Mustang kammback help
 

Can someone tell me if the profile of a 99-04 Mustang would benefit from a Kammback? I was thinking of trying some thing with Lexan or clear acrylic so its not too terribly noticeable. Im definitely not committed enough to try a boat tail. And if i tint the clear Kammback maybe people will think its some kind of louver thing.

http://i81.photobucket.com/albums/j2...oi/99stang.gif

http://i81.photobucket.com/albums/j2...ideprofile.jpg

I don't see why it wouldn't improve some. If it's noticeable is going to be hard to say. Reminds me of the Ford Mustang Fastback which in 1979 had a Drag Coefficent of 0.02 lower than the standard model. Mind you that wing you have off the back is about the same angle and may already be giving the car some of the benefit a kammback would have.http://www.allfordmustangs.com/photo...S-1280x960.jpg

This is actually mine.


http://img9.imageshack.us/img9/548/mustang2p.jpg


Its a far away shot so I just posted those two closer ones in the first post. It does have the curved spoiled and not the flat one that came on the 01-04. The only difference is that i moved it back from the stock location so it hangs off the end of the trunk. For reference, the more pixelated Mustang I posted has the curved wing in the stock location. But thats neither here nor there. The wing could go if it helps aerodynamics.

Another thing, I have no idea how people here are doing those layover shots with the ideal angle. So Im unsure how far or close my body is to being near that perfect curve.

I would say "Hmmm... that depends". It depends on how well Ford designed the aerodynamics of the Mustang in the first place. It could end up being a lot of effort for minimal gain. The rear wing may actually be helping reduce drag. Have you read the thread about the "Flat Bonneville-type spoiler"?

http://ecomodder.com/forum/showthrea...ler-14946.html

IMO there may be other low hanging fruit such as grill blocking and folding or removing side mirrors that my make more of a difference in highway mileage. A belly pan is a nice stealth mod.

I have now modeled three spoiler types, and tested two of them, with both tests discussed in the thread cocyclist recommends. First thing I would do based on what I have learned in the process is measure the angle from roof to spoiler top using a string. If it is in the vicinity of a 15* angle, build a Kamm from roof to spoiler. You might use the spoiler itself as a support or mount for a support. You might remove that spoiler. It likely produces drag for the sake of downforce.

I'm finishing a trunk lid project for testing, though I fully expect I might not use it in the end and go for a Kamm. Clear materials appeal to me also, because I want it to look fairly stealthy and I do not want to loose any more visibility than absolutely necessary. I also agree with COcyclist: the bottom of these cars is almost always an Aero mess so there is a stealthy way to improve your car's Cd. Lastly, look up "rear defusor" on this forum. You could use one--or an improvement over stock if you have one.

PS: nice looking car, man.

Floordford -

I did this one to match what I think is the exact center of roof camber. You can see the streamline template slightly forward of the windshield :

http://ecomodder.com/forum/member-cf...oof-camber.jpg

Then I aligned the template with the windshield, which might be the *WRONG* thing to do :

http://ecomodder.com/forum/member-cf...enter-roof.jpg

Finally, I overlayed the slopes of the templates, bot only from the end of the roof to past the rear bumber :

http://ecomodder.com/forum/member-cf...kamm-backs.jpg

From the above you can see that the slope in both cases is very close. In an ideal world you would design the kammback with the ability to slightly modify the sloping angle. In that situation you could "tune" the kammback with A-B-A testing.

CarloSW2

The limit is 30 degrees, and the Mustang is within that limit, plus it has a gradual curve. I think it's fine the way it is. I'd be surprised if you got a significant improvement from making your beautiful car ugly.


Instead, get rid of the fake side air intake and give it an air dam.

My understanding from aerohead is that 30* is for the spoiler, but the rear window exceeding 22/23* is the max for attached flow, and that even that would need a longer lead-in curve than production cars can accomplish. The ideal is still about 15* from what I have seen (the "template" and the "Prius"). That's just my understanding, if I understood aerohead correctly. Winkosmosis, you think that's incorrect? But I agree on the side intake and the airdam, of course.

Ooops... 30 degrees seems to be the worst angle, because airflow separates somewhere along the surface, instead of breaking at the top or staying attached

Article

The Mustang's rear window is 22 degrees according to my measurement

If it is like my about 22* window there is turbulence and a bit of separation toward the lower half of the window and trunk lid. See this wet tuft still: http://ecomodder.com/forum/attachmen...p;d=1308151076

The spoiler is there possibly to try and correct it, and possibly to produce downforce. Either way it must be producing some drag of its own. A clear Kamm that replace the 22* window and spoiler with a 14/15* clean slope would probably get the big ecomodder cheer. It could look cool too, I would think.

The closest thing to a tuft test has been rain. And there is definitely separation. It starts coming back to the rear window on both sides and does kind of a V shape. l\ /l
Ive thought of vortex tabs but ive seen many tests where they accomplish little.

By the way, thanks CFG83 for doing the image mash up. It gives me a good general picture of what needs to get made.

Thank you California98Civic for the compliment and help.

So do you think a flat drag style wing would accomplish the same thing? It might look more at home on the back of a Mustang anyhow. But it would make it look like a full on drag car. And I have thought about deleting the side scoops and testing with and without the fake hood scoop.

i think for the effort en material involved in a camback you could build a nice front and rear, undertray, and smooth out the center secion as well... i think when aeromodding you best go for the most unaerodynamic sides first the underside and the grille, smooth out the underside reduce or completely block the grille opening, see if oem style dams might look appropriate... all gains that don't alter the look of a car much

I wouldn't do that. I tried it. A flat Bonneville style spoiler, slightly angled up. I hit the template just fine. In an ABAB test I lost MPG. Note too that winkosmosis corrected the post you're quoting. Personally, I love the suggestions you are getting about working with a front air dam, undertray, and side false intake deletes... these are low fruit that will almost certainly generate gains without changing your clean ride's look much at all. Even if you keep the side intake body moldings, do the other things. Those mods are on my own list. If I had not gotten distracted into these time consuming tail-end projects, I might have done the airdam and rear under tray by now. One of the coolest things about these aeromods for a car like yours is you can tell folks who ask that they produce better FE without reducing horsepower and therefore also increase your car's top speed.

Ive wanted to do an under body tray but have yet to be able to find low cost 4'x8' coroplast sheets. Te cheaper it is the sooner it will pay for itself. Ive got a few other things id like to try if I had a good amount of coroplast or cheap sheet aluminum.

I lately did a wiper and antenna delete and got 32 highway. Then on the exact same stretch did a passenger mirror delete, upper grille block, adjusted my cold air intake to take in only hot underhood air and I put foam around the headlights to gap seal. Those mods achieved 34mpg highway. Thats in the area of 50% improvement over the EPA 23mpg highway it gets from the factory. Im wondering if it can get to 38 on the highway. 40 may be too optimistic.

Whoa, you really got to 34mpg highway? Was that downhill with a tailwind?

Well it was a 160 mile down and back from Nashville to the Alabama state line on I65. Its a fairly hilly drive so some of it I was able to EOC. My speeds for most of the trip was 55-58. But a few times I would speed up as I wend down a hill so my coast would last longer. Back in March coming back from the Gatlinburg area going to Nashville I did 33mpg with the cruise control on 60. But it kind of doesn't count seeing that it was just one direction.