Determining BSFC map from logged OBD2 data

[fumesucker]

I went ahead and bit the bullet and ordered an Elm327 interface for the OBD2 port.. I imagine it should be here in a week or so.

What I'm interested in (besides the obvious mpg data) is logging data that will allow me to derive a BSFC map, I think such a thing would be very helpful for those wanting to keep their engine running in the most efficient portion of its operating range.

It seems to me that BSFC could be determined from speed, injector width, throttle position and rpm signals with a little math. I'm still mulling over what would need to be done with the data but I think I have a handle on it.

Determine horsepower from acceleration and weight, then the BSFC for various rpm and throttle settings could be found by measuring injector pulse width to get fuel flow figures for each set of operating conditions.

Any thoughts?