The Vertical Aspirations of Soot
An internal combustion engine breathes. It draws in oxygen, mixes it with the volatile remains of the Carboniferous period, and pushes the byproduct out through a run of pipes. On most cars that exhalation points at the asphalt, dumping its waste near the curb. Tilt the tailpipe skyward and the machine starts making a different kind of claim.
The upward stack—standard on heavy diesel rigs, occasional on the idiosyncratic sedan—inverts the usual modesty of the exhaust system, and it has a pedigree. On the steamships and locomotives of the nineteenth century, the funnel lifted scorching gases and embers well above the passengers and clear of the era's flammable timber. To point a pipe at the clouds is to borrow that look: a machine loud enough that its breath had better be vented overhead rather than into the gutter.
The direction is not purely theatrical. Engineers have to reckon with backpressure, the resistance exhaust gases meet as they thread the manifold and the catalytic converter. A good system works as a scavenger, using pressure waves to draw the next charge of air into the cylinders more efficiently. Turned upward on a diesel, the pipe also lofts particulate matter and nitrogen oxides into the air above the road, in theory scattering the worst of the smell before it reaches the open windows of the car behind.
There is some honesty in the arrangement. A hidden tailpipe lets a car pretend it runs on magic; the vertical stack admits to the heat and chemistry it takes to shove a ton of steel down a highway. It is a chimney for a mobile hearth.