Hotter plugs
- Advances ignition timing, more responsive engine
- More power, especially at high RPM
- Typically used on small-block engines
- Can cause pre-ignition
Colder plugs
- Delays ignition timing, smoother power response
- Less power
- Typically used on big-block engines
Longer plugs
- Increases compression
- Advances ignition timing
- More power, especially at high RPM