Does a Stage 1 remap actually improve fuel economy? The honest answer: it can — but it depends entirely on how you drive afterwards.
Diesel Stage 1 MPG gains
Modern common-rail diesels typically see 3–8 MPG improvement on motorway cruising with a Stage 1 map. The reason: more low-down torque means the engine spends more time in a more efficient part of the rev range.
Petrol Stage 1 MPG gains
Turbocharged petrols see smaller gains — typically 1–3 MPG on a steady cruise — because the gains are mostly in the boosted upper rev range, which you don't use cruising.
The catch
If you use the extra power, your MPG goes down — physics doesn't lie. The MPG gain only appears if you drive identically to before but let the engine work less hard for the same speed.
Our recommendation
If your priority is fuel economy, ask for an 'eco map' — a Stage 1 file tuned specifically for torque-rich low-rev efficiency rather than peak power.
Related services on StageMyCar: Stage 1 remap and car remapping in Hounslow.