When increasing Miata power above factory levels, consider if you need new spark plugs. The heat range of your spark plug plays a huge role in the success and well being of your engine. Incorrect spark plug heat ranges can cause fouling, pre-ignition or detonation that can quickly ruin an engine. Gapping will play a large role in preventing the spark plug from blowing out under high boost conditions.
Additional Information:
- Miata Turbo Thread: What Spark Plug Should I Use?
- NGK Tech: Spark Plug Heat Range
- NGK Tech: Spark Plug Heat Range and Humidity
For most Miata's making over 170 hp, a commonly selected plug is the NGK- 4644 (BKR7E). In this example, the numeric value "7" refers to the heat range of the particular NGK spark plug line. Higher numeric values indicate colder NGK plugs. If using other plug brands this may differ - confirm which numeric direction (up or down) refers to a colder plug. These are typically gapped at .025" for stock coils and anywhere from .030-.050 for aftermarket coils (typical Toyota cops .032-.035").
