need OPINIONS on cutting a vent into my hood.

[mavisky]

Which you won't see in our vehicles due to the complete lack of any sort of "under-engine" cover. All the air escapes out the sides and underneath the car.

 

[FrankNstein]

Hi Kyle,
Just ordered the wide vent for the Spyder, same as the one on the black car in the photo, only no bondo. Fiberglass style is $40. I didn't like the small one once I layed it on the hood, looked too small. That's what you get for buying from a tiny JPEG.
I plan on going to the 107.9 car show Saturday, so I'll throw the old one in the trunk. If I don't see you there, I'll swing past the dealership so you can try it on. I think matte black with racin' rivets would look cool on your car. A lot of RRE's race cars use two vents, this could be your first.
You have my number if you want it before Sat.
E.

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[mavisky]

Oh crap Eric, I think I forgot to make any mention of it on the local board, but I got my hood smashed and insurance covered the cost of a new vented carbon fiber hood.

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[FrankNstein]

Hood smashed? Youch. New one looks great.

 

[DGajre777]

That isn't going to do crap. Just like all the other holes people have carved into their hoods.

If you want it to EXTRACT air, you have to use a vent that induces a low pressure zone (IE the carbontrix hood vents). Otherwise you're just forcing more air into the engine bay (which will vent underneath the vehicle, further ruining underbody aerodynamics). Not to mention that it may interfere with cooling, as stated earlier.

I'm confused now.

So basically, my hood doesn't do anything to cool my engine bay? Even with the little raised section to make air go over the hood vent??

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More pics here - http://www.dsmtuners.com/forums/showthread.php?t=223863

 

[mavisky]

Yours should be fine, although at speed that middle vent may be less effective than the side vents. With the way the 2g hood is curved the rear half of that center cutout could be seeing direct airflow from the front of the car due to its size. Hopefully the front little lip is helping to kick enough airflow up and around at that point to reduce that from happening, but once again it's hard to say.

If you look at my vent, there's no vent open towards or even perpendicular to airflow. Now whether it's big enough or not is another question we'll have to find out over time.

 

[DGajre777]

Thanks for the info! I guess I'll be doing some testing with some strings this weekend.

 

[Defiant]

Yarn it and film it, we're keen to see what happens.

 

[leet]

I'm confused now.

So basically, my hood doesn't do anything to cool my engine bay? Even with the little raised section to make air go over the hood vent??

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More pics here - http://www.dsmtuners.com/forums/showthread.php?t=223863

It will keep it cooler, but I doubt they will act as vents. Probably will be intakes, with that air exiting under the vehicle (not ideal as it causes underbody drag, but for street use it doesn't matter).

However, do the string test and post up results. I'm curious to see how they act.

 

[jtmcinder]

Cowl induction forces air out, not in.

No, that would be cowl extraction (which is close to an oxymoron, given how that area is almost always high-pressure). Induction means the air goes in.

As the air passes over the opening, it creates a vacuum of cold air over the windshield. This allows the hot air from inside the engine compartment to escape letting the engine breathe cooler air and therefore running stronger and longer.

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Cowl Induction Hood - How It Works
Air glides over the cowl induction hood.
It then hits the base of the windsheild, creating a low pressure area, allowing the hot air to escape from the engine compartment.

Yes, PTeazer makes this claim. Problem is, several people have done the string test and - lo and behold - the air actually goes in.

Funny the way PTeazer gets the name correct - viz., cowl induction - and then makes a BS animated gif and BS claims as to what will happen. But given that it took quite a while to find anyone who has tested their hood, it seems that their claims have worked on many people.

The high-pressure area in front of the windshield extends quite a distance down the hood. Any vent within about a foot of the windshield will be an inlet, not an extraction vent, at least, at speed. Before cutting my hood, I logged about three hours of driving around at various speeds with my boost-gauge hose attached to various places on my hood.

- Jtoby

 

[jtmcinder]

DGajre -

Get out some string. That big vent is almost exactly where it should be (in terms of the location of the lowest pressure at speed). Plus, that ridge will probably make it even better than plain grating (as I have).

- Jtoby

 

[dr1665]

Oddly enough, I started a thread on another board about this subject exactly a year ago tomorrow. Harnessing the power of Bernouli's Law to generate lift that pulls the car downward at speed, while efficiently flowing air through the radiator and engine bay is something that never ceases to amaze me. Theoretically, Formula 1 cars make enough use of these principles that they could drive upside down at speed.

Proper aerodynamic tuning (and this has NOTHING to do with aftermarket body kits) can yield more horsepower, lower operating temperatures, harder braking, tighter turning, greater high-speed stability, and even greater fuel economy. You can quote whatever source you want, but the rules of physics will work the same every time and only proper implementation of devices in the correct locations will result in their functioning as intended.

The general rule of thumb I use is this:

Where the air is forced AWAY from the car, there is HIGH pressure, and it will want to go IN.
Where the air is pulled TOWARDS the car, there is LOW pressure, and it will want to pull OUT.

I whipped this little image up to give an idea where the pressure is going to be higher (red) or lower (blue). This is only meant to visualize the rule of thumb above.

 

[jtmcinder]

Nice pic.

To be clear about Bernoulli: the faster the air is moving, the less static pressure it produces. (This is how an airplane's wings work.) That is why, starting less than a foot from the front edge of the hood, there is a large low-pressure area, even though it is still slightly rising. That's where my extraction vent is.

The role played by air moving away from the car is actually quite minimal in producing low pressure. However, dynamic pressure plays a huge role in creating some of the high-pressure areas (such as on the windshield and over the cowl). It is also why the STi hood scoop was increased in size: the location has low static pressure via Bernoulli, so they had to up the size of the scoop and overcome this problem using dynamic pressure.

Best page I've found: http://home.earthlink.net/~mmc1919/venturi.html

- Jtoby

 

[LTUDSM]

That what i did to my brothers hood

1st he bought a oem cf hood,
2nd i bought a subaru STI cf hood scoop
3rd i cut a hole int the center of the hood
put the sti's scoof in the oem cf hood
those peaces that left off the hud i made a nice headlight covers
the pic is right here what do you guys think????

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[PieEyedPiper]

Neat.
Got a side profile?

 

[mavisky]

Interesting, probably keeps the exhaust manifold 10 degrees cooler and adds a ton of drag, other than that I'm not sure what to say.

 

[LTUDSM]

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[LTUDSM]

Interesting, probably keeps the exhaust manifold 10 degrees cooler and adds a ton of drag, other than that I'm not sure what to say.

uyoure right and plus it has a better air acces to the filter cause the filter is not that far from the scoop entrance