[kach22i]

Originally Posted by samwichse

Those big honking exhaust pipes are actually exhaust electors, basically venturis that act something like the "air multiplier" on those Dyson bladeless desk fans to suck air though the engine. Voila, an extra chunk of HP not used by the cooling system!

That's got to have some limitations, otherwise it's use would have been more widespread, right?

2013
Giving Your Fleet an Aerodynamic Advantage
https://www.fleetio.com/blog/giving-...amic-advantage

You can already see the widespread advancement of aerodynamics by major manufacturers. New models by Ford, GM, and Volvo are sporting thoughtfully designed features like front grill shutters, streamlined mirror covers and enhanced ground effects.

For tractor trailers, there are a number of add-ons that can make the rig slicker going down the road. These include side skirts, rear covers and fairings - all having the objective of keeping the air flow as laminar (non-turbulent) as possible. You will see a lot of focus on decreasing wheel exposure, as spinning air surrounding them creates a profile much larger frontal area than the tire size implies.