Speed Holes for MPG?
 

The "speed holes" are a fad in the tuner circles. Basically, they just cut a bunch of holes in the rear bumper. Supposedly, by ventilating the rear bumper, it reduces the aero drag.

Has anyone tried such a thing on an "ecomodded" car? And was there any measurable benefit? I have my doubts, but wanted to ask anyway.

The premise is faulty and the execution is usually even worse.

...they make the car go faster...

http://www.youtube.com/watch?v=XVV_COOey0E

I haven't seen "holes" but I've seen some cars like this

http://www.bodykitsuperstore.com/ima...nda/890179.jpg

If they want to make a difference on cd they should have boat tails. And if they're racing I'd love to see the faces on the other people who are racing them haha :eek:

holes
 

Opening holes in the rear bumper would increase the drag,not lower it.The bottom of the rear bumper should be close to the elevation of the underside of the car.You want it to pool dead air up where all the naughty bits are,allowing the air underneath to flow smoothly to the rear.
If you're having a problem with wheelspin at high speed,then perforating the rear would allow low base pressure of the wake to communicate forward under the car to provide downforce and traction.It would cost you speed though.
A rear spoiler would be better.

Assume anything the ricers do is wrong, no matter what the intended goal is.

I spent an afternoon with a guy who was head mechanic fora Le Mans team which won its class. He was backed by a BIG factory which spent a LOT of money on windtunnel testing.

Any air which gets under the car slows the car down by causing drag. More air, more drag. This is known by ANYONE who races, and front spoiler height is heavily regulated by every sanctioning body.

Once the air gets under the car, get it OUT at the back. Run the highest possible bumper with the most amount of the biggest holes.
Any amount of restriction in getting the air out the back of the car causes upforce and drag.

These rules apply to any car which can't run aero tunnels, which are defined to be any car with a ride height of over 2 inches (you can't make very effective tunnels with 2 inches of ride height.)

we are not talking about fully built race cars... we are talking about the punk ass ricers civics with fart cans.

I don't see any "racing holes" in this, or any other, Le Mans car I've looked at.

http://upload.wikimedia.org/wikipedi...1981-08-15.jpg

Le Mans cars can sometimes have too little aerodynamic drag. They turn into lifting surfaces, to the detrement of their drivers.

http://thatcarblog.com/wp-content/up...rn-300x291.jpg http://i213.photobucket.com/albums/c...05338251_o.jpg

Pure drivel. :rolleyes:

or you can seal up the back with an nder belly pan

this is lucking from the rear passenfer tire under the car:

http://i678.photobucket.com/albums/v...lsplats122.jpg

from the driver side rear:
http://i678.photobucket.com/albums/v...plats012-1.jpg

from the rear center:
yes, there is a opening for trapped air to exscape
http://i678.photobucket.com/albums/v...plats013-1.jpg

from the drive shaft/rear axle looking back (the yellow coroplast is blocking the glare!)
http://i678.photobucket.com/albums/v...plats014-1.jpg

LOOKING STRAIGHT`back from the drivers side,
http://i678.photobucket.com/albums/v...plats015-1.jpg

Here's a picture of what I'm talking about.

http://ricercarmods.com/wp-content/u...er-mods-23.jpg

Presumably, the idea here is to reduce the "parachute effect" caused by the rear bumper scooping up air from under the car. This still leaves you with a "partial parachute", though.

I can see something like this helping to get air out from underneath, on a race car. But road cars have an impact beam blocking airflow through those holes.

Personally, I think that encouraging air to flow through the underbody would be counter-productive, from an aero drag standpoint.

This is from loosing the vacuum under the car. NASCAR had major problems with this until they added roof flap vents.
When a car is low in the front, smooth on the bottom with a slight increasing taper, it creates many pounds of down force and a little drag. In racing downforce is usually > drag on the heiarchy list.
Stock car guys and drag racers will try nearly anything for some speed. Many smaller levels of racing have very loose rules. One guy had a huge fan and flex skirts. Huge amount of downforce, cornered like nothing, took too much HP from the engine. They wouldn't allow the version with an aux engine for the fan :( Even with that level of "try anything" I've never seen speedholes.

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.

That said, I think it would be interesting to try something like that in one of the more affordable mid / rear engine cars, like an MR2 or a Fiero. You'd probably have to chop up the trunk, though.

Err... Maybe because it's all hole? That is, the upswept underside of the rear end removes the lower part of the rear bumper that the ricers would be drilling their "speed holes" in.

The ones on the sides are for brake venting I think.

Whoever said the bumper rebar would get in the way: people take the rebar out for "weight reduction".

There is a simple solution to speed holes: keep your bumper stock and add a full belly pan.

The NASCAR roof flaps keep the car from launching when it's going backwards. The Lemans car pictured managed to launch itself while going frontwards.

Smaller levels of racing indeed! The cars I believe you're referring to are Jim Hall's famous Chaparral 2J Can-Am "sucker car" and the copycat Brabham/Alfa BT46 F1 car.

http://29.media.tumblr.com/tumblr_lf...9ygko1_500.jpg

http://startinggrid.files.wordpress....3/bt-46b-1.jpg

Yeah, smaller levels of racing, like the SCCA and FIA. heh ;)

And for the record, the "sucker cars" were banned by the racing authorities... because they were too good.

WOW, I wasn't aware of those. Jim Hall I can claim as "before my time"
Until today I had only seen this at entry level racing. Thanks for pointing those out. Guess that's where the guys I saw pulled their ideas from !

On the nascar flaps, apparently you've never seen the rear go up on one of them and run down the straight on its nose........ don't make turn 1 very well though :( Yes, they do also work when the car gets spun around backwards as well.

what a great ad for MOBIL ONE!!!

Just wanted to quote the pix again :thumbup:

racing
 

I basically agree with your comments with respect to the context of dedicated racing vehicles,however none of this is germane with respect to the fuel economy of daily drivers operating on public roads and streets.

A great deal of the items that ricers use to improve performance of their cars is actually counterproductive (evident in the amount of black smoke that comes out of the tailpipe of these fart can mufflers). If you have holes on the back of your bumper, you would actually encourage more airflow to your rear bumper and create a drag. I would be curious to see this theory tested in a wind tunnel. I imagine that the rear bumper area would do the same as a pick up bed only upside down. Instead of drilling holes, why not just remove the bumper?:turtle:

or just seal up the bottom!

But then where would you mount the expanded metal ?????

Whats the difference between this:

And this (besides the top one really working)?

The top one doesn't make your car look faster.

Yes- why modify your car in an effective but invisible way when you can look faster and go slower? The great thing about ecomodding is you can be effective and visible without spending lots of money.

Just imagine in the future if teenagers did stop-light MPG runs instead of 1/4 mile races.

I suppose a new way to visually identify retarded high school car modifiers was needed (as if the sub-woofers and fart cans weren't enough :rolleyes: ) since back in the day everybody jacked the rears of their cars about a foot up in the air so as to look like fast Funny Cars, but now that most everything is fwd that doesn't make sense.... hey, wait a minute, it doesn't have to make sense. They could still do that!

:D:D:D:D:D:D:D:D:D

lol

:thumbup:

One of my life goals is to install hydraulic suspension in my '81 VW Rabbit. Three wheeling in a FWD economy car doesn't make sense, but it would be fun as hell.

And after all, isn't car modification supposed to be fun?

Frank lee....
you ask it doesn't have to make sense

i provide!!!
http://www.youtube.com/watch?v=UkTRn...layer_embedded

Somewhere, out there, someone actually thinks that is cool! :eek:

Yeah,
there is a name for it.....bazokaka or something. Its considered 'art' actually.
basicly somepeople just have way to much time on there hands!

*raises hand* :p

Seriously, though. Where did I put my keyhole saw?

Below the rear bumper of my '81 Datsun.... factory go-fast holes! :thumbup:

The RICE brigade are 30 years behind the times :D

I could model this in CFD if it helps?

Don't confuse bosozoku with ricers. They're very, very different. I throroughly enjoy bosozoku bikes and cars but still hate ricers.

Bozosuko?

It's hard to spell!- Bo so zo ku :)

Japanese motorcycle gangs, originally. They imitate and many times exaggerate Super Silhouette racing and other 70's and 80's phenomena through bike and car modification. There's a certain charm to some of their cartoony custom creations. If you google it (bosozoku or zokusha are the same thing) and can't stand it, try shakotan ("low down") or kyusha (Japanese classic car) and work your way up. :)

Here's a nice mild boso example from back in the day. Nowadays people mostly do this style because they dig it, not because of any gang affiliation.

http://www.bosozokustyle.com/sites/d...elica-aa63.jpg

And a beautiful shakotan ("low down") Kenmeri Skyline. This style of wide wheels, stretched tires and low suspension evolved into the "stance movement" of today.
http://lowdownspirit.files.wordpress.../bosozoku4.jpg

See? Not so bad.

Also remember the cars they're imitating weren't subtle in the least, and coincidentally, were mostly dictated by aerodynamics! (Don't you love when things go full circle?)
http://www.motormavens.com/emAlbum/a...lvia-impul.jpg

That black Skyline is so reminiscent of a 60's Barracuda, HOT!