Car Diagnostics
Track day telemetry

OBD logging for track day: capturing engine data on track and what to do with the log

What to log on track via OBD-II (RPM, boost, oil temp, EGT, coolant), what rate (1 Hz vs 10 Hz), how not to lose data in corners, how to export into RaceRender / Trackaddict.

AI-generated 3 min read

Track day — a strong test for the car. OBD logging helps understand why power drops on lap 3, why oil overheats in fast corners, why LTFT drifts at WOT. Below: what to log, how, and how to analyse after.

What to log on track

Mandatory PIDs (10)

  1. RPM — baseline, normalisation
  2. Vehicle speed
  3. Coolant temp — critical at 220°F+, stop at 240°F+
  4. Oil temp (where available) — critical at 265°F+
  5. Boost pressure (turbo) — overboost control
  6. Air-fuel ratio (LTFT/STFT or wideband if fitted)
  7. Throttle position (%) — when WOT
  8. Fuel level (%) — for consumption calc
  9. EGT (where available) — critical at 1560°F+
  10. G-forces (from phone IMU) — separate channel, sync with OBD

Optional for advanced

  • Ignition timing advance (for detonation analysis)
  • MAP / MAF — for virtual dyno post-analysis
  • Individual O2 sensors (bank 1 sensor 1 / bank 2 sensor 1)

Logging frequency

  • 1 Hz — norm for 20+ min session (little data, easy analysis)
  • 5 Hz — sweet spot for most tracks
  • 10 Hz — for short events (braking, WOT, downshift)
  • 20 Hz+ — only with wideband + direct CAN logger (OBD-II can’t sustain)

ELM327 limit: ~10-25 commands/sec (see WiFi vs BT vs BLE post). So realistically 5-10 Hz on 3-4 PIDs simultaneously.

How not to lose data

  • Live sync to cloud — not an option until there’s LTE at the track (most tracks = dead zone)
  • Local buffer 500 MB+ — Car Diagnostics stores locally, syncs after session
  • Second phone as backup — in case the primary drops
  • Don’t leave phone on dash in sun — thermal throttling → data loss

Export formats

  • CSV — universal, for Excel/pandas/Python analysis
  • RaceRender 3 ($30) — overlay telemetry on GoPro video
  • Trackaddict — mobile app for lap analysis
  • AiM Sports RaceStudio — pro
  • VBOX Test Suite — for result validation

Car Diagnostics exports CSV and RaceRender-JSON formats.

What to analyse after session

Sanity checks

  • ECT max per session (norm < 220°F)
  • Oil temp max (norm < 265°F)
  • EGT max for turbo (norm < 1525°F)
  • Boost overshoot events (P0234 → map correction)

Performance analysis

  • Time in throttle > 80% (% of session time)
  • Max RPM per lap
  • Downshift consistency (RPM catch on shift)
  • G-force peak per corner (from IMU)

Fuel and stability

  • LTFT drift over session (norm ±3% start to end; more → tune fuel)
  • Rate of fuel consumption per lap (L/100km on track is 3-5× street)

Turbo-specific

  • Watch overboost — on track compressor may overheat, wastegate can’t cope
  • Monitor intercooler efficiency — if MAP-inlet temp rises over session, air-to-air intercooler isn’t keeping up; only air-to-water helps on extended sessions
  • Boost soft cut — if ECU limits boost, you’ll see it in the log

Diesel-specific

  • DPF regeneration may start mid-session — fuel consumption jumps
  • EGT max for diesel 1380-1470°F
  • Common-rail pressure — drop > 50 bar under load = HP pump aging

What Car Diagnostics does

We have Track Mode on paid tier:

  • 10 Hz logging 4 PIDs + IMU
  • Auto lap detection (by speed + IMU)
  • Post-session summary: max temps, WOT %, boost events
  • Export to RaceRender + CSV
  • Prediction Agent analyses: “engine getting hot in laps 5+, cool-down needed”

Try on free tier — pair an ELM327 adapter. Basic logging 3 PIDs at 1 Hz — free. Track Mode — on paid.