Jaguar XJ 4.2 V8 SC 400hp Remap

The Jaguar XJ 4.2 V8 SC 400hp is a 4.2L naturally aspirated petrol engine producing 400 BHP and 540 Nm from the factory. With a typical Stage 1 remap, output increases to approximately 470 BHP and 630 Nm — a gain of around 70 BHP (18%) and 90 Nm (17%).

This engine has limited remap suitability, with a balanced spread of gains across both power and torque — providing a noticeable improvement across the rev range. The tuning headroom is classified as moderate, based on the percentage gain available from the factory output.

From a technical perspective, the transmission is many variants use zf 8-speed automatic (where fitted). at this torque level, transmission and driveline servicing history becomes especially important..

Considerations: Naturally aspirated engine: gains are usually limited; results vary widely.. Unusually high gain for NA engine: treat as an estimate and verify against the exact engine variant.. High tuned torque: check transmission torque capacity and service history.

All figures shown are typical estimates based on aggregated Stage 1 data for this engine variant. Actual results depend on vehicle condition, mileage, and the chosen tuning method. We recommend discussing your specific vehicle with a qualified remap professional.