eggs · 12 min read · easy
Dyno Testing 101: Reading Your Sheet Like a Tuner
A dyno chart sells a tune more than any sales pitch. It also lies more than any sales pitch. Here is how to read one honestly.
Hub, Roller, Engine Dynos
Engine dyno (EDC): measures at the crankshaft, no drivetrain losses. Roller dyno (Dynojet, Mustang): measures at wheels, multiplies by 1.15-1.25 for AWD or 1.10-1.15 for FWD/RWD. Hub dyno (Mainline DynoLog, Rototest): measures at the hub, eliminates tire slip — most repeatable.
Why Two Dynos Disagree
Correction factor (SAE, DIN, STD, JIS — each adds or subtracts ~3%). Strap tension (more downforce = more reading on inertia dynos). Tire pressure (low PSI inflates reading). Loading mode (sweep vs step). Ambient temperature/humidity. Two clean shops can be 15+ hp apart on the same car.
Reading the Plot
Look for: smooth torque curve (no jagged spikes — those are knock or fuel cuts). Boost curve plateau (if it climbs without plateau, your wastegate is creeping). AFR/lambda curve at WOT (must be 11.5-12.5:1 on petrol turbo, smooth). EGT below 950C on petrol, 750C on diesel. Knock counter: zero across the whole pull.
Spotting Dishonest Plots
No baseline run shown. Y-axis truncated to exaggerate gains. Smoothed curves hiding fuel cuts. Single peak number without RPM range. Comparison plot from a different car. No date/temperature on header.
Same-Day Before/After
A reputable shop will baseline your car BEFORE flashing, then re-pull immediately after, on the same dyno, with same straps, fuel, and ambient — within minutes. Anything else is comparing different days, and that means different ambient correction.
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