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Old 04-27-2009, 09:40 PM   #21 (permalink)
Master EcoModder
Join Date: Apr 2008
Location: Michigan
Posts: 261

Bio Deezler (sold) - '03 Volkswagen Jetta GLS TDI
90 day: 50.78 mpg (US)

The Beast. - '03 GMC Sierra 2500HD SLT
90 day: 12.86 mpg (US)
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Yep Cd, we definitely think alike. Thanks! I was actually just down in my garage pondering a decklid extension.

The car is already super low though dude. Probably about 3" of ground clearance under the skid plate.

I agree on the VGs too. Worth a try for 20 bucks and the cool look, imo. I think the reason you (and me) are confused is that while they often tuft test well, showing better attached flow right behind them, or on rear glass, etc, we still have no idea what is going on above the boundary layer or further downstream. And in those cases where they do add frontal area, well, that might be more explainable. One thing I don't get is how people recommend to place them on the rear slope of the car such that they don't add frontal area. This makes sense in general, but if the air flow over your car is still attached where you place them, don't they still present drag on a nearly full speed air flow and thus add "apparent" frontal area? Ok, so not full speed air flow, but the same boundary layer conditions as you have further forward on the car in area that would add frontal area....?

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