Quote:
Originally Posted by hispanicpanic
I don't think coast down tests would be able to provide the resolution necessary to test some of these items. Perhaps i can fit an engine management system and monitor injector duty cycles and back calculate the fuel required to maintain 80mph with each..... Hmmmm....
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I don't think injector duty cycles are going to give you reliable data for drag comparisons. Why not try something like throttle-stop testing? Your car is old enough that it has a cable-operated rather than electronic throttle.
Details in this thread.
Quote:
Originally Posted by Blacktree
Not to be rude, but I think you're operating under a false premise. There is no "parachute effect" with the side windows open. Actually, quite the opposite. The air flowing across the window openings causes a pressure drop in the cabin. If you then open the cabin to the rear wake, it will suck in air (and dust, and exhaust fumes) from the rear wake. It will also increase aero drag, because the car is pulling air forward, into the cabin (which means the air is pulling backward on the car).
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You may very well be right. The original post is an example of intuitive prediction that does not work with fluid flows.
A simple tuft test on my truck showed the wake behind the cab is the same pressure as the air inside the cab with the windows closed:
With windows open, air flows into the cab through the rear window and out the sides:
OP should put tufts on his windows and see which way the air flows with them open.