I do most of my tuning on the street. It's as close as you can get to an unlimited Eddy-current type loading dyno for free. In my opinion, even considering non-inertial loading type dynos, there is still no better way to tune a car to run absolutely like an OEM vehicle then by street tuning. The only disadvantage of street tuning is that you can only really tune your fuel map. Tuning timing on the street is somewhat of a guess, along with tuning on an inertial dyno. On a Dynojet, at least you can see power increase/drops -- but that doesn't tell you the full story on timing. In a perfect world, I would start with general timing numbers that are known to work for that particular vehicle, and do all the fuel mapping on the street using a wideband and laptop or some other type of data-logger. When the fuel map is nailed, start looking for a dyno an Eddy-Curret loading type dyno that has a 4 gas exhaust analyzer. This exhaust analyzer (not wideband) is about as close as you will get to see if your timing is 'right'. Also note that changes in timing rarely, if at all, impact the fuel map. In my opinion, tune to a mint fuel map with standard/conservative timing on the street, then fine tuning the timing (maybe fuel) on a non-inertial dyno is the way to go.
As far as being possible to Map an ECU on an inertial dyno -- anything is possible, but your WOT and idle will be MUCH better then your closed loop and vacuum parts of the map. I drive my car on the street, and as far as map reliability and streetability, using a dynojet for anything other then checking WOT A/F or seeing the shape of your HP/TQ curve is a joke. You're really not going to be able to nail 'cruise' loads on an inertial.
