A fellow friend and BMW owner, Gustave, who's also a Phd in Fluid Mechanics, had this to write...

"Some of you may hear me go on about hood vents and wonder what the heck I'm talking about.

Here's a picture from test data in a wind tunnel that quite descriptively shows why you might want to place a hood vent near the front of the hood, not near the back.

The length of the arrows represents the local lift coefficient, either positive (into the vehicle surface) or negative (away from the vehicle surface).

Note the very high lift near the front of the hood where the flow turns the corner. This translates to negative pressure in this area. Similarly, near the rear of the hood, the cowl, we high positive pressure, which is why all production cars have inlets for their HVAC systems in this region.

Just FYI type of stuff..."

Gustave

 

Does that mean J's style hoods are efficient?
Matt.

 

I guess that would mean that a j's or amuse style would be more beneficial aerodynamically than a top secret or mugen?

 

That's also why many old American muscle cars (think Mustang Mach I) had rear-facing "cowl-air" intakes on the hood, i.e. with the opening just in front of the windshield.

 

If I read that image correctly, then, the cowl does not need to stand into the wind, but merely have an open hole near the front and rear of the hood. A cowling of any sort would seem to screw up the airflow since the data points are mentioned as normal vectors to the hood surface.

 

[QUOTE]Originally posted by wantone
A fellow friend and BMW owner, Gustave, who's also a Phd in Fluid Mechanics, had this to write...

"Some of you may hear me go on about hood vents and wonder what the heck I'm talking about.

Here's a picture from test data in a wind tunnel that quite descriptively shows why you might want to place a hood vent near the front of the hood, not near the back.

The length of the arrows represents the local lift coefficient, either positive (into the vehicle surface) or negative (away from the vehicle surface).

Note the very high lift near the front of the hood where the flow turns the corner. This translates to negative pressure in this area. Similarly, near the rear of the hood, the cowl, we high positive pressure, which is why all production cars have inlets for their HVAC systems in this region.

Just FYI type of stuff..."

 

No, it's a recent discussion we're having over in the M3 boards.

 

FWIW, I recently went from a j's style hood to an authentic mugen hood. Maybe due to the configuration of the openings, but my engine seems so much cooler when I pop the hood.

 

[QUOTE]Originally posted by Kekoa
FWIW, I recently went from a j's style hood to an authentic mugen hood.

 

Wantone,
That describes lift, but what about flow. Would air circulate, going from high pressure to low pressure, with the vents being the path of least resistance?