Reading a dyno sheet and log

A power curve is torque times rpm. The log is where the reasons live.

Wheel power is wheel torque × rpm ÷ a constant. The torque curve shows where the engine breathes best; the power curve is that multiplied by speed, so power keeps rising after torque peaks until torque falls faster than rpm climbs. Peak numbers sell cars; the shape of the curve and what happened under it sell tunes.

Sweep vs steady-state

• A sweep (ramp pull) holds a start rpm, then lets the engine accelerate against a controlled ramp. It covers the full-load row of every table in one pass and produces the power curve.
• Steady-state holds one rpm and throttle so you can tune a single cell and watch the response. It is slower and hotter, and it is how part-throttle cells get tuned properly.

Reading a log

• Start with the mixture: λ target (table), λ final (after protection) and λ measured. Remember the wideband reads ~150 ms late.
• Then ignition: table, trims, knock retard, final. Any retard means the map was past the limit there.
• Then the knock level against the threshold, injector duty, fuel pressure, EGT.
• Scrub the log and watch which table cell the engine was in; select cells and see when they were active.