Speed Holes for MPG?

[Frank Lee]

Originally Posted by drmiller100

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.)

Pure drivel.

[mcrews]

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

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



from the driver side rear:


from the rear center:
yes, there is a opening for trapped air to exscape


from the drive shaft/rear axle looking back (the yellow coroplast is blocking the glare!)


LOOKING STRAIGHT`back from the drivers side,

[Blacktree]

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



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.

[JasonG]

Originally Posted by t vago

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



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

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.

[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.

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.

[jamesqf]

Originally Posted by t vago

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

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.

[Sven7]

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.

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.

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.

[wdb]

Originally Posted by JasonG

This is from loosing the vacuum under the car. NASCAR had major problems with this until they added roof flap vents.

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.

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

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.

[Blacktree]

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.

[JasonG]

Originally Posted by wdb

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.

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.