You could, but I wonder if it would be as conclusive as real world testing? and You'd have to perform several sets of calculations.
1. Engine speed increases as vehicle speed does, until a gear change
2. Exhaust CFM/airflow changes with pedal modulation... (think: turbocharger)
3. Air mass over/around the vehicle obviously changes with vehicle speed, not to mention every time the wind blows...
There are too many variables, IMO, to answer a question like this with mathematics alone. At least not for someone like me, who isn't interested in sitting around crunching numbers to attempt to cover every possible variable/scenario. Someone else can take that liberty. LOL.
Real world testing may be in order, but most probably on a track. (Unless someone plans some serious vehicle modifications). But even modifying the vehicle to put the exhaust in the rear end's low pressure area would breed questions such as "would it help more at the top of the area or the bottom? either side?" etc and so on.
Speculatively, I can say that adding ANY amount of pressure to a low-pressure or vacuum area would reduce the amount of vacuum (increase overall pressure) and SHOULD help, even if marginally.
Less speculatively, I would wonder if the necessary modification would prove it's worth for the return on investment over a viable period of time.
Also, a question... if the exhaust were in the wake area, would that not create a vacuum and aid the scavenging cycle in the exhaust, since the area the exhaust is exiting into would obviously be a vacuum... thus "Drawing" the gasses out of the pipe.
It might be beneficial to performance in more than one way. Speculatively.
