Mister Quickie

I run my pickup without it (I know different vehicle) with no issues. These underneath jobs on the 2005 Cayenne would be much faster without having to take off and replace the engine splash guard but I know on the Audis you have to keep them on

Libast

Probably not but then again, my time valuation is different than you- the extra 5 min of taking down the splash shield is worth the x-hundred time in replacing part of the engine due to a random piece of gravel.

thesteve

+1 on hating to remove that plastic. Especially with those two screws on either end that attach high up out of reach.
I would think the biggest effect would be aerodynamics and maybe fuel economy as a result but I'm just guessing.

Andrew_955

The undertray is to assist with cooling. By having the front section of the engine bay fairly sealed off and an open section at the back it means that all incoming air must be pulled through the radiator. By removing the undertray you allow turbulent air to enter the front of the engine bay from underneath, spoiling the venturi effect and bypassing the radiator.
Same principle as fan shrouds but on a bigger scale.

Most cars will run just fine without the undertray, but some will overheat in certain airflow conditions.

TomF

^^THIS^^ I for one hate replaciing the undertrays (and I have the stamped steel engine guard) but it is worth it for the cooling effects as well as to keep the components clean. With 630+HP, the turbos generate a ton of heat...