Some interesting pressure test readings

[verticalflight]

I recently purchased a Magnehelic gauge to measure air pressure on various parts of my 964 with RWB bodykit.

Read more here and here.

Below are pics of the unit and how we routed hose to do the measurements. Note I have a radiator now in the front, which dumps air below the car. I am looking at ways to route the air differently so as to not create lift in the front.

Here are my readings: (all at 50 mph)

FRONT BUMPER
- In front of the bumper, 1.0
- Inside the radiator exit below the car 0.9
- At the radiator exit below the car 0.85
- Car stopped, fans only, at exit 0.2

FRONT FENDERS
- Outside of fender exposed to outside air flow 0.1
- Edge of fender 0.4
- Just inside fender 0.45
- Inside fender nearish bottom front 0.5
- Insider fender, at bottom of front bumper 0.3

FRONT/TRUNK
- On hood, front -0.4
- On hood, center -0.8
- On hood, near windshield 0.75

DECKLID
- Front of grille 0.55
- Past the grille 0.85

Things that made sense to me:

- It looks like most of the air coming through front bumper is going out the air exit under the car past the radiator (1.0 -> 0.85)
- Pressure past the decklid suggests the grille is an exit, this makes sense as in my car the intake is actually in the backseat.

Things that surprised me:

- There is way more air pressure inside the fenders than expected(air from the ground?)
- Interesting how the pressure changes along the hood from negative to positive.

[fanaudical]

Interesting.

Question: What are you using for reference pressure? Just leaving the low port of the magnehilic open inside the vehicle?

[verticalflight]

Yes, setting the calibration at zero with no flow and then set a speed to 50mph so that the highest reading (front of bumper) was at 1.0...

[Trakrat]

Why are you even doing this?

[jnberry]

Did you test the rear quarter NACA ducts?

[aston@ultrasw.c]

Originally Posted by verticalflight

FRONT BUMPER
- In front of the bumper, 1.0

FRONT/TRUNK
- On hood, front -0.4
- On hood, center -0.8

Great data!

Especially as it supports my guesstimate of front end airflow

[verticalflight]

Why not do this! Actually just want to understand how air flows around the car and ways to think about cooling, dumping the radiator air, etc.

Didn't measure the NACA ducts but I bet they work flawlessly as the throttle body is cool to touch when before the air intake was inside the engine compartment it was getting very hot. There is a cool induction sound too along with the beastly noises from the motor...

[3rd_gear_Ted]

Great effort at bringing data to the forum.
Would love to see data about front dive planes.
Read this months Panarama magazine about the 962 aero findings discovered by Porsche.
Like the engine air intake setup.

[ChrisBennet]

I played around with something like this a decade of so ago using a sensitive digital manometer. I was trying to measure the pressure difference/drop across the stock fender radiator. In my experiments I did not see any difference in pressure. :-(

I think I also tried measuring the pressure in from the front spoiler. You may have inspired me to revisit my experiments.

I put foam around the end of the hose to avoid a venturi effect from producing a lower pressure.

[aston@ultrasw.c]

Just reviving an old thread to see if anyone has additional data.

Or, you can show off your latest hood venting project.

[Tippy]

This is awesome data. Interesting stuff to compare.

[chrismorse]

Hi VF,

Where did you get the gauge?
I would like to measure engine compartment air pressure with and without a duck tail in an attempt to quantify reports of engine temp reduction with the duck.
Not sure how conclusive the test will be, particularly since the car has two thermostatically controlled coolers.
Wouldn't power also be proportional to air pressure?
Perhaps a with and without duck timed 4th gear pull from 40 to 80 would be a better indicator of power differential. Not expecting much, but if the substantial majority of before and after duck reports indicate noticeable, albeit small, temp reductions, I think there will be some hp there
Dad's old stock 74 only has 150 hp ��
Chris

IIRC, the aerodynamic effect is a square of speed function and would be more substantial and measurable at 100 or 130, but I don't have anyplace to test without risking the red and blue lights.

[verticalflight]

Chris, I got it used off eBay for cheap like $40

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311.R1.TR9.TRC2.A0.H0.Xmag nehelic.TRS0&_nkw=magnehelic+gauge&_sacat=0

You want one that can go to 1" I think so its not overly sensitive...

BTW the readings are all relative, not absolute values...