With a performance machine like the Focus ST, or the Focus RS, you should change your plugs every so often to ensure you are getting the best performance.
Also, any time you increase the boost you should replace the spark plugs with better plugs that can tolerate more heat.
We refer to the spark plug operating range as the heat range. When you are running more boost, you should get one range colder plugs.
For you Focus ST and RS owners looking for one range colder NGK Iridium plugs, you are in luck, we have them in stock!
Click on the photo to jump to our product page for more info.