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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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lapuwali |
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#2
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Not another one! ![]() ![]() ![]() ![]() Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 ![]() ![]() |
QUOTE I'm sure of the units, but the reference point is probably not at atmospheric pressure. The numbers can't tell you what pressure is at a certain place, only the difference in pressure between measured points. But the numbers seem at least 10x too low. I just can't swallow 65mph against the front bumper only generating a 0.06psi increase in pressure. Either the pressure in the ashtray was changing a lot more with speed than I'd think it would, or something else is wrong. I wonder if the foam threw off the results? I think I'll build something using a MAP sensor that reads above 1 bar. I'm pretty sure I have an MPX250 in the Megasquirt kit I've not assembled, which should be 2.5bar absolute, or 1.5bar above atmospheric. |
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