Quote:
Originally Posted by robones
I think unless the drag is compared to a non modified z we can't really determine how bad or how little a difference drag makes. All I know that I lean towards it making more of an impact then not.
I remember watching a myth busters experiment about leaving your truck bed hatch open or closed while driving to increase MPG. It was found that you will lose about 3-5 mpgs if you leave the hatch down instead of up. All because the turbulence thats created in the bed of the truck while the hatch is down. So you can see how much harder the truck was working just to keep the same speed. 
Again this argument only pertains to certain exhaust designs as previously mentioned. |
Oh dear, the mythbusters correlation.
Okay, there is a question of scaling here. The truck bed is quite a big surface area that changes / alters the air performance characteristics in the area. The exposed square footage of the exhaust is significantly less. Therefore while there is SOME effect, it is minimal at best. Do the proportion, take the truck hatch and the exposed area of the exhaust, and divide them to find the ratio. It'd be like...5% maybe, at best. edit: You also would need to consider the volumetric air flow in the area. The majority of the air is going up and over the car; that's how most are designed (but air still gets underneath, as I note later). Therefore there would be a slight bias, or increased impact, corresponding with aerodynamic improvement on the upper exterior of a vehicle.
To fully consider the question, you'd have to consider the better air flow through the engine and the reduced weight an aftermarket exhaust gives you, and trade it against the increased drag coefficient. To me, it's a waste of time, the drag coefficient is such a minor issue that the benefits of swapping vastly outweight the deficiencies. Or do a CFD model, run it through a theoretical wind tunnel, and then see what you get for drag coefficients of the vehicle with stock and aftermarket exhausts.
ken - what do you mean by significant amount of air? The Z isn't designed to push air around the vehicle, it lets it go through. The front "scoop", or intake area, isn't designed to limit air from going down. If there was no chance of air going through the bottom of the car, we wouldn't need race-type wings to increase downforce and keep the car planted at high speeds.