Speed Holes for MPG?

[Sven7]

Originally Posted by johnunit

Some of the people laughing at "speed holes" are showing a degree of ignorance of high-level import drag racing. There are tons of VERY fast (think 8-10 second 1/4 mile with FWD) cars out there with so called "speed holes" in the rear bumper. I'd have to imagine that it's a car-by-car thing though. Many cars would probably see losses.


GO-AUTOWORKS.COM Rear Diffusers, Splitters, Front Ends and Carbon components

from the thread below


rear bumper diffuser - 8th Generation Honda Civic Forum

another thread on the topic:

rear bumper holes? - Honda-Tech







There are certainly better solutions, but for CHEAP and within certain rules, it does have benefit.

I don't see anyone proving their theory. Everyone says air catches in the bumper because they don't know about the aero template type things. There's no way the airflow is making a 30* turn upward after the rear axle to catch on the bumper. I'll bet you they're just adding to the turbulent mess down there.

Still, if someone can find ABA or wind tunnel calibrated results I'm open to seeing them. I'm just not yet convinced by street racer logic. If it really worked wouldn't "speed holes" be in the "65+ efficiency mods" in the header of this website? Perhaps they haven't been proven to work...

[Cassem]

I saw a Tesla in the parking lot at work yesterday and I noticed a sort of mesh on the lower rear bumper. I thought it was speed holes at first but I think what it was instead was a way to have the underbody turn up like an aerofoil and still retain that traditional rear bumper look.

[aerohead]

Originally Posted by Sven7

I don't see anyone proving their theory. Everyone says air catches in the bumper because they don't know about the aero template type things. There's no way the airflow is making a 30* turn upward after the rear axle to catch on the bumper. I'll bet you they're just adding to the turbulent mess down there.

Still, if someone can find ABA or wind tunnel calibrated results I'm open to seeing them. I'm just not yet convinced by street racer logic. If it really worked wouldn't "speed holes" be in the "65+ efficiency mods" in the header of this website? Perhaps they haven't been proven to work...

Subaru published an SAE Paper on the development of their Cd 0.29 XT sport coupe in 1986.
Lowering the bottom of the rear bumper,and floor of the trunk even with the belly of the car was one of their modifications to achieve lower drag.
Without the air-tightness of the bumper facia,their efforts would be scuttled.
Now if you want to run ductwork through this region with high static pressure,electric tube-axial fans,down to the belly diffuser,well then you're going to see an improvement up to a certain velocity,as Ferrari is demonstrating with their 599XX racer.
But in a 'passive' context,one should be rewarded only with higher drag.

[PAFirefighter11]

Bumping an old thread.. what about this though?

[viio]

Downforce definitely. Drag I'm not sure about.

[AntiochOG]

My Miata track racer friends all like to cut the bottom of their back bumpers off. Some remove the rear bumper all together. Supposedly this is netting them faster speeds on the straights.

[Otto]

If the rear bumper cover was acting as a drag chute, and you cut holes in said drag chute, you'd probably reduce drag. So, "speed holes" may be a perverse way to partially correct poor design.

Better not to have a drag chute, but using an undertray or such to smoothe the airfow.

And, start with a decent plastic garden edging air dam in the front, to keep the draggy air from clogging up the underside of the car in the first place.

[kach22i]

Originally Posted by Blacktree

Some of the exotic sports cars have air vents in the rear bumper area. But those cars have the engine in back, and are venting air from the engine bay. This is probably where the ricers draw their inspiration. But your average commuter car doesn't have an engine bay in back, to draw air from.

Exactly, yet another example of Porsche envy.

Drilling holes to remove weight. - Pelican Parts Technical BBS


Of course you can drill out any car to make it lighter, quite a few examples in this thread below (start at page-1).

Looking for ideas and/or pictures of drilled out parts - Page 3 - Pelican Parts Technical BBS

[jeff88]

So I was going to post this in a new thread, but then this one popped up.

Do these count as air holes?

[aerohead]

Originally Posted by PAFirefighter11

Bumping an old thread.. what about this though?

It's the 'look.'
If you're a B-Spec racer and you actually do track time,where down-force can reduce orbits on the course,well then you'd see a benefit.
For fuel economy the lowest drag diffuser is at a 2.5-degree up sweep.Nothing steeper.It's not sexy but it's good science.