Has anyone tried the cowl scoops that Moss Mini sells.....the abs plastic ones for added air flow?

 

Randy from M7 has them on his car. They are probably the best from a function standpoint but I like the looks of the Oricaris the best. Peter at M7 told me a while back that they were developing a cowl scoop but I haven't heard anything about it lately. Here is a photo of Randy's MINI:

 

I believe that Randy Webb (an aviation professional and MINI guru) did quite a bit of aero testing at the site of the cowl as he was contemplating developing a scoop product. If I recall, he discovered that the cowl area is actually within a neutral or slightly negative air pressure area. Thus, unless the height of the scoop is significant (say, 8"-10" or so...enough to enter the positive air pressure flow over the bonnet), the only effect these scoops will have is purely cosmetic.

On the other hand, there are lots of cool things out there that serve only cosmetic purposes...a CF bonnet scoop, for instance.

Theo

 

http://community.webshots.com/photo/...51533390WrBrMi

I have the Oricaris On Merlin

 

Please excuse the stupidity, what are they supposed to do?

 

I have the CF Cowl Scoop on my car. It surely makes the car looks nicer since I have an EB MCS, CF bonnet scoop and CF Hamann Lip.

But somehow it makes some noises at 225Km/h. Only on the right side, maybe due to the fitting since I used Silicon to glue it to the body.

 

This sounds reasonable to me. Most cars have a negative pressure area at the base of the windshield. This is the reason tha cowl intakes on old Chevy muscle cars are open in the rear at the base of the windshield. I would bet that cowl scoops on the MINI would not increase airflow and may actually reduce it.

 

Does it stand to reason then that if the cowl scoop were turned around, there would be airflow into the vent? You mean there is an eddy in the air current over the hood/windshield area where the airflow is counter to the normal direction?

dan

 

Not an eddy, just a lack of airflow (neutral pressure). With no airflow, it doesnt matter which way the scoop faces.

Think of it this way: air flowing over the MINI is directly affected by its profile. One might look at that profile and see the body affecting the airflow in three layers: (1) the air being encountered by the nose and forced up and around the bonnet, (2) the air that is above the nose but is destined to hit the windscreen and be forced up and around the roof, and (3) the "clean" air layer above the MINI.

In reality, this distict division of the layers does not exist. The airflow in the upper part of each layer affects the airflow of the lower portion of the layer above it. Thus, the airflow over the bonnet (layer 1) will be angling upward as it flows over the nose. At this height from the bonnet, it encounters and affects the direct airflow toward the windscreen (layer 2). Layer 2 airflow is then forced upward by layer 1 before it reaches the windscreen. At this point, the layer 1 and layer 2 airflow is well above the cowl surface. Layer 2 then encounters the windshield and strikes it some distance from the bottom edge. Thus, layer 1 has affected layer 2 at the car's nose, forcing layer 2 to to be angled upward toward the upper portion of the windscreen.

Layer 3 is also affected by layer 2 in a similar manner with its airflow being directed up and over the roof at some height; one might expect a similar neutral or negative air pressure in the mid to rear roof surface. The sunroof spoilers attempt to move the neutral/negative pressure directly over the sunroof opening. The effect being an attempt to lower noise and neutralize air currents.

It would be very enlightening to see the MINI in a wind tunnel and record the detail its aerodynamic profile. However, you can do a bit of testing yourself! Take 2" sections of a light yarn and tape them to the MINI's body at key points in the airflow. As you drive, observe how and in what direction the yarn moves.

This is a simple explanation from someone who is NOT an areodynamics engineer. My apologies if I am not using the right terms.

FWIW,

Theo

 

Koopah, that was a nice explanation The angling of the airflow upwards by the nose of the car is exactly why the area above the hood on many cars is 0 to negative pressure (relative to normal atmospheric pressure) at speed.

I don't think, however, that necessarily translates into negative pressure at the base of the windshield. The reason the cowl intakes faced rearward on the old Chevy muscle cars was because that was an area of "HIGH" pressure. As the car was moving at speed air starts piling up against the windsheild and builds up pressure, more and more as the car goes faster. Its that pressure that deflects Koopah's layers 1 and 2 up and over (and around) the car. If there is an opening at the base of the windshield with lower pressure, as in the Chevy cowl intake, the air is pushed into that as well.

So it does stand to reason that, if turned around toward the windshield, and if the openings are sufficiently close to the windshield, airflow would be increased into the vents.

Of course without measurements this is purely supposition. (Except the part about the Chevy's, that is historical engineering fact.) There are a ton of unknown variables such as how thick the pressure layer is, whether the shape of the scoops themselves is enough to disturb the airflow and raise or lower the pressure at the opening, etc. etc. But in terms of broad concepts the scoops would have a much better chance of working if facing the windshield than if facing forward.

I also agree, though, that they can look very cool regardless.

 

OK

Now, let's experiment...

Tape a number of 2" sections of light yarn before and around the cowl vents. Also, tape a double row of yarn on the windscreen under the wipers. In calm weather, drive at 40mph/64kph and at 60mph/100kph. Note the behavior of the yarn. Better yet, have a brave passenger take some pictures out the window.

Theo

 

yarn shmarn put some dabs of colored oil at the base of the windshield and near the cowl openings, drive around, then take the pictures. apply zaino before starting experiment.

 

I’ve watched water movement on the hood after a down pour and after a wetting at the car wash; the water at each side of the center hood hump moves slower in relation to surface water on the sides of the hood. Also, beaded water will stay intact at the base of the intercooler hood scoop trim ring for much longer than anywhere on the hood. Two places one would think the water should be flying. That seems to indicate the blunt front end is pushing most of the air up rather than snugly flowing over the hood. Next, the area under the cowl is dry after driving in the rain, another sign of a pressure difference.

 

I've done the measurements. Years ago.
The cowl area is under slight positive pressure but you don't really see any effect until you're exceeding 50 MPH
Copied from an old post

 

Spoken like a person who has had to clean the remnants of a Rotax oil leak from a plane's cowl!

Theo

 

Thanks to obehave!

Would it be correct to surmise from your data that the nature and amout of positive pressure found at 50mph+ would not be substantially aided by either a front or rear facing scoop? Perhaps I do not have a appreciation of the magnitude of the air pressure data you present.

Thanks,

Theo

 

theo,

i agree, thanks to obe wan!

if you assume, just for argument, that you have about 20 psi of boost, that 0.06 extra psi ( x 1.5) amounts to a factor of 0.005 or 0.5% or about 1 hp!!! so i don't think that the "ram air" effect is all that much here.

i think what's far more important is reducing the bends / convoluted flow path losses to the tb. witness the hai gains....

may the colored oil flow be with you...:smile:

 

Yea. What he said

 

With all that being said, how effective is a CAI which supposely draws air from those vents?

 

I am curious as well.......is there a "ram" air mod for the Alta CAI?

 

This thread may show some light on that question.

 

right~0n the money w/this write up!

 

I painted mine black to match the roof.

 

not sure about the positive and negative pressure but I am very sure about the positive vibe....very nice

 

Thanks! The ol' butt dyno is telling me that it's working!

Btw I know I posted this in some other thread but both cowl scoops are function since the passenger side leads to the driver side.