Dyno & Performance

Read your dyno like a pro. Make changes that matter.

Everything you need to prep, run, and interpret dyno sessions the DMS way — so your graphs tell the truth and your tune gets faster, safer, and smoother.

1) What a dyno actually measures

Power (hp/kW) and Torque (Nm) are derived from the dyno’s roller/brake load and engine speed. Your graph is a story of airflow, fuel, and timing under controlled conditions.

  • Power curve: How fast the engine does work (top-end breathing).
  • Torque curve: How strongly it twists (mid-range response).
  • AFR/Lambda: Combustion health under load.
  • Boost/MAP: Air mass and control stability.
  • IAT/ECT: Heat management and repeatability.

Key concept — repeatability

We care less about peak numbers and more about repeatable trends. If the setup repeats within a small margin across runs, we can trust changes in the tune or hardware.

2) Pre-dyno checklist

  • Fresh fuel (correct octane), no leaks, correct oil level.
  • Tire pressure set, wheel nuts torqued, no exposed threads/rubbing.
  • Intake/IC piping secured, clamps tight, vacuum lines intact.
  • Cooling system bled; radiator fans operational.
  • ECU has no critical DTCs; CEL concerns addressed.
  • Laptop + cable ready (logging works, power supply OK).
  • Battery on charger/stabilizer if flashing on site.
  • Baseline data ready (previous logs, mods list, tires/gear ratio).
  • Agree on run ranges (e.g., 2,500 → rev limit) and gear.

3) DMS dyno methodology

Setup & strapping

  • Strap at hub height, car centered, zero toe steer from straps.
  • Front/rear straps tensioned evenly; suspension settled.
  • Fans directed to radiator + intercooler; replicate road airflow.

Gear choice

Use the gear closest to 1:1 (MX-5 NC: typically 4th) unless speed limits dictate otherwise. Consistency beats ego-numbers.

Run procedure

  • Stabilize temp at cruise load; start logs (AFR, MAP, IAT, trims, knock).
  • Full sweep pull (e.g., 2,500 → 7,000 rpm) with steady throttle.
  • Cooldown to equalize IAT/ECT; repeat for validation.

We keep smoothing moderate and correction consistent across runs for fair comparisons.

4) Reading the graphs

Power/Torque behavior

  • Flat torque + rising power: Healthy turbo spool and top-end.
  • Torque dip mid-range: Timing pulled, boost control soft, or knock/IAT.
  • Power falls early: Backpressure, cam timing, or ignition ceiling.

AFR/Lambda

  • NA: typically ~12.8–13.0:1 at WOT; Turbo: ~11.5–12.0:1 (fuel & hardware dependent).
  • Wavy AFR: fuel system limits, MAF scaling, or O2 feedback boundaries.

Boost/MAP control

  • Clean rise → slight taper is normal; oscillation = duty/gain mismatch or leaks.
  • Early boost cut: check target vs limiters and solenoid polarity/duty cap.

Temps

  • Rising IAT shifts knock threshold; expect timing trims.
  • ECT creep = airflow/fan strategy or coolant issues; pause and cool.

5) Corrections, smoothing & comparability

Environmental correction

  • Use the same SAE/DIN correction across sessions.
  • Log ambient temp, pressure, humidity for transparency.

Smoothing

  • Low smoothing exposes noise; high smoothing hides issues.
  • Pick a middle value and keep it fixed when comparing.
Same gear Same strapping Same fan setup Same correction Same smoothing
→ apples to apples

6) Common issues & quick fixes

Oscillating boost

  • Lower gain or adjust duty ramp; verify plumbing and check valve orientation.
  • Wastegate preload too high/low → set baseline properly.

Fueling limits

  • High IDC/leaning out → injectors/pump limits or voltage drop.
  • MAF pegging → resize housing or switch to SD (where appropriate).

Heat soak

  • Extend cool-downs; improve fan angle/CFM; shield turbo hot side.
  • Compare first vs third pull to quantify soak effect.

Knock activity

  • Revisit timing, AFR, IAT; inspect plugs, fuel quality, and mechanical noise sources.

7) MX-5 NC specifics (quick notes)

  • 4th gear is typically closest to 1:1; confirm per diff/box.
  • Stock airbox vs open filter can change MAF behavior on the rollers.
  • Turbo NC: prioritize IC airflow (fan angle), not just radiator face.
  • Cam swaps: expect VE shifts — re-map MAF/SD and revisit spark maps.

8) A clean run plan to copy

Session: 5 pulls total
1) Baseline warm pull (2,500 → rev limit) — log AFR/MAP/IAT/ECT/knock
2) Repeat for validation (same settings)
3) Make change #1 (e.g., WG duty +5%) → single pull
4) Cooldown (IAT within +2–3°C of first pull) → validation pull
5) Make change #2 (e.g., +1° mid timing if knock-free) → validation pull
Keep correction/smoothing constant • Save graphs + raw logs • Note ambient

Save graph images and raw CSV logs for each stage. We prefer before/after overlays with identical axes limits.

9) Mini glossary

AFR / Lambda

Air-fuel ratio; Lambda = AFR ÷ 14.7 (for petrol). Use both for sanity checks.

IAT / ECT

Intake air / engine coolant temps; both shift knock limits and repeatability.

IDC

Injector duty cycle; sustained 95–100% indicates fueling headroom is gone.

10) FAQ

Do dyno numbers equal road performance?

Not always. Use the dyno for relative changes and shape, confirm on the road/track with real IAT/RAM effects.

Which smoothing value should I use?

Pick a middle value that doesn’t hide problems; keep it identical across comparisons.

How many pulls are enough?

Two matching baselines + one after each change, with cooldowns that keep IAT/ECT comparable.

Need help reading your graph? Send us your logs and dyno files — we’ll mark issues and next steps.
Ask Yiannis