What should the air-fuel ratio be for a Mazda RX-7 FD?

For a turbocharged Mazda RX-7 FD, the ideal air-fuel ratio (AFR) depends heavily on whether the engine is idling, cruising, or under boost. Because rotary engines are extremely sensitive to running lean under load, hitting these fuel targets is critical for reliability.

Here are the recommended AFR targets for your FD:

• Idle: Aim for 12.5:1 to 13.5:1 for a strong, stable idle. You should generally avoid going leaner than 14.0:1 at idle ⁵.
• Cruising (In Vacuum): You can safely run around 14.0:1 during normal cruising. At speeds above 40 mph, you can often lean it out further to around 16.0:1, provided the engine runs smoothly and the car doesn't buck ⁵.
• Low to Medium Boost (5 to 10 psi): Target 11.2:1 to 11.5:1 on the dyno. Under real-world road conditions, the extra load will naturally lean this out slightly to around 12.0:1, which is a great target for this boost level ².
• High Boost (10+ psi / WOT): As boost rises, you must add more fuel. Target 10.5:1 to 11.2:1. Tuning for 10.5:1 under high boost provides a vital safety margin to protect the engine against hot ambient temperatures or poor-quality pump gas ².

Safety Warning: Never allow your AFR to reach 13.0:1 or leaner while under boost. Running lean under pressure on a turbocharged rotary will quickly result in severe engine damage or blown apex seals ².

Difficulty Rating: Expert Tuning a rotary fuel map requires a high level of expertise. Always ensure you are using an accurate, high-quality wideband O2 sensor to monitor and log your air-fuel ratios while making adjustments.