Raising bonnet /hood -help airflow?

[Frank Lee]

Re: rain: that's exactly what I've seen on all my vehicles, and none of them have "bonnet guards".

[spacemanspif]

I see that kind of thing on my Focus but wonder how much is caused by the wipers blocking the air and keeping the rain from sheeting off. I don't have a deflector like Eddie25 either. My Monte Carlo has a 3" cowl induction hood and the rain on the windshield most definitely flows down and toward the center of the windshield in the area right behind the cowl. Because of this forum I have blocked off the holes in the hood that would be utilized for cool air induction with a carb since I am EFI and can't make my intake work with the cowl induction. For me the hood was for aesthetics but serves double duty as clearance for my intake manifold. They were open for about a year but after reading about front end lift and engine cooling on here I decided to cover them and hope for less lift at high speeds.

[aerohead]

Originally Posted by NickelB NL

And it would also help aero? Because i.m thinking about it too. I have foam forming "under" the wipers because of air (see pic). And was thinking of a small lip to attach in front of the wipers

I would have to say,it depends.
In Hucho's text,he has examples of detail optimization which date from before 1975 which includes hood angles.Other researchers have done follow on research of the same things.
For a given example,with increasing slope there is a drag reduction,after which
you reach 'saturation',where any additional slope yields zero benefit.
All cars designed since 1976 have used Volkwagen's detail optimization techniques.
The stagnation bubble at the cowl area of your car isn't really a drag generator.That burble area provides quasi-pressurized air for your ventilation system.The surrounding air just goes around this area with no problem.
I created a blister for my truck which reduces the angle between the 'cowl' and the windshield in lieu of a $3,000 GTP windshield.It will be September 2016 before I can tell you if it cuts drag or not.I do know that taping slanted cardboard over the entire wiper area didn't effect top speed of my CRX or T-100.
Some of the lowest drag cars created don't necessarily have 'steep' hoods.They do have exotic and extremely expensive windshields plus curved side glass which is completely flush.
It's more important that dramatic pressure spikes don't occur anywhere along the car's body.And this may have already been worked out with the standard vehicle.It would take a wind tunnel to prove it.

[markweatherill]

Don't forget that by raising the rear of a hood, you also raise the entire hood to some extent, creating a gap not only at the rear but all along the sides too.