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Old 08-02-2014, 10:57 PM
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Default Hood venting

I liked what Chris (vette427sbc) did on his hood vent, opening up the area above the radiator on his L88 hood. I'm thinking on doing something similar, right after I round up a little more courage to cut into the fiberglass. In the mean time I'm welding up a piece to deflect a portion of the radiator exit air (there's obviously not enough hood opening space to try to exhaust all of the radiator air out the hood). This picture is during the fitment process. I've since welded up some reinforcements to it, as I'm not sure what the air/wind force against this piece is going to be.

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Haven't decided whether to bend the panels in a vee shape to follow the contour of the scoop, or to leave it straight and just let the hot air dump into the first bulge in front of the vent slots.

Last edited by 69427 : 08-03-2014 at 03:19 AM. Reason: Typo/spelling correction
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Old 08-03-2014, 10:57 AM
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Like this (XP819) hood?



Could be useful.
Cheers - Jim
Ahhh - had to do some more sleuthing to find your reference:
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Last edited by phantomjock : 08-03-2014 at 11:12 AM. Reason: add image vette427sbc
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Old 08-03-2014, 04:49 PM
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If it is not a sealed duct it may not flow out too well. If the under car pressure is lower it may want to flow down.
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Old 08-03-2014, 07:24 PM
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This is a topic dear to my heart. My 81 and I spent three years doing high speed 40 mile jaunts across the Mojave desert. We did a lot of thinking about cooling and airflow during the summer months and the GM guys had it mostly right the whole time. My Brit cars....not so much

The racer is where I started studying and experimenting with the underhood pressures as I was getting a lousy delta across the rad. decades later I do not overheat racing in the desert heat. So by extension, I maintain that no car should overheat if properly built. OK, That damned yellow Jag is still F..... with me but I think I know why

Point is, the engineers did it right to start with and if you're suffering now it's because the basics have been ignored. Clear the debris, explore the delta and ensure things are working as designed.....
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Old 08-03-2014, 07:38 PM
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Quote:
Originally Posted by GT6Steve View Post
This is a topic dear to my heart. My 81 and I spent three years doing high speed 40 mile jaunts across the Mojave desert. We did a lot of thinking about cooling and airflow during the summer months and the GM guys had it mostly right the whole time. My Brit cars....not so much

The racer is where I started studying and experimenting with the underhood pressures as I was getting a lousy delta across the rad. decades later I do not overheat racing in the desert heat. So by extension, I maintain that no car should overheat if properly built. OK, That damned yellow Jag is still F..... with me but I think I know why

Point is, the engineers did it right to start with and if you're suffering now it's because the basics have been ignored. Clear the debris, explore the delta and ensure things are working as designed.....
The engine doesn't overheat. Even with a 195 thermostat, 90+ degree track days, and the parking light grills blocked off. No basics have been ignored.
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Old 08-03-2014, 07:48 PM
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Quote:
Originally Posted by rtj View Post
If it is not a sealed duct it may not flow out too well. If the under car pressure is lower it may want to flow down.
I agree. I've got a differential pressure gauge (the top smaller one) to measure the points under and over the hood.

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I'm planning on trying some tufts also to get a visual look at the airflow, but with the frontend shape of a C3 I honestly can't imagine it having less pressure (at speed) under the hood than on top of the hood.
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Old 08-03-2014, 09:15 PM
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There ya go! The magnahelic tells the tale. Having that tuirned my racer around and it also confirmed the 81 was working right. Folks seem to tyhink the cooling is some kind of mag
Quote:
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Quote:
Originally Posted by rtj View Post
If it is not a sealed duct it may not flow out too well. If the under car pressure is lower it may want to flow down.
I agree. I've got a differential pressure gauge (the top smaller one) to measure the points under and over the hood.

[Only registered and activated users can see links. Click Here To Register...]

I'm planning on trying some tufts also to get a visual look at the airflow, but with the frontend shape of a C3 I honestly can't imagine it having less pressure (at speed) under the hood than on top of the hood.
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Old 08-03-2014, 10:24 PM
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Nice set up.
I wonder how many of us "aero-kooks" have a Magnehelic Gauge?
[should we ask for a show of hands?]
Just a few questions, if I may:
Are you using a multi-tube setup, and pulling "taps" or reset/retape after each run?
Have a recorder with you to take data?
Or, using a camera?

Just a few things I've been thinking about as I get closer.

Cheers - Jim
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Old 08-04-2014, 12:47 AM
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Quote:
Originally Posted by GT6Steve View Post
There ya go! The magnahelic tells the tale. Having that tuirned my racer around and it also confirmed the 81 was working right. Folks seem to tyhink the cooling is some kind of mag
Quote:
Originally Posted by 69427 View Post
Quote:
Originally Posted by rtj View Post
If it is not a sealed duct it may not flow out too well. If the under car pressure is lower it may want to flow down.
I agree. I've got a differential pressure gauge (the top smaller one) to measure the points under and over the hood.

[Only registered and activated users can see links. Click Here To Register...]

I'm planning on trying some tufts also to get a visual look at the airflow, but with the frontend shape of a C3 I honestly can't imagine it having less pressure (at speed) under the hood than on top of the hood.
This isn't a cooling thread. This is an underbody pressure/lift (reduction) thread.
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Old 08-04-2014, 01:07 AM
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Quote:
Originally Posted by phantomjock View Post
Nice set up.
I wonder how many of us "aero-kooks" have a Magnehelic Gauge?
[should we ask for a show of hands?]
Just a few questions, if I may:
Are you using a multi-tube setup, and pulling "taps" or reset/retape after each run?
Have a recorder with you to take data?
Or, using a camera?

Just a few things I've been thinking about as I get closer.

Cheers - Jim
I'm just a one man, low budget operation. I've got a couple of ten foot lengths of tubing (plugged into the Magnehelic) that I move around and tape onto body locations or plug into pressure/vacuum taps. No data recorder or anything, I just take a glance at the gauge(s) during the long straights on test & tune track days. Would be nice to have a printout of pressure versus speed or RPM, but I'm happy to just get whatever info I can however I can.
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