Does Log Dyno need an OBD Adapter?
No, you don’t need any sort of live connection, you only need a CSV datalog that contains RPM, or Speed from a GPS datalogger (this way RPM is calculated back from speed)
Is Log Dyno accurate?
Log Dyno is 100% accurate if you input the car details correctly. Also if you datalog has wheelspin or bumps in it, it might cause spikes in the RPM curve, which also causes spikes in the measurement curve, which invalidates the measurement, because peak numbers could be effected.