Spark Plug info for your Subaru WRX/STi:

So how do colder plugs actually remove heat?

Spark plug comparison hot vs colder plug.
Spark plug comparison hot vs colder plug.
How do I troubleshoot my spark plugs upon removal to diagnose problems?
a. .pdf document by Autolite
b. .pdf document by Bosch
c. html page by Denso

What is the #1 spark plug fault? Improper torque when installing them. If you under torque a plug, you could destroy your engine due to reduced heat transfer at the threads, thus causing the plug to overheat and pre-ignite. This is actually common due to the gasket making the plug feel tight when its not. Use a torque wrench each and every time! There are other methods to do this, but they should only be used in an emergency or by people who have a sense of feel and experience.What is the torque specification on spark plugs? 15-19 ft-lbs. If a torque wrench is not available, tighten hand tight. Then tighten with a standard socket wrench and additional 1/4 to 1/2 of a turn. And for you super anal retentive and smart folks, when using anti-seize compound on spark plugs, you can effectively reduce the torque needed by 1/3, but at these low torque levels it’s really not going to matter.