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Old 04-20-2008, 03:06 PM   #1
myquicksti
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Member#: 146902
Join Date: Apr 2007
Vehicle:
04 sti
silver

Default So which plug should i use?

So i read all the faq and unabomber stuff "great write up" but still unclear.62,000 miles stg2 accesport forunt mount catless 3" turbo back and recirc aps bov. Fuel pump and short ram 20 psi runs great for what it is .Started little rough idle in the morning just for a second or two and smoothes out. Just started happening this week . Its been on these mods for aprox 20k miles or so and still holds 20 psi when into it an aprox 19 to 20 inches of vacum @ idle. So i figured maybe thrugh a set of plugs @ it. but now due Istick to the stock plug or a step colder.Dont mine spending the money and even if be comes a more freqent thing like having to replace every 10k or 12k. to sacrifice a little more so be it. i would have pm unabomber but i dont have a paypal account. Thks for the help pics comming soon...
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Old 04-23-2008, 01:31 AM   #2
elusiv
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2002 WRX
PSM TXS Stage Eleventy

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Stock spec.
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Old 04-23-2008, 01:57 AM   #3
arch4life
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i believe the common rule of thumb is for every 100 hp gain, drop a step colder.

in reality you really wont notice a large change between a step colder plug and a normal plug, all else equal at idle.

do you have any tuning? is the car running proper afr's on boost? these are things to consider as improper afr's can cause lots of issues, one of them being fouled spark plugs.

i wouldnt quickly put the blame on the spark plugs, if that is all you've considered. lots of things can cause a rough idle, perhaps you just need to clean out your Idle air control valve.
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Old 04-23-2008, 01:11 PM   #4
jaxscuby
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WRB

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stock boost ~15 psi (14.7) for stock plugs
20 psi get the colder plug.
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Old 04-23-2008, 09:01 PM   #5
elusiv
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Quote:
Originally Posted by jaxscuby View Post
stock boost ~15 psi (14.7) for stock plugs
20 psi get the colder plug.
What does 20psi have to do with anything?
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