gr

Yeah... I think I was one that mentioned that too!

VonK :: Retired

As to what plugs to use and why, check me on the following philosophy:

· <u>Heat range:</u> As you know, that's all about burning off any deposits on the electrode insulator but keeping the insulator from heat failure. Going too cool can ultimately lead to plug fouling. Unless they install a special wimp plug for US traffic, the stock Audi plug should be safe for long term max load on the Autobahn, a condition you'd encounter only in Nevada. So, I'd go by color inspection which shows an average of your driving habits.

· <u>Gap:</u> Designers optimized our DLI ignition systems to get the most powerful spark, consistent with practical coil pack dimensions. Today, they pack the spark with about 15 times the energy it takes to ignite the mixture, even under adverse conditions. But to get that max power, the gap resistance (impedance) must be just right, or a little less to allow for erosion. And that determines the electrode gap for optimum performance. Not that the available power wouldn't jump a ½" gap with ease.

IMHO, it's always been a myth that forced induction engines need a smaller gap. On the contrary, under full power our turbo engines operate near self ignition (detonation) often requiring only minimal energy to ignite the mixture.

· <u>Electrode Material:</u> Platinum and iridium are excellent electrical and heat conductors. Also, they are very erosion resistant, allowing very thin wires that encourage precise spark initiation while maintaining gap spacing. But, a thin wire glows easily unless it can get rid of the heat, the shorter the wire, the less its chance to glow. I understand, those plugs originated in F1, Indy, and 2 stroke racing bikes. Now most racers benefit from their longer life expectancy.

Are iridium plugs a must for the S4? Not, unless you intend to rev to 15,000 RPM for hours. I'd stick with the stock plugs and renew them yearly, unless you track your car at 2 bar with K04s. I'd go to a different heat range only if contamination is present, or the insulator looks fried. But, no matter what plug, I'd make sure I set it to the stock gap to maintain the OEM impedance match.

Whadda ya think?

Harald

Milpitas2.7T

yes all your information is correct.

However jonts on the autobahn would see less heat then a high boost run down the 1/4. Thinking that the autobahn your running a sustained speed, and not really on the boost. Just talking out loud here.

I ran one step colder plug with smaller gap on my tuned Eclipse and I was happy. After getting a few logs and week of driving, I will report whether I see no improvemen, improvement or the opposite. I am hopeful that my car will run smoother with this new plug.

But your right, my plugs looked fine, but were they performing ultimately under my situation? I won't know until I run some more logs and drive it for a week

Tory

VonK :: Retired

As for the Autobahn, you'd love it. I drove my brother's M3 there. It seems to be in the aggressive nature of Germans (where I was borne) to always have to beat the other guy. So, where there's no speed limit (and they are sadly getting more and more), everybody races everybody, and even in the M3, there's always somebody breathing down your neck. What this results in is either full throttle way up to the 250 kmh (~153 mph) speed limiter, trying to pull away from your challenger, or lifting because of traffic that, itself, is usually well over 100 MPH. Not without hazard, but the Germans are used to it. And it does get the engine hot!

Take care,

Harald

Innovator

Higher boost can require a lower gap if the ignition system is not up to snuff. It isn't really a problem when you have a coil over each plug like the S4, but many older turbos suffer from spark blowout running higher boost. My VR4 requires a much smaller gap(.30 vs stock .45) to run 18 psi or it will stumble like hell after 5500 rpm. My car had a DIS system that leaves something to be desired.

BTW, I am no fan of Iridium plugs, and I like the stock range Lasers better than anything I've tried to date.

Innovator

It is just fine at the OE spec on the S4 up to a sustained 20 psi. The S4 has an excellent ignition, and as Von said, the gap has been optimised for our specific coil packs.

Innovator

Now those are nice plugs dude. But 028? I'd go .030+ unless .028 has proven to be better..

VonK :: Retired

Agree, but I was referring to a healthy S4 system.

Milpitas2.7T

Hmm okay.. but I'm running a different style of plug, so will see.

Innovator

Yup, the S4 need nothing special done where the ignition is concerned.