Spark plugs and octane level question

[chris_2.5gt]

Hey guys, got two questions.

I looked up the ngk spark plugs for a 97 2.5 legacy and I was looking at both the double platinum and long life iridium. After looking all over the net and finding controversial, at best, results I was curious what you guys have personally experienced is better for our car?

The second question I have also results from a few disputes I have read...what octane level should we be running? Is 87 fine or should I be running higher?

Chris

[subie/legacy]

I have no experice with the plugs so no help there.
but 87 should be fine. I believe thats what it was tuned for from the factory. if your having alot of pinging, you might consider running 89.

[mike-tracy]

Hey guys, got two questions.

I looked up the ngk spark plugs for a 97 2.5 legacy and I was looking at both the double platinum and long life iridium. After looking all over the net and finding controversial, at best, results I was curious what you guys have personally experienced is better for our car?

The second question I have also results from a few disputes I have read...what octane level should we be running? Is 87 fine or should I be running higher?

Chris


The NGK's all run great on our cars, the Iridium and Platinum are not as conductive materials as copper, so you'd be gaining a longer plug life for less performance (but so small a difference vs copper that it's just about unmeasurable). I don't know about other brands with N/a Subarus, but the older Legacy Turbos almost always work much better on copper NGKs (better than bosh platinum Iridium quad whatevers even)

The 1997+ 2.5 Legacy was tuned for 87 octane. Only the 96 2.5 called for premium, but one merely needs to put a 97-99 DOHC ECU in, and it will run fine on 87.
If yours seems kind of sluggish, you should reset the ECU and let it relearn 87. My friend only puts 91 octane into his RS (with the same motor as yours) and it does feel less peppy with 87, because the ECU learned on higher octane.

[chris_2.5gt]

Wow...makes a lot of sense, I haven't reset the ecu yet. On these cars is it simply unpluging the ground for 5-10 minutes only or do you have to turn the key 10 times or press the brake pedal or something like that?

[subie/legacy]

Wow...makes a lot of sense, I haven't reset the ecu yet. On these cars is it simply unpluging the ground for 5-10 minutes only or do you have to turn the key 10 times or press the brake pedal or something like that?

unhook the neg. terminal for 15-20min and press the break once or twice to be sure all power is out of the system.
that should be right, if I'm wrong im sure someone will chime in and correct me.

[rougeben83]

NGK and Champion are the plugs that came from the factory depending one where yours was made (japan or indiana). Coopers are fine, they have to be replaced ever 15k miles though IIRC. The iridiums are 2x that but they cost like 4x more. Up to you whether its worth the cost. 87 octane is fine, its what your car was originally tuned for. It may run a little smoother with higher octane, but the reason to have high octane is to prevent pinging - something even relatively stock motors don't have an issue with unless there's an underlying mechanical problem. If your car isn't tuned to take advantage of the higher octane, I don't see the point in the extra cost.

[chris_2.5gt]

ok so from what I gather, 87 is fine.
For the plugs it doesn't matter if I use the double platinum or the long life iridium? They are both made by NGK so that is fine. The copper plugs, what are they called and does ngk make them? I didn't see any mention of copper on their site.

[rougeben83]

They're called V-powers or something, it should be in the description.

[chris_2.5gt]

ok I see the v-power spark plugs on the site but my question for you is, do you get what you pay for?
The v-power are under regular class and are 2.89$ and the iridium and double platinum are under premium class and are 12.06$. I realize the iridium and double platinum will last longer but how much longer? And power wise copper is better right, although negligable?

[rougeben83]

ok I see the v-power spark plugs on the site but my question for you is, do you get what you pay for?
The v-power are under regular class and are 2.89$ and the iridium and double platinum are under premium class and are 12.06$. I realize the iridium and double platinum will last longer but how much longer? And power wise copper is better right, although negligable?


NGK and Champion are the plugs that came from the factory depending one where yours was made (japan or indiana). Coopers are fine, they have to be replaced ever 15k miles though IIRC. The iridiums are 2x that but they cost like 4x more. Up to you whether its worth the cost. 87 octane is fine, its what your car was originally tuned for. It may run a little smoother with higher octane, but the reason to have high octane is to prevent pinging - something even relatively stock motors don't have an issue with unless there's an underlying mechanical problem. If your car isn't tuned to take advantage of the higher octane, I don't see the point in the extra cost.

:smile:

The fact that youre replacing your old plugs with new ones will be the major performance difference that you will notice. You just don't have to do it as often with the iridiums or plats.

[wrxya33]

[quote="chris_2.5gt":1e8x63rx]Wow...makes a lot of sense, I haven't reset the ecu yet. On these cars is it simply unpluging the ground for 5-10 minutes only or do you have to turn the key 10 times or press the brake pedal or something like that?

unhook the neg. terminal for 15-20min and press the break once or twice to be sure all power is out of the system.
that should be right, if I'm wrong im sure someone will chime in and correct me.[/quote:1e8x63rx]

No need at all to wait more then a few seconds. Just unhook the neg terminal and step on your brake pedal for a few seconds, say 5 to be safe. Your power brakes will drain all the power from your cars electrical system and your ecu will be reset. I have done this method so many times works great for clearing CEL's too.

[ouch1011]

Just so you guys know, the learned ignition timing adjustments are not "resetable." If the PCM makes an adjustment to the ignition timing tables based off feedback from the knock sensor, it is perminent. I can supply the TSB from Subaru stating this if necessary. So, resetting the PCM will reset your fuel trims, but not the ignition trims.

For the spark plugs...my personal theory for my own car is that I don't want to leave spark plugs in aluminum heads for very long, mainly because the longer they stay in, the less likely they are to come out without damaging the threads. All it takes is some carbon built up on the end of the plug to damage the threads. So, I use copper plugs unless the car came with something else from the factory (like the Iridiums my Mazdaspeed3 came with, I replaced them with NGK Iridiums). Copper plugs last 30k miles in modern engines, thats a couple years for most people. Platinum plugs generally last 60k or so, double platinum and Iridium plugs can last up to 100k but again, I'm weary of running plugs for that long.

[Grafton]

I only got about the normal 15k on my ngk's
as for octane the current thinking is, like the ecu's on the turbo cars that constantly adjust timing, our cars do this but to a much smaller extent ie that the timing changes based on a more knock resistant fuel will only allow 3-6hp more than running regular in our cars

[anothernord]

Another thing to add is to ALWAYS use anti-seize when you put plugs in. If you don't you risk damaging the heads like someone mentioned.

[ouch1011]

I should also mention that the life mileage of your spark plugs will vary greatly depending on how you drive.

[chris_2.5gt]

I think all in all copper seems to be the best bet...strange, always figured to go with the most expensive for something like that.

[anothernord]

I think all in all copper seems to be the best bet...strange, always figured to go with the most expensive for something like that.

Yep. Copper is the best conductor of all the metals in the periodic table, and that's all it comes down to, besides longevity.