Rotax MAX spark plug heat range chart for optimal performance

Choosing the right spark plug for your Rotax MAX 125 Senior Evo engine is critical to maximizing power, reliability, and throttle response. Whether you're racing in hot summer temps or tuning for a chilly morning session, this spark plug heat range guide will help you select the ideal plug. Below is a full spark plug temperature chart for Denso and NGK plugs—complete with usage tips, ideal ambient temperatures, and performance recommendations.

🧠 Quick Tips for Racers

• ✅ Use GR8DI-8 for most conditions. It's the factory-recommended Rotax MAX Challenge plug.

• ⚠️ Use IW31 only for cold ambient temps or warm-up sessions. Too hot for full race pace.

• 🌞 Use GR9DI-8 or IW27 for hot summer races, high RPM tracks, or long endurance runs to avoid pre-ignition.

🔍 Plug Color Reference (After a Session)

• Light tan: ✅ Ideal combustion

• White / blistered: 🔥 Too lean/hot — risk of detonation

• Black / sooty: ❄️ Too rich/cold — risk of fouling