I've been playing around with my OBD datalogger and thought I'd share the spreadsheet that I've been using to calculate SAE and drag corrected hp/tq curves.

Inputs include:
1. logged OBD rpm data
2. OBD log interval
3. gear ratios
4. tire dimensions
5. vehicle weight
6. frontal area
7. drag coefficient
8. ambient air pressure, temp and dew point which can be gotten from http://www.weather.com.