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Old 02-21-2012, 12:30 PM   #1
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Default Hood lifting under pressure

I recently did some work around the radiator and had the belly pan removed. Since its cold right now I have left it off for the last two weeks.

Driving to work this morning, I noticed that the driver's side of the hood appeared to be lifted about 1/4"-5/16" above the edge of the fender where it will isually sit flush with the fendor. My first thought was that I had not pushed the hood all the way down when I checked the oil yesterday. Scary when you are doing 75-79mph down the interstate. I stopped at my exit and noticed that the hood dropped back down before I even got out of the car to check. It was latched properly and my hinges weren't sticking (I have that problem on my 97 and the hood will stick up if you don't push it down at the hinges).

So back to my point. It appears that removing the belly pan causes enough of a pressure increase under the hood that I could see lift in the hood itself. I have also noticed over the last two weeks that the front end feels more twitchy at speed, especially with any crosswind.

So, does the removal of the belly pan really affect the under hood pressures that much, or a I just seeing things? I bought a magnahelic gauge (up to 2" H2O) two yeas ago to do some testing of hood pressures (sure you have seen the hood pictures with pressures recorded), underhood pressures and delta P's accross the radiator and intercooler for different configurations. It would be interesting to see how the delta P changes accross the radiator with/without shourding, ducting, sealing, air dam, belly pan and hood louvers. I am only NA at this point and track it this way. I have been collecting the turbo parts for a few years and am about ready to take the plunge. I would just like to have issues like this optimized before I add the turbo.

I have not been able to find any info related to measured pressures accross the radiator, intercooler or inside the engine compartment, only stuff related to above hood pressures for the purpose of locating scoops or louvers.
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Old 02-21-2012, 12:33 PM   #2
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I did said testing and found that with the fans off and no belly pan, it seems that some air reverses through a portion of the radiator.
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Old 02-21-2012, 12:41 PM   #3
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Yes, it affects under-hood pressure. The entire purpose of the bellypan is to prevent the high-pressure air under the nose of the car from entering the engine compartment and reducing/reversing the pressure delta across the radiator.
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Old 02-21-2012, 12:46 PM   #4
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I knew it affected it enough to reduce radiator efficiency, but didn't quite think it was enough to lift the hood.
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Old 02-21-2012, 01:20 PM   #5
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My daily lifts like crazy and it has the pan. My track car hood does not lift at all with the vent, like a bauce.
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Old 02-21-2012, 04:44 PM   #6
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Popping your NA headlights is another good way to get the hood to lift.
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