Dexter@tirerack

I spent last Saturday changing the plugs on my '02 WRX with about 60k miles and found the info on ScoobyMods.com to be a nice help. I just assumed that I could walk into my local Napa and get some plugs and go for it. Turns out they didn't have anything so I went to another store who ended up having an Autolite "Double Platinum" that I thought would suffice.

I ended up installing/removing/gapping them three separate times before giving up. The engine was missing like mad and the CEL was staring me down. I ended up cleaning and regapping my original plugs and reinstalling them with great results. I plan on using them now until the car starts to hesitate again.

Q: Has anybody had a great experience with another plug that might last 60k miles or so? What was the best gap experience (recommendation) with an all stock engine? I'd love any sort of improvement over stock plugs with few or no side effects

mmboost

iTrader: (2)

I think many people are using the Denso Iridiums... and generally the local Kragen doesn't have these. You can order them from many of the vendors who frequent I-Club.

jason

andyhidley

HUhhhhhh... I'm using Autolite "Double Platinum"s and I have not had a CEL since....Car runs fine.... R U sure that you had the electrical connections "snapped" on tight?

Dexter@tirerack

Absolutely. What did you set the gap to? Any engine mods?

andyhidley

I set the gap at the factory setting, whatever that was.. I also set it kinda tight at that factory setting..

You see the more boost that the plug is under, the harder it is for it to spark. If you left them at the out of the box settting, (.080?) it would run like crap.

As for mods : I had a turbo XS unichip, KN air filter, bigger exaust, removed air box, and ran 16-17lbs of boost. It ran great.

Since then, about 10K miles, I have removed the unichip and am back to stock levels of boost.. I'm looking for longevity........Plugs still work great and I have not yet had a missfire CEL. Or any for that matter..

international B

iTrader: (5)

i would say use ngk plugs... a japanese plug for a japanese car, just get one step colder then the stock ones.

Dexter@tirerack

I think they are boxed with about .04" gap. I tried .035, .025, and .020 - all with similar results. They might've worked had I tried some more in the .020s, but it's tough to wait for the engine to cool between attempts and patience was running low...

The car is running great with the refurb'd stock plugs. It feels like new again - but not sure how long it'll last. What's the part number again on that "colder" NGK? Platinum? Iridium? What makes a plug "cold?"

andyhidley

I used Autolite double plat - part number APP 3923. Is that what your using? this is the direct replacement for stock.... But because different plug manufacturers differ in their heat ranges. This is actually 1/2 a heat range colder than stock

Dexter@tirerack

That's the one I couldn't get to work. What is meant by "colder" when referring to plugs?

Dexter@tirerack

Here's a link showing the difference between and reasoning for hot and cold spark plugs.

andyhidley

When the plug sparks, and ignites the fuel, the fuel burns and generates heat. Some of this heat is required to burn off carbon deposites that accumulate on the sparkplug. Too much and the plug and/or piston melts. Too little and the plug fouls and misfires.

So if your adding "performance" mods which "actually work" , then your making more horsepower, i.e. more fuel is burned and more heat is generated. So to maintain the same spark plug tip temperature as stock you will require a colder plug. This is achieved by having more or less "insulator depth " in the plug. Basically its allowing the H2O in the cooling system to extract the heat. Move the insulator farther or nearer to the water and its is easier of harder for the heat to move into the cooling system.

The How things work link is exactly correct!!!

Dexter@tirerack

Thanks Andy. So the moral of the story: Stay with stock temperature plugs if there aren't any real engine mods.

I've always been a grease monkey, but it was with naturally aspirated engines. Spark plug gap was never much of a concern - they worked fine right out of the box. This WRX, however, is a different story. This topic is beneficial to the board because it takes an hour to get to the plugs and it can burn a weekend if you don't understand the details of plug configuration on this turbo engine.

To continue the discussion, has anyone tried a colder plug with a stock engine setup?

DeliciouSpeed

iTrader: (2)

I'd never run anything other that NGK or Denso plugs in the baru myself. I've noticed american plugs don't run well in J cars-well at least in my experience.

You'll have to tell us more about your set up before we can recommend a plug.

Dexter@tirerack

Bone stock.

andyhidley

Alittle bit of info on plug gap:
It takes 100,000 volts to jump a gap of .125 inches at atmospheric pressure. So in a N/A motor you could probally set your gap at about .080(give or take alittle) and have it not misfire while using about 100,000 volt ignition.

Now when you use "forced induction" turbo or super charger, you probally will have the same voltage. So to prevent misfires at one bar of boost (one atmosphere = 14.7 lbs) you would have to cut the gap in half because you are doubling the air pressure in which the plug has to spark in.
and so on and so on..... more and more boost = smaller and smaller gap OR more voltage.......