Set of Ford Performance Cold Spark Plugs for the 2013, 2014, 2015, 2016 and 2017 Focus ST and 2016-2017 Focus RS.
When upgrading your 2013-2017 Focus ST or 2016-2017 Focus RS with more modifications it may become necessary to upgrade the spark plugs as well. As the cylinder combustion pressures increase, a colder spark plug may be required. This means adding more boost will require colder spark plugs.
The spark plugs in this set are two heat ranges colder than the stock EcoBoost engine spark plugs. They are the same spark plugs that are included with the Ford Performance Calibration Kit (M-9603A-FST).
Sold as a set of four spark plugs. They come pre-gapped to 0.028-inch (0.71mm).
A colder spark plug does not mean the spark plug uses less voltage or produces less electrical energy. The heat range of a spark plug is the range in which the spark plug works well thermally. The main difference that affects the heat range is the length of the insulator nose. A hotter spark plug has a longer insulator nose and a colder plug has a shorter insulator nose. A longer insulator nose means the path for heat dissipation from the insulator nose to the cylinder heat is longer and the firing end stays hotter. Also, more surface area is exposed to the ignited gases so the spark plug is easily heated to higher temperatures. A colder spark plug functions in the opposite manner.
Using spark plugs with too hot of a heat range may result in detonation. If too cool of a heat range is used, the spark plugs may foul.
