Hank Hill

I've been thinking about going to some Iridium plugs so I can change my plugs once and not have to worry about them again for a long time, and it looks like Denso and NGK make the best ones out there.

I've heard that Denso plugs are the "best in the world," but the thin 0.4 mm electrode can supposedly wear out quicker than the 0.6 mm electrode used on the NGK, so the NGK will theoretically last a lot longer (one of the characteristics I'm looking for besides good performance). And I wonder if the AC Delco Iridium plug is any good...

I don't really care about cost, and I know the NGK TR55 is the preferred plug on this site, but I'd like to know which Iridium plug is really the best. And what about Web sites where there's scientific testing of spark plugs, and not just testimonials like "I've always used Acme plugs and never had a problem..."

Hank Hill

I was just checking the fitment charts and it looks like NGK doesn't have an Iridium plug recommended for the '99 LS1, but Denso and AC Delco do. NGK specifies the "Laser Platinum PZTR5A-15" for my LS1, but they show no Iridium equivalent. What's up with that?

WILWAXU

iTrader: (6)

I'm sure there are other plugs out there that work.

But, I know the TR-55's work well.

M6HuggerSS

i would like to see some dyno comparisons

Cheatin' Chad

iTrader: (3)

TR55IX= I am using this Iridium plug in my 98

Ferocity02

iTrader: (60)

Dyno numbers? I difference would be minimal, fraction of a horsepower at the most. The differences are mainly in lifespan and gaps, different gaps for F/I, N/A and N20 and what not.

Cheatin' Chad

iTrader: (3)

I think the difference would be so small that you couldn't rule out dyno variance.

Unless you are going to a bad set to a new set.

Slowhawk

iTrader: (12)

Alot of people have good luck with Denso but I've personally seen 2 problems with them not running right.NGK'd are $2 a piece and have never had problems with them in all of my customers cars.So I vote NGK...Use what works.