Why the dyno isn't the finish line
The dyno is great for wide-open throttle and steady loads. Real driving adds cold starts, light-throttle cruising, slow traffic and long downhill runs. After the dyno session, it's normal to spend time on the road smoothing the parts of the map you use every day. The goals don't change from engine to engine. It's all about getting the right mixture for each kind of load.
Mixture targets by load
| Condition | Mixture | Why |
|---|---|---|
| Full load, naturally aspirated | Around 12.5:1 to 13.5:1 AFR | Richer than stoichiometric for power and a safety margin |
| Full load, turbo or supercharged | No leaner than about 12.5:1, and as rich as 10.5:1 | Extra fuel cools the combustion chamber |
| Cruise, light to medium load | As close to stoichiometric as possible | Best economy and clean running |
| Deceleration | Can be run lean | Saves fuel when little power is needed |
At full load, every engine should be richer than stoichiometric at every RPM. Boosted engines deserve special attention. They may make a little more power on the lean side, but the extra combustion heat is what damages pistons, valves and turbos. That trade isn't worth it on a car that has to live.
Read the shape of the map
Follow those rules and the fuel map takes on a recognizable shape: rich across the high-load area, close to stoich through cruise, leaner in the light-load corners. Just as important, it should be smooth. Airflow changes gradually with RPM and load, so the table should too. A cell that sticks up or dips sharply compared with its neighbors is almost always a mistake, often a one-off correction from a single bad log. Smooth it out and retest.
How we fine-tune on the road
- Log with the wideband across normal driving: cold start, cruise, gentle and firm acceleration, and decel.
- Correct cruise cells toward stoich first, since that's where the car spends most of its time.
- Check transitions between areas and smooth any steps.
- Only then let closed loop trims handle small day-to-day changes.
Related reading: tuning the base tables, applying load to the engine and the QuickTune feature.
