Sunroof shield removal question

[squriellord]

Hello everyone!

Today I removed the sunroof cover/baffle/shield from my 1991 Legend. It's a plastic piece which screwed onto two clamps which were hooked inside the sunroof opening. I guess it's purpose was to prevent stuff from flying into the car when the sunroof was open. Pictures:
Before

After

(holy smokes it was dirty underneath it!)

Now, since this reduces the frontal area, it ought to lower the CdA. However, since the sunroof is now exposed, won't the non-smooth surface where the from of the sunroof is cause a flow separation? (and increase Cd...)

I'm expecting a bit of wind noise but hopefully nothing too unbearable.

Aerodynamics experts, what are your thoughts?

-Squriellord.

[alohaspirit]

Originally Posted by squriellord

Now, since this reduces the frontal area, it ought to lower the CdA. However, since the sunroof is now exposed, won't the non-smooth surface where the from of the sunroof is cause a flow separation? (and increase Cd...)

It does reduce your CdA (back to stock numbers)
But it wont cause flow separation unless you open your sunroof.

[ChazInMT]

I used to have a 1990 Plymouth Laser/Mits Eclipse. I had a sun roof put in and had a little deflector for it. Without the deflector and the sun roof open, my car was an enormous coke bottle, there was this loud low pitch vibration from having the sunroof open. I don't expect the deflector of yours was preventing this.

The reason for your deflector I'd imagine was not for debris management, but rather it helped create a low pressure area so when you opened your sunroof a few inches, it would really draw a huge amount of air out of your car increasing circulation. And it probably helped with wind noise as well.

I think you're better off not having the deflector, and your "non-smooth surface" concerns are unwarranted. Significant flow separation requires more drastic obstacles than what the little bumps on your sunroof present....don't worry about it.

[squriellord]

Originally Posted by alohaspirit

It does reduce your CdA (back to stock numbers)
But it wont cause flow separation unless you open your sunroof.

Originally Posted by ChazInMT

I think you're better off not having the deflector, and your "non-smooth surface" concerns are unwarranted. Significant flow separation requires more drastic obstacles than what the little bumps on your sunroof present....don't worry about it.

Okay, thanks guys. I'll won't loose any sleep over it! The sunroof stays closed most of the time anyways.
I think that any FE increase would be very small, but 'it's the many little changes which make the difference'.

[Frank Lee]

That thing you took off wasn't there to begin with.

[SwamiSalami]

Originally Posted by Frank Lee

That thing you took off wasn't there to begin with.

Nice call, Frank Lee. Being that we refer to the art of boosting a car's efficiency as "ecomodding", what would we call the art of making a car less efficient?

[Frank Lee]

It's usually called "hot rodding". Sometimes I call it "Rice", and I have some other names for it that are not printable here.

[SwamiSalami]

oh, c'mon, Frank Lee. We can do better than that. I'm getting tingly hair on the back of my neck. Perhaps we should persuade the powers that be to provide us with a forum topic of this sort. This way, when we see this happening, we can photograph or document it for other ecomodders' enjoyment.

Because, it is quite enjoyable. At first, it was frustrating, but now I just laugh. Another great example is rims.

See? This is a great topic.

[larrybuck]

OK! That's a good start. We want to save fuel, and make the drivetrain last longer, right?

Mask it off, and spray that sunroof top flat black to cool your interior, and can some AC usage!

Oh how I despise sunroofs! I feel better now!

[SwamiSalami]

Originally Posted by larrybuck

Mask it off, and spray that sunroof top flat black to cool your interior, and can some AC usage!

Hey Larry, don't you mean white instead of black? Black absorbs heat, while white reflects it.

all the best