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jj
jj HalfDork
1/30/19 5:17 p.m.

I have been planning for some time now to add hood and fender vents to both cool better and lower pressures under the body panels. 

I wanted to share a method I found for measuring low pressure points that is very easy and could be done with materials laying around. If something is off it’s because I am not an expert and cobbled this idea together. 

So I built a simple manometer using tubing and colored water. Material I used: Clear tubing, 20 ft. Food coloring. An old board. Tape. And a ruler. 

Here are pictures of the set up. 

In car

jj
jj HalfDork
1/30/19 5:25 p.m.

Testing:

i used the same stretch of road. Always took my reading at the same spot on the road, at the same speed and going the same direction. 

One end of the tube was in the car taped to the window, windows up. The other end was taped to the body at right angles to the wind. Here is how the outside tube was set up. 

The baseline measurement on the  ruler was 6 3/8 inches. This was measured not moving, on level road with both tubes inside.

Picture of the most vacuum I measured. 

jj
jj HalfDork
1/30/19 5:36 p.m.

Results:

the way it is set up, higher numbers on the ruler means vacuum, while lower means positive pressure. 

I taped out areas of hood and fenders to test and wrote the measurements on the tape, comparing to the baseline of 6 3/8. 

Here is what I came up with. 

Out of curiosity I also measure the point at the base of the windshield that people always say is high pressure. It was but only just barely by a 1/16 inch. 

I also measured the center of the deck lid with and without a the factory spoiler. The deck lid was positive pressure by a small amount (1/4”) and even without the spoiler by (1/8”). I expect the latter because the trunk lid curves up a small amount in the back. 

Dave M
Dave M Reader
1/30/19 5:40 p.m.

This is awesome and truly grassroots, thanks for sharing! I wonder how much it costs to model this with a commercial software package? Probably a lot.

jj
jj HalfDork
1/30/19 5:52 p.m.

In reply to Dave M :

Thanks. Cost was my main factor and I was trying to find a way to not buy a gauge. I hope to also use it to test a splitter and a spoiler with and without gurney flap. 

iceracer
iceracer UltimaDork
1/30/19 6:41 p.m.

I made one of those years ago.    I didn't use it a lot and I don't know what became of it.

Robbie
Robbie UltimaDork
6/3/19 1:43 p.m.
jj said:

In reply to Dave M :

Thanks. Cost was my main factor and I was trying to find a way to not buy a gauge. I hope to also use it to test a splitter and a spoiler with and without gurney flap. 

Have you tested said spoiler and splitter yet? I'm interested to see what you do.

jj
jj HalfDork
6/3/19 5:49 p.m.

In reply to Robbie :

I haven't actually other that watching that pressure increases with speed on the trunk lid using an 8" spoiler.  The car is actually up for sale now as life changes.  But this testing process is very easy to do.

malibuguy
malibuguy Reader
7/6/19 10:42 p.m.

i bought a used Dwyer Magnehelic pressure differential gauge MANY years ago to test intakes and aero with.

Never berkeleying used it once LOL  I really should

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