Quote:
Originally Posted by vibrating_cake
Isn't the opposite true about the sealing at the windscreen side of the hood? Taking that off would try venting bonnet heat into a high pressure zone, which would effectively act as an auxiliary air intake into the bonnet that bypasses the radiator?
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Hot air has high pressure too. A temperature difference of 55deg C (100 deg F) gives about 18% increase in pressure. As per the picture, you would think that its easy for hot air to flow down. Rather, the air stagnates inside the engine bay, which can cause a drop in differential pressure across the rad. I would say that air leaks out to the back rather than being drawn out. I do not think that ecomodders would drive fast enough to have high aerodynamic pressure to force the hot air back in. One would need to travel beyond 90km/h which isn't very eco anyways.
See also
http://www.autospeed.com/cms/A_113157/article.html Unfortunately that article did not say what pressure that sensor is supposed to trigger, but you get the general idea.