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bondo |
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Practicing my perpendicular parking ![]() ![]() ![]() ![]() Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California ![]() |
With the help of my lovely wife, I have made the air pressure measurements on my 914 at speed. The reference point was the ashtray in the dash. The ends of both hoses were buried in the center of 2" blocks of open cell foam to prevent air movement from affecting the pressure readings. I realize the reference point is not going to be at exactly zero, but as a reference it will show pressure diffrences between different parts of the car. The windows were rolled up, and the targa top was on. Here are the numbers, in kilopascals:
at 45 MPH front center of front bumper: 0.21 middle top of front trunk lid: 0.03 inside front of front wheel well: 0.00 middle top of roll bar: -0.03 middle of rear window: -0.03 inside engine compartment (coasting at idle): -0.01 inside rear wheel well: 0.02 at 65 MPH front center of front bumper: 0.44 middle top of front trunk lid: 0.02 inside front of front wheel well: 0.01 middle top of roll bar: -0.05 middle of rear window: -0.04 inside engine compartment (coasting at idle): -0.03 inside rear wheel well: 0.03 After our last measurement, we rolled down the driver's side window and drove at 45 MPH to see what difference that made on the reference point. The rear wheel well measurement went up from 0.02 to 0.07, which means that at 45 MPH the pressure at the ashtray is 0.05 kPa lower with the driver's side window down. Whelp, there's my little numerical contribution to the 914 community. --Royce |
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maf914 |
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#2
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Not a Guru! ![]() ![]() ![]() ![]() Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None ![]() ![]() |
It would be interesting to know the pressure under the car at these speeds. The relative pressure between the engine bay and the underside of the car affects the cooling fan volume.
Smoothing the bottom to reduce drag also increases air velocity and reduces pressure. Modern performance cars attempt to do this. And of course racing cars dsigners go to great lengths to tune the underbody for maximum downforce from either flat bottom or venturi designs. The bottom of a 914 is fairly rough so I would guess flow is probably turbulent and pressureis higher relative to the engine bay. Just a guess! |
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