bumper vents

[lunarhighway]

would drilling a lot of small holes in the upper portion of my rear bumper help reduce drag?

i'd put them in the locations marked in red


the idea is based on the mercedes taillight vents that take air from underneath the car and vent it at the edge of the taillights to improve a clean airflow sepparation wich would not occur if the lights had no vents and where shaped as the are.

the main idea behind my proposal is that air curently being scooped up by the rear bumper would be vented trought the holes due to the pressure difference.

if nothing else this should increase the pressure behind the car, but perhaps also stabilise the airflow.

the holes near the edge of the bumper might help a little to improve sepparation there.
the holes would be in the unpained portion of the bumper so they'd be fairly invisible. larger holes with some incerts might even resemble parking sensors. right now the bumper doesn't fit very tight and looking from below you can actually see light between the bumper and the trunklid edge so perhaps air is already being vented trought there.

but could it work and produce a measurable difference or could it have potential downsides?

[Christ]

In a similar thread, I remember a post from Phil (Aerohead) mentioning that the area under your car isn't really acting as a parachute for air, rather dragging along a stagnant bubble, keeping actual flow away from parts inside the bubble.

The thread discussed the uses and potential benefits of "speed holes".

[Christ]

This post:

Originally Posted by aerohead

Ollie,imagine that the air captured within the boundary between both bumpers and the rocker panels just travels with the car.Like a pool of water upside down,with no influence from gravity.
If air WERE moving there,it would be like a literal torture-chamber for the air,with nothing but separated flow and mass quantities of turbulence.
By "capturing" air underneath there,all the air flowing below,will pass by undisturbed,with an un-obstructed path to the rear where it can inject it's kinetic energy into the wake to dilute it's drogue effect,That's where the drag is,behind the car.
If you cut a hole,now you've let the air out of the dam and re-opened the torture-chamber.And then there is the chance that ALL the air under the car will be turbulence,adding to the wake resulting in higher drag.

[luvit]

some folks fill their rear bumper with spray foam.
i don't know if they made scientific measurements before and after spraying foam.

[MadisonMPG]

Belly pan.

[Christ]

Originally Posted by luvit

some folks fill their rear bumper with spray foam.
i don't know if they made scientific measurements before and after spraying foam.

Not likely...

[luvit]

not likely they took measurements?
or not likely it helped...

[Christ]

Originally Posted by luvit

not likely they took measurements?
or not likely it helped...

Measurements.

Most people don't bother, they just assume it works.

(Whatever "it" happens to be.) (Magnets.)

[aerohead]

on Dr. Morelli's CNR "banana" car,he did "vent" the rear bumper,however,the air was taken from BELOW the bellypan diffuser and allowed to communicate with the wake,via a series of slots between the back of the car and bumper fascia.
My guess,is that this was one of the "zero-lift" aspects of that car.
The important thing,is that he never allowed air into the "under-carriage,always keeping it below the pan.