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AMBIVALENCE 03-31-2006 04:45 PM

Spark Plug
I own a 2006 2.5i, and i was thinking of swaping into some better performance spark plug. but i have a few question unanswered, hopefully someone can help me. :icon_mad:

1. What spark plug should i change into for a 2.5i model? (Brand and model?) And how much HP increase would i get?
2. Does changing to new spark plug increase fuel consumption?

(I dont see anyone that brought up this topic in the search. but if someone can gimme some old post that already mention similar info that would be helpful as well. THX!)

trohler 03-31-2006 05:12 PM

I believe the factory plugs are either platinum or iridum (sp?) so there is probably no need or benefit to changing them out before they are bad or reccomended replacement interval.


robsontuning 04-01-2006 02:42 PM

I think only the STi has the Iridium plugs and the rest are platnum. Not 100% sure, but I know the WRX is platnum and the STI is Iridium

GTsleeper 04-01-2006 04:18 PM

i believe we (LGT) have Iridium also.

subatwo 04-01-2006 05:18 PM

according to the subaru website the plugs for the 2.5i are platinum. GT's get the Iridium plug

pillboy 04-01-2006 08:19 PM

To answer your questions:

1) Use what the manufacturer recommends...are you smarter than them? I know I'm not. All the spark is doing is igniting the fuel/air are you going to get more HP from a different spark?

2) I am sure someone will disagee with me, but I don't see how this is possible. Same amount of fuel is making its way into the combustion chamber regardless of what spark plug you have screwed into the hole. I could maybe see a decrease in fuel efficiency if you were to put in a radically incorrect spark plug that caused the engine to run poorly.

If you are looking for a relatively inexpensive way to gain a few HP by replacing the plugs, I think you are searching in vain.

mccorry 04-01-2006 08:42 PM


Just to verify... the i's use Platinum... the GT's use Iridium.

Spark plugs will not make more (significant) HP
Replacing severly worn spark plugs can increase milage.

MDTURBO 04-01-2006 09:26 PM

Stock Heat Range

One Step Colder Heat Range

AMBIVALENCE 04-01-2006 10:46 PM

Thx guys for answering my question!
Damn i always thought spark plug could increase HPs...

Well. i guess i really dun need that much HP anyways, i am more towards gas-saving solutions. maybe i'll post another post by then =)

robinlsb 04-02-2006 04:41 AM

+1 for pillboy, Also proper gap is important. A colder plug will help per-ignition of a very hot motor(usually in racing). The disadvantage of colder plugs is that they can foul (missfire) at lower temps thus reducing performance.

GTsleeper 04-02-2006 09:48 AM

^^^ thats why u dont step down till ur after stage 2

AMBIVALENCE 04-02-2006 11:54 AM

yes i gotta thx pillboy's info. that made me understand that spark plug does not equal to performance, i was wrong for several years.
Or... was it just for legacy? =)

robinlsb 04-02-2006 01:55 PM

all engines

johnAWD 04-02-2006 02:28 PM

Spark plugs can't increase power, but they can fend of detonation if you are on the edge. That would have the net effect of 'giving back' power that you've lost due to running too hot.

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