Spark Plug Question

[ernman]

I have a 2004 Outback, and it is time to change the plugs. I did a quick search and the price ranges from $3.00 to $10.00. What would I gain with the $10.00 plugs?

[imported_dazzerjp]

I have a 2004 Outback, and it is time to change the plugs. I did a quick search and the price ranges from $3.00 to $10.00. What would I gain with the $10.00 plugs?

if its iridium plugs, then you get durability.

[Heathenbrewing]

$10 is most likely for iridium plugs. I copied and pasted the below from my posting on another forum. Copper vs. plat. vs. iridium is a touchy subject, but below is my OPINION on them:

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Some people swear by iridium plugs, claiming more HP and better MPGs, but truth be told, it is all hype and marketing. For me, I always look for independent testing and/or data analysis, not a website that is in the business of selling plugs, or any of the billion of forums that have all kinds of opinion, but no solid fact to back them up.



Electrical conductivity of Platinum: 94.34 1/mohm-cm

Electrical conductivity of Iridium: 188.679 1/mohm-cm

Electrical conductivity of Copper: 595.8 1/mohm-cm



Copper is the most conductive metal next to silver. If you are into power, spark energy, or conductivity, and heat transfer are two critical features to make peak HP. Copper conducts electricity and heat over 5 times better than platinum and almost 3 times better than iridium, but does not have the life span of either. Do you really need to get 100,000 miles out of a set of spark plugs? Would you really want to leave plugs in a motor for that long anyway? I wont pretend to speak for anyone else, but I think you know what my answer would be.



Copper corrodes faster than PL or IR, so they would require more maintenance. This is not an issue for me as I replace them often, but the average US car owner is very negligent when it comes to maintenance. This is partially the reason why some cars come from the factory with PL or IR plugs IMO.



I would never clean plugs because if I am going to spend the time to pull `em (15 minutes), I might as well drop in new ones. $8 a year (I pay $2/ea) you and have damn near perfect plugs. $16 a year and you would have perfect plugs.



If you are running a stock motor, copper is the way to go IMO.



Expensive spark plugs do not increase your vehicles performance and power.

Regular replacement does.



New plugs will only free up whatever power you lost due to running plugs too long. They do not and can not free up power that is not already there. While using a premium platinum plug will extend the service life of the plug, it will not in any way increase performance or power either, unless your plugs were holding you back for whatever reason to begin with.



The only realistic advantage of any premium plug is a decrease in gap erosion. Gap erosion occurs when the spark burns away small bits of the electrode and ground contact during combustion. Over time a properly gapped plug will slightly increase its gap but not generally enough to cause any problems if the plugs are replaced in accordance with the manufacturers suggested maintenance routine. So the extra dollars you pay for these kinds of plugs are truly wasted if you are a responsible vehicle owner who changes the plugs regularly like you should.



Keep your engine and your wallet happy by installing properly gapped, stock or quality replacement spark plugs at the required intervals.



Your choice of plug will depend on how often you want to replace them.



I run NGK copper exclusively. Since I put in new ones yearly, I have no need for iridium or platnium as they are for longevity only and do not increase horsepower or MPG regardless of what sooo many others want to believe. IMO, those who say otherwise are just trying to justify the extra money they spent on fancier plugs.



If any of you are REALLY interested in documented and independent testing data, and you have $14 to spare, go to the SAE site and order paper number 2006-01-0224, `The Effect of Sparkplug Design on Initial Flame Kernel Development and Sparkplug Performance`.

[paul34]

If you have no pressing special needs (such as running some sort of dedicated, unstreetable drag car or such), then get some iridium plugs, preferably Denso. There`s a reason many OEMs use Denso iridium on their motors from the factory - its tough to beat them for durability, and dependable performance spark after spark.

[Mopar]

If your car doesn`t run PLATINUM plugs from the factory DO NOT use them. I know we are talking Iridium and you should be fine with those.

[imported_Yal]

Check your factory manual and run the plugs it mentions.

[imported_Gears]

On the new Subarus the Turbos get Iridium and the regular engines call for Platinum.

[spike_africa]

Like he said dont waste your money on the hype a plug isnt going to make you faster. I run cheap NGK`s in my sprayed mustang.

[miahman98]

I would recommend you get a good set of wires instead expensive plugs. A good quality and well made set of wires will help keep you car running tip top for years to come. Go with the middle of the road plugs just so you don’t have to question your decision later.

[ofl0926]

On the new Subarus the Turbos get Iridium and the regular engines call for Platinum.

+1... remember that plugs and wires will produce an even spark and good combustion

[longdx]

Agreed that many "performance" claims of many plugs are just hype. I would recommend using the factory replacement plugs suitable for your application. A good rule of thumb, is to use Japanese specific plugs for imports, and American (Autolight, Motorcraft, etc) for domestics. Remember, Iridium helps in preventing corrosion at the tip and extends usable life of the plug (over 35k normal driving) whereas copper will corrode quicker but will still last @30k mileage.



I made the mistake of putting NKG iridium plugs in a domestic application , and the vehicle experienced driveability problems and threw some codes. Replaced with autolights (cheap factory OEM replacements) and all the problems went away.

[stiffdogg06]

Agreed that many "performance" claims of many plugs are just hype. I would recommend using the factory replacement plugs suitable for your application. A good rule of thumb, is to use Japanese specific plugs for imports, and American (Autolight, Motorcraft, etc) for domestics. Remember, Iridium helps in preventing corrosion at the tip and extends usable life of the plug (over 35k normal driving) whereas copper will corrode quicker but will still last @30k mileage.



I made the mistake of putting NKG iridium plugs in a domestic application , and the vehicle experienced driveability problems and threw some codes. Replaced with autolights (cheap factory OEM replacements) and all the problems went away.

I use NGK BRK7E gapped at .33" in my turboed civic.



I also suggest using what ever plugs your manual requires. They wouldn`t put them in the car from the factory if they weren`t made to run for a while.

[porcupine73]

For Subaru I would stick with ngk plugs. Even the ngk copper plugs give fine performance; the higher price plugs give longer life at least. If you replace wires (I`m assuming you have the n/a 2.5L; some other engines have coil on plug) , stick with OEM Subaru wires from a dealer (ie dealers selling parts online are usually much less expensive than walking ot a local dealer). Or magnecor wires; soobs sometimes misfire on parts store wires.



If you go platinum plugs for subaru you should use double platinum. Soobs use a waste spark setup that cna cause weird wear on single platinums (the polarity is reverse on the opposite cylinder).



The deep well spark plug socket i.e. this one from harbor frieght is excellent for the soobs fairly deeply recessed plugs





Also if you notice excessive oil in the spark plugs tubes, your spark plug tubes seals behind the valve covers need to be relpaced. Too much oil in the tubes can cause misfire.

[KnuckleBuckett]

I used to work in a facility that tested plugs for durability and performance. Bosch and NGK were always standouts.

[Setec Astronomy]

I used to work in a facility that tested plugs for durability and performance. Bosch and NGK were always standouts.

How long ago was this? I find the chain-store Bosch to be junk (although I haven`t used them in a long time because of a bad experience). Sometimes you get what you pay for...when Bosch first came out with "platinum" plugs they were selling them at pretty much the same price as a junk plug ($1 ea.)...but I said to myself "they can`t be junk; they`re platinum"...I was wrong...they were junk.