in performance via the "seat-o-the-pants" meter: slightly faster revving, less time to full boost when in 5th gear and the pedal floored.
In any case, I decided to give the NGK iridiums a try (BKR7EIX). I kept them at their stock gap with is the same gap as I set the coppers. The BKR7E that I replaced had about 5000 miles on them and it was clear the center electode was rounded showing some modest wear. When I took the car for a test run after installing the iridiums I was expected the usual slight performance boost but the car felt exactly the same as with the old coppers. I realize the seat of the pants is not very accurate but I was a little disappointed. I did notice a bit of an exhaust smell (my exhaust is stock except for the muffler) when I did the WOT in 5th gear test and the boost was ok but definitely not any smoother or faster to build than with the old copper plugs. After a few runs I noticed a bit more soot on the exhaust pipe than I normally see.
So the bottom line is the iridiums seem to be ok - I was a little disappointed not to get the "fresh plug" effect. It would be interesting to see if I switch to a set of fresh coppers if I'd notice anything different, but for now, I'll stick to the iridiums for at least a few weeks to see how things go.
