123212321 said:

You don't understand. Hood vents work the same way that airplanes fly. It will suck air OUT of the engine bay.

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What you seem to fail to realize is that hood vents, unless engineered, do not work to cool the engine bay. The same principle that allows airplanes to fly will push air from the hood into the engine bay and thus reduce the volume of air moving through the radiator which will make the engine over heat.

Don't pretend to be an aerodynamics expert. Have done some pressure testing on my STi and GSX though. Think I measured 8-10" water pressure static hitting the intercooler on my forward facing intercooler scoop on my STi. A rear facing hood scoop like Carbon trix mounting middle/ forward on the hood would provide pressure relief and cause air to exit thru the top.

All depends WHERE on the hood you place it. Base of windshield is a high pressure zone, upper rear nose of hood is a low pressure zone. Adding an abrupt lip also creates a localized low pressure zone anywhere you mount such a feature (i.e. rear tail, underadiator "air dam" etc.).

Manometer is good, a Magnehelic pressure differential gauge better. I own a 0-10", 0-100" and they are EXTREMELY useful for testing purposes. Things like testing intake pressure LOSSES and external surface pressure testing, stuff like that.

Theory is good, testing better. Buy the above mentioned gauge, tape one pressure port vaccum hose ABOVE the hood, the other pressure port BELOW the hood. As mentioned, depending WHERE on the hood you measure you may see positive or negative pressure differentials. If you want air coming in for say an airfilter ram duct, base of hood is good or face of bumper. You want an exhausting duct then rearward facing middle of hood is good. All depends on what you want to do.

pboglio said:

All depends WHERE on the hood you place it. Base of windshield is a high pressure zone, upper rear nose of hood is a low pressure zone. Adding an abrupt lip also creates a localized low pressure zone anywhere you mount such a feature (i.e. rear tail, underadiator "air dam" etc.)

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Thanks for the for the details. I didn't want to get too in depth so tried to generalize as much as possible. It's nice to hear when someone actually does the testing to back up their theories. I was going to say something about adding a lip to the vent to to increase the effect, but didn't want to get too long winded. Excellent explanation and tips for testing, thanks

HIGHPSI4 said:

What you seem to fail to realize is that hood vents, unless engineered, do not work to cool the engine bay. The same principle that allows airplanes to fly will push air from the hood into the engine bay and thus reduce the volume of air moving through the radiator which will make the engine over heat.

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Sorry, I fail to see that. Fast moving fluids ALWAYS have a lower pressure. I'm sure the vert guys experience it every time they drive - the shit will always pop out, not get pushed in by the air.

And what I am talking about is actually the localized low pressure zone creating by adding a lip to a rear facing hood scoop.

Homemade Hood vents usually cause under the hood turbulance.. which is usually.. no always bad

99gst_racer said:

I was curious to see how much weight could be removed from the stock hood. I cut that bracing out last month to see if it would make a difference. It's wasn't much. The bracing only weighed about 4-5 lbs.

Most of the hood's weight is in the bracing along the perimeter of the underside - that bracing is along the hood's main support, so it's not something that you could safely remove. removing the bracing in the middle didn't really compromise the hood structural integrity, but you definitely can't use it an a table anymore.


FYI: My hood is for an "off-road only" 1G. I don't drive it on public roads. Also, 5 lbs may not sound like much, but if you can pull 5 lbs from ten different places, then you're making progress. It all adds up.

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I'm thinking about doing that to my 1GA hood. I have it off for painting right now, so I thought it might be a good time. How difficult was it? Could I do it with an angle grinder and a few cutting discs? Would it still be safe to drive on the street?

Thanks!

I know this thread is old but I thought that it was a good place to post this info. I have a 1Ga track car and I wanted to pull out some weight plus make some extra room in the engine bay for an A2W CAC. I cut out the skeleton with a cutoff wheel. Only took 2-2.5 hours. The top part of the hood is formed over the skeleton bottom part and then crimped at the edges and sealed. It may look like it is glued together and that you can “burn it out” but you can’t. Then you just need to take a screwdriver and separate the support structure from the top hood portion, there are about 20 glue spots.

Weights:
Stock Hood: 39.9 pounds
Rear Hood Hinge: 0.8 pounds each

“Lightened” Stock Hood: 25.7 pounds
Hood Pins: 0.15 pounds for both

So it saves you ~15.7 pounds plus frees up some space in the engine bay for free basically (hood pin set is like $10 on jegs). Granted the Hood doesn’t weigh 8 pounds like I’ve seen quoted online for a VIS carbon fiber hood but it also cost $10 vs $800, .

Bill

Not too bad. Although, I have a cf hood one the way that was $560 shipped so hopefully it's good quality.

99gst_racer said:

I was curious to see how much weight could be removed from the stock hood. I cut that bracing out last month to see if it would make a difference. It's wasn't much. The bracing only weighed about 4-5 lbs.

Most of the hood's weight is in the bracing along the perimeter of the underside - that bracing is along the hood's main support, so it's not something that you could safely remove. removing the bracing in the middle didn't really compromise the hood structural integrity, but you definitely can't use it an a table anymore.


FYI: My hood is for an "off-road only" 1G. I don't drive it on public roads. Also, 5 lbs may not sound like much, but if you can pull 5 lbs from ten different places, then you're making progress. It all adds up.

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That's awesome!