Denso Iridium Plugs

Rating scale is from 1 to 10. Low being 1 high being 10

Rating: NA
So far several aspects of the plugs have yet to be tested, so the rating may change at a later date. Denso is the only plug I know of which advertises a HP increase with their plugs. There are a lot of claims made, but so far these plugs are living up to all the hype. One claim Denso is proud of is their "five rib design". I can attest to the effectiveness of their rib design. In fact due to it, I was unable to use my 5/8 spark plug socket and had to opt for a standard socket. The problem arises when you try to remove the socket from the plug. It separates the socket leaving you with the wrench and the extender while the socket remains firmly attached to the plug. Update: Due to problems I have changed the rating to NA.

Fit: NA

Finish: 10
Its a spark plug. There is not a lot to say about it. For what its worth though, Denso took the time to polish the whole plug. Also worth noting is Denso's laser welding technology.

Performance: 9
There are three basic concerns when shopping for a spark plug, idle quality, performance, and longevity. From what I have found, copper seems to idle the best as well as offer the best starts. The downside is copper plugs show gap erosion at around 7,000 miles. While platinum plugs last well beyond 7,000 miles, they do not perform as well as copper. This is where Denso enters the picture. Denso claims good all around performance as well as longevity with their iridium plugs. Start up and idle is at least as good as with copper plugs, and better than platinum plugs. Longevity has yet to be determined.

Note: I will publish any issues as they arise.

Update:
At just over 6,000 miles, one of the plugs snapped in half at the electrode [see image below]. Cylinder 3 also showed signs of cracks. The car is running slightly rich with EGT temps under 1300 always. Because of this I returned to conventional plugs and have not had a problem. While the iridiums did run better, I was not willing to risk another plug cracking.

Denso Iridium plugs have a much smaller electrode than either Autolite's or the OEM plugs.