Adam S

I just got back from vacation with the GF after installing a set of Denso Iridium plugs. I logged 184 miles on the A4 on a drive that I have done three or four times over the past three years. I used 7.3 gallons for the round trip. My best average fuel efficiency with my stock NGK plugs was ~22mpg. The trip was about 50% freeway, and 50% country highways with some stopping, traffic, hills, etc. This also included a trip over a mountain where I was pushing the car quite bit. The trip was from the North Bay Area to the Clear Lake area near Middletown, CA.

My fuel efficiency on this trip with the Denso plugs was just a hair over 25mpg. That's a 3mpg improvement. If I were doing all freeway driving, I think these numbers would have bumped up to 27-28mpg, maybe a hair better.

I suspect that a brand new set of stock plugs would have improved my fuel efficiency over the old carbon fouled plugs, but you never know. A better test would have been to install new stock plugs and compare them to the Iridium plugs.

I've always been suspect of the low fuel economy numbers on my A4 Avant. I was convinced it could do better. I even complained to my dealer but they were no help. I was rationalizing my poor fuel economy with "wider rubber, grippier rubber, the chip, etc." The only time I've come close to this kind of fuel efficiency was on a trip down Highway 5 to LA. I had a .8 bar Autothority chip at that time and got 24mpg on the trip averaging 75-85mph.

Oh yes, and power delivery is definitely smoother with the new plugs. Again, I don't take any of this as absolute evidence of the benefits of the Iridium plugs since my stock plugs were somewhat fouled after 15k miles and 1 1/2 years. So this is all anecdotal evidence. At best, it tells me that I needed a new set of plugs.

Some of you may not care about fuel efficiency - that's OK, but I do. Mostly it's the idea of getting the car to run at it's absolute best. I think I can say it's doing that now. :-)

My next report, for anyone who cares, will include my around town mileage.

Ferris TMK

Thanx.. I will be doing some testing on these as well..