Just toying with this idea at the moment but would be interested to hear if anyone has tried this, or even if it would work.

I have a Forester and was thinking about using something like the Impreza bonnet air vents to provide an exit point for hot engine bay air. If they were placed each side of the tmic air scoop and the vents turned 180 degrees so that they faced the windscreen, then is the forward motion of the car going to force hot air out and in any appreciable amount to be worthwhile ?

I could use just an open mesh style vent but thought that the Impreza style ones would give a little more protection from rainwater getting in.

A daft idea or not !

Cheers

jbl

 

Depends on where you position them, and whether you actually need hot air exhausting from the engine bay. I would expect the standard airflow to be out and under the car, so putting exhaust vents in the bonnet will upset engine bay flow. If you've not done anything under the bonnet that needs extra cooling, then cutting vents in where they shouldn't be will only at best equal what you've already got, and most likely make engine cooling marginally worse.

It's quite a complex subject, but suffice to say that front end aerodynamics on a car are not what you might at first glance expect.

 

Thanks for that Silent Running.
A little more complex perhaps than I first thought....

I shall ponder a while........

Cheers

jbl

 

my mate has his main scoop on his impreza backwards - could work the same way

interested to see pics if you do this as i'd quite like the smaller side vents on my Foz

 

Basically air naturally flows from high pressure to low pressure areas if allowed to. The engine bay on front engined cars is a high pressure area from all the air being stuffed into it from the front. The underside of the car is usually low pressure. Air naturally is pulled out of the engine bay and in the case of the Impreza, along the sides of the gearbox and out. Putting vents in the bonnet WILL work to extract engine bay air, as long as they're not too far back (the scuttle panel area is another high pressure zone, hence why your fresh air intakes are there). The question is whether extracting air out and upwards is going to interrupt the natural flow rearwards and under. If you're going to extract from the bonnet then the best place is where WRC cars and Evos/Elises etc have it - just rear of the radiator(s) and shrouded to take virtually all the radiator exhaust flow out. But on a Subaru that's a major reorganisation of the engine bay.