There's the problem of pollution... You want the exhaust to stay as close to the ground as possible to minimize exhaust fumes at head level... I remember reading this a while back...
As you can see from above, the exhaust is already pulled into that low pressure behind the car... Which is probably why most OEMs don't bother with upward pointing exhaust tips. Most I can find as reasons for high mounted exhausts on exotics is to allow for flat floors and a proper rear diffuser back there rather than direct aero benefit.
The closest I can find to a validation for this idea is this:
http://robotpig.net/__automotive/duc...ici.php?page=3
Which suggests that modern sports bikes use seat-mounted exhausts to push out the wake and make the bike more aerodynamic... But this will likely have more of an effect at high engine speeds and throttle than off throttle...
No doubt, if you have enough exhaust, as in an F1 engine spinning at 15,000 rpm or a bajillion horsepower dragster (where upward pointing exhausts actually produce downforce) you can do a lot of stuff with it. But for economy, you generally want to produce as little exhaust as possible, anyway. I guess it'd be worth it to eke out a tiny bit more economy at higher speeds... But probably the bigger benefit would be the flat floor.
Today
Other popular topics in this forum...
