Speed Holes for MPG?

[Sven7]

They're very handsome cars, along with the first gen "hakosuka" (Say ha KOH s'ka). Find both in Hot Wheels form at your nearest big box store!

[Frank Lee]

I (mis)spelled it bozo-suk-o on purpose, and I also thought I was pretty dang clever doing so.

The Skyline is pretty sweet tho'!

[viio]

Well I modelled 3 holes into my 1:1 scale 3d model of my car, and ran CFD on it. The holes cut through the bumper and come out in the space behind it which catches some airflow near the spare wheel. The colour contours show air velocity at the back of the car.

Forgive me if I don't rush out and grab a drill - can't see much of a difference.

If anything, the top model (with the holes) appears to have a larger area of low velocity air - hence more drag.

[Blacktree]

Wow, you actually took the time to make a computer model. That's pretty awesome!

[KamperBob]

Originally Posted by viio

Well I modelled 3 holes into my 1:1 scale 3d model of my car, and ran CFD on it. The holes cut through the bumper and come out in the space behind it which catches some airflow near the spare wheel. The colour contours show air velocity at the back of the car.

Forgive me if I don't rush out and grab a drill - can't see much of a difference.

If anything, the top model (with the holes) appears to have a larger area of low velocity air - hence more drag.

If you look at pressure I'd expect suction effect across the back. If you look at flow I'd expect characteristic eddy currents to balance boundary conditions with forward flow in the center. Hard to imagine high enough volume of airflow crammed under any car for wake filling in the rear. Bumper holes in the center likely just fuel parasitic eddies. In a fair fight I'd expect a negative return at the pump. It's all conjecture of course. But that's fun too.

[ConnClark]

Originally Posted by viio

Well I modelled 3 holes into my 1:1 scale 3d model of my car, and ran CFD on it. The holes cut through the bumper and come out in the space behind it which catches some airflow near the spare wheel. The colour contours show air velocity at the back of the car.

Forgive me if I don't rush out and grab a drill - can't see much of a difference.

If anything, the top model (with the holes) appears to have a larger area of low velocity air - hence more drag.

How representative is your model to the under side of your car? Can we see a view from the bottom of the car to see what the pressure is like on the front of the bumper near the holes?

[botsapper]

My concern is that your model does not recreate the undercarriage structures. The models seen are comparable to vehicles with flat belly pans. There is no turbulent flow swirling underneath to supposedly escape through those speed holes, hence no difference in your comparison models. By creating 'holes' it creates more turbulent flow @ the back. A sealed bumper would preserve a cushion or separation bubble that would allow under airflow move smoother. An aerodynamic analogy but inverted is the proven advantage of a closed tailgate than an open tailgate of a pickup truck.

[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

on the older civics, air would catch on the rear bumper since it was open to the air moving underneath the car. Putting holes in the rear bumper would alleviate this problem. Of course a full diffuser would work better but that requires some decent skills with your hands and machinery.

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.

[botsapper]

A tasteful application of speed holes...and supercharger. Because 454 Cubic Inches Just Isn’t Enough: AMC Marlin Racer Gets Twin Superchargers | The Truth About Cars
The history of speed holes, perforations & louvering came from the aircraft industry and the hot rod culture, either to lighten the oa weights, cooling and for the cool factor. Today its still for the cool factor.
http://www.bearmetalkustoms.com/imag...mpledie002.jpg
http://www.littlemansspeedandfabrica...ication/06.jpg
http://image.hotrod.com/f/34824477+w...rt_rat_rod.jpg

[Frank Lee]

Some of the people laughing at "speed holes" are showing a degree of ignorance of high-level import drag racing.

Hah- spose I'm one of those!

FYI I'm fully aware of these racers, and just because they have these holes doesn't make them less stupid. The premise is just as faulty on the track as it is on the street.