lethaldose

Ok this is something we all have to do at some point me personally i will do it atleast once if not twice a year. Changing plugs has been covered in several great DIY's and i will toss the links up for those. But not a whole lot is said about the selection of different heat ranges, copper v. platnium, etc... So that is what i wanted to cover and put the info i've came across out there for the fine folks that may be interested


DIYS:

http://www.scoobymods.com/spark_plug...42.html?t=4142

http://www.scoobymods.com/spark_plug...17.html?t=3017

So let's get this show on the road shall we!

HEAT RANGE

You hear it alot when you are shopping for plugs for a performance engine of some sort. Basically what it boils down to is the ability of a certain spark plug to wick away the excess heat of combustion.



What you want is just the right about of heat to give a nice even efficent burn, but not so much that you cause detonation/pre-ignition.

"When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter."



Now heat ranges vary the numbers for NGK are not the same as the numbers for Autolite. As an example the higher the number of NGK plugs the colder the plug, where as the higher the number in Autolite plugs the hotter the plug will be. So do your homework before snatching up your set.



A rule of thumb is for every 50-75HP extra you make over stock you should go a level colder with your spark plugs. This is very general and is only meant to give you an idea of what your looking for, because every engine and engine set


MATERIAL

You think a 12 dollar spark plug can conduct better than a 2 dollar spark plug?? Not so fast Charlie Brown lets talk about metals and how they relate to spark plugs.

The main materials you will run into are

Iridium

Iridium is a precious metal that is 6 times harder and 8 times stronger than platinum, it has a 1,200 degree (F) higher melting point than platinum and conducts electricity better. This makes it possible to create the finest wire center electrode ever

Platinum

Nearly all spark plug manufacturers use platinum in one form or another on their long life or performance spark plugs. This is because of platinum’s high melting point, which makes it useful in two ways. On long life spark plugs a thin wafer of platinum is bonded at the firing point to the center electrode solely so they don’t wear as fast as a traditional plug.

Copper

This is the old stand-by its cheap, very effective but isn't as durable as the most expensive counterparts. It also has a lower melting point (1000 degrees F) and is softer which equals to a quicker break down with use.

As far as being an efficient conductor Copper is the second highest metal element conductor right behind Silver.



Here are the Electrical Resistivity Ratings for these 3 metals
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge

Copper" @(20 °C) = 16.78 nΩ·m
Iridium: @(20 °C) = 47.1 nΩ·m
Platinum: @(20 °C) = 105 nΩ·m



Here are the most commonly recommended spark plugs you will likely encounter on your search. These are all STOCK heat range.

2002-2005 WRX

NGK IX iridium BKR6EIX
NGK Double Platinum PFR6G
NGk Platnium BKR6EGP
NGK Vpower Copper BKR6E

Autolite Extreme Sport XS3923DP (Iridium)
Autolite Extreme Performance XP3923 (double platinum)
Autolite Platinum AP3923
Autolite Copper 3923

Denso Iridium IK20
Denso Double Platinum PK20PR-P8
Denso Copper K20PR-U

Champion Iridium 9001
Champion Double Platinum RC10PYP4
Champion Platinum 3346
Champion Copper RC10YC4

Pulstar Pulse Plug BE-1

E3 E3 Spark Plug E3.64


2004-2009 WRX STI

NGK Laser Iridium Long Life ILFR6B

Autolite Xtreme Performance Iridium XP5325
Autolite Double Platinum APP5325

Champion Double Platinum 7975
Champion Copper REC10YC4


Denso Iridium Long Life SK20HR11
Denso Iridium IKH20
Denso Copper K20HR-U11

E3 E3.68

Pulstar Pulse Plug DG-1



2006-2009 WRX

NGK Laser Iridium Long Life ILFR6B
Autolite Xtreme Performance Iridium XP5325
Autolite Double Platinum APP5325

Champion Double Platinum 7975
Champion Copper REC10YC4


Denso Iridium Long Life SK20HR11
Denso Iridium IKH20
Denso Copper K20HR-U11

E3 E3.68

Pulstar Pulse Plug DG-1



Heat Range Chart




My own take on all this is personally I've had better luck out of Autolite 3922 (one stage colder) copper plugs in my Stage 2 WRX. These are under 2 bucks each so they are cheap to replace and i will normal go through 2 sets a year. But from a tuning stand point i noticed a reduction in knock and the ability to add more timing through out the tables compared to my 7 heat range Iridium NGK's that were 8 dollars each.

But the real truth is you will have to make the choice yourself and find one that is right for you. I just hope I've provided some ammo for you to hunt down the right plug.

Further Reading

http://www.carcraft.com/howto/116_07...eat_range.html

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spending money I don't have, to buy parts I don't need, to impress people I don't know

 

c0mpl3x

the correct way to read plugs is to cut away the threads

lethaldose

this isn't about reading them its about picking a style/heat range. although you can get an idea of the heat range of a plug by chopping them up.... BUT its much easier to just cross ref the PN imo

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spending money I don't have, to buy parts I don't need, to impress people I don't know

c0mpl3x

reading plugs = choosing the heat range. you don't just assume you can drop two steps or raise one step, you go by what the plugs read to choose the heat range whether or not your engine likes that specific range

http://www.dragstuff.com/techarticle...ark-plugs.html

lethaldose

http://www.carcraft.com/howto/116_07...eat_range.html

actually gives info on doing a cut away etc....

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spending money I don't have, to buy parts I don't need, to impress people I don't know

narcispy

personally.. i dislike autolite plugs, ngk just seem better for japanese engines, imo

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You just beat another wagon!

lethaldose

The reason i went with autolites was availability in my area, all NGK's weren't an "in stock" plug for some gay reason. So i was in a hurry and grabbed the Autolites, they've done so well for me i've just not swapped to an NGK.

I have no complaints about Autolite, Bosch, or NGK but i refuse to put a Champion plug in anything haha

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spending money I don't have, to buy parts I don't need, to impress people I don't know

narcispy

I always used ngks in my mazda's and I swore by them and it was normally the only thing the parts store had in stock. Yeah champions suck the only thing I use them in is the lawn mower

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You just beat another wagon!

lethaldose

i don't even do that to my lawn mower LOL

__________________
spending money I don't have, to buy parts I don't need, to impress people I don't know