Drag Coefficient for 1972 914/4? |
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
Drag Coefficient for 1972 914/4? |
swatteam2 |
May 17 2006, 12:44 AM
Post
#1
|
Newbie Group: Members Posts: 2 Joined: 16-May 06 From: California Member No.: 6,014 |
Hey Everybody,
My name is Mike and doing an aerodynamics research project at the University of California, San Diego on an advisor's 1972 Porsche 914, involving CFD flow analysis, 1/18 scale model testing in the water tunnel with various aero configurations, as well as full-size coastdown drag testing with those same configurations, etc. My question is - are there any published values for the drag coefficient of this car? I've done a forum search and seen some estimates of .45, although the number seems to have been contested by others. Any help on this would be much appreciated! Thanks, -Mike |
Brad Roberts |
May 17 2006, 12:57 AM
Post
#2
|
914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
COOL. Can I come and watch? I live 10min from the school.
Andy has the "Das Grosse" book with all the factory info in German. Let me call him real quick. |
So.Cal.914 |
May 17 2006, 12:58 AM
Post
#3
|
"...And it has a front trunk too." Group: Members Posts: 6,588 Joined: 15-February 04 From: Low Desert, CA./ Hills of N.J. Member No.: 1,658 Region Association: None |
These are static tests? Reason I ask is my car will drop in the front about 1 1/4" to 1 1/2" at about 90 to 100 mph. I believe this would change those figures. Others have their cars even lower to start with than mine.
Observation. (IMG:style_emoticons/default/smoke.gif) |
Brad Roberts |
May 17 2006, 12:59 AM
Post
#4
|
914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
72 914: 0.37 73 is 0.38
B |
SirAndy |
May 17 2006, 01:00 AM
Post
#5
|
Resident German Group: Admin Posts: 41,815 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
brad is correct ... (IMG:style_emoticons/default/happy11.gif)
(IMG:style_emoticons/default/beerchug.gif) Andy Attached image(s) |
Joe Ricard |
May 17 2006, 05:08 AM
Post
#6
|
CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
And I imagine any of the other stuff that gets added will drastically effect Cd.
I know the cow catcher air dam and little flippy tail fin slowed the car down quite a bit on top end. Like 10 MPH I normally run the early wrap under valance and slick trunk lid. windows up. |
type47 |
May 17 2006, 05:38 AM
Post
#7
|
Viermeister Group: Members Posts: 4,254 Joined: 7-August 03 From: Vienna, VA Member No.: 994 Region Association: MidAtlantic Region |
i've seen a C chart with different values for lights up, top off, windows up, etc.
|
jd66921 |
May 17 2006, 09:13 AM
Post
#8
|
Member Group: Members Posts: 316 Joined: 9-January 06 From: Texas Member No.: 5,394 |
i've seen a C chart with different values for lights up, top off, windows up, etc. 914_Cd.htm ( 762bytes ) Number of downloads: 184 |
URY914 |
May 17 2006, 09:18 AM
Post
#9
|
I built the lightest 914 in the history of mankind. Group: Members Posts: 123,027 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
72 914: 0.37 73 is 0.38 B Must be the tits on the front bumper? I wouldn't think they would make that much diff. (IMG:style_emoticons/default/confused24.gif) |
Chris Pincetich |
May 17 2006, 10:16 AM
Post
#10
|
B-) Group: Members Posts: 2,082 Joined: 3-October 05 From: Point Reyes Station, CA Member No.: 4,907 Region Association: Northern California |
Mike- cool project!
No doubt aero efficiency is a major player in gas milleage and top speed, 2 things we all want to improve. If you have any wiggle room in testing the areo efficiency of different 914 mods, I think we would all be interested in more info on the effects of GT flares, rear spoiler/ducktail, stock front air dam vs. LE air dam, lifting the back of the roof, and maybe smoothing out the area under the exhaust/muffler. Try the "Search" feature in the upper right of the page - lots of 914 mods out there. One really good thread on aero improvements could probably be found by searching "lift and roof"...there are some vortex generator tabs that were attached tot he rear edge of the roof that MIGHT be making a signifcant improvement. (IMG:style_emoticons/default/beerchug.gif) |
MattR |
May 17 2006, 10:21 AM
Post
#11
|
Advanced Member Group: Members Posts: 3,279 Joined: 23-January 04 From: SF Bay Area Member No.: 1,589 Region Association: Northern California |
Are you in FSAE down at UCSD?
|
Joe Ricard |
May 17 2006, 10:47 AM
Post
#12
|
CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
What ever happened to the guy with air tabs on his race car? Was there any benefit from it?
|
SirAndy |
May 17 2006, 10:54 AM
Post
#13
|
Resident German Group: Admin Posts: 41,815 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
more info on the effects of GT flares pretty good for a shoebox with wheels ... (IMG:style_emoticons/default/rolleyes.gif) Andy |
swatteam2 |
May 17 2006, 01:48 PM
Post
#14
|
Newbie Group: Members Posts: 2 Joined: 16-May 06 From: California Member No.: 6,014 |
Hey, thanks everybody for your responses! For our project, we'll be testing various combinations of the following modifications (both scale model and full-size) - top on/off, windows up/down, an air dam, and 2 sizes of rear spoilers. Unfortunately since our project timespan is only 10 weeks, we'll have to restrict our tests to these modifications and probably won't be able to look into other things like fender flares, etc.
Basically we'll be doing comparative drag testing in the water tunnel (already have previously collected data on lift-coefficient effects of these mods). The water tunnel has a flow velocity limited to about 2 m/s which means that for a 1/18 scale model, we'll only be able to achieve a scaled speed of a few miles per hour. The published values that you have given me will help a lot in seeing if testing at such scaled speeds will still yield reasonable estimates of Cd. We'll also be doing flow-visualization in the water tunnel using dye lines to validate the CFD flow analysis results and observe any salient aero effects of the various mods. As far as real car testing, we'll probably head over to the scripp's ranch area (some nice flat stretches of road) for roll down testing to see if the drag trends observed in CFD and water tunnel testing for the various configurations are reproduced in real life. We most likely won't be able to get accurate estimates of the true Cd in this method since it would be difficult to determine the rolling resistance of the car at the speeds tested, but we should at least be able to get comparative values. Any ideas on how we could accurately estimate the rolling resistance at around 70 or 80 mph would be welcome! Thanks again for all your help, I'll keep in touch! -Mike |
Joe Ricard |
May 17 2006, 02:07 PM
Post
#15
|
CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
Alot of variables in rolling resistance too.
Tire width and compound. Air pressure in tires Bearing adjustment. Brake rotor trueness (pads can drag on warped rotors). Speacially on the back. |
TonyAKAVW |
May 17 2006, 02:45 PM
Post
#16
|
That's my ride. Group: Members Posts: 2,151 Joined: 17-January 03 From: Redondo Beach, CA Member No.: 166 Region Association: None |
QUOTE Mike and doing an aerodynamics research project at the University of California, San Diego Go Tritons! -Tony (EE c/o 2000) |
newto914s |
May 17 2006, 04:05 PM
Post
#17
|
Senior Member Group: Members Posts: 561 Joined: 16-February 04 From: Thornton, CO Member No.: 1,663 |
72 914: 0.37 73 is 0.38 B Must be the tits on the front bumper? I wouldn't think they would make that much diff. (IMG:style_emoticons/default/confused24.gif) You ever watch "Baywatch." tits slow thinks down a lot (IMG:style_emoticons/default/boldblue.gif) But I'm not complaning |
Al Meredith |
May 18 2006, 06:03 AM
Post
#18
|
Senior Member Group: Members Posts: 967 Joined: 4-November 04 From: Atlanta, ga Member No.: 3,061 |
I knew I had this old PANO took a while to find it. I have no way to scan the article , but if someone goes to Panorama May 1978 there is a great article about Weissach Engineering. There are pages of graphs showing everything from "lift at ther rear wheels at differing speeds with and without spoilers : to: CD of a 914 in all configurations. As stated before .363 closed up, .380 lamps up, .381 lamps down windows open, .389 lamps down windows up and roof off, .447 windows open and roof off lights down, .464 all dirtyed up (windows open roof off and lights up.
If someone has May 78 please scan ....good info Al |
ryap |
Oct 11 2006, 04:41 PM
Post
#19
|
Newbie Group: Members Posts: 7 Joined: 19-July 06 From: Los Angeles Member No.: 6,465 |
All the drag coefficient info is nice to have, but it doesn't do you any good unless you know the reference area! Anybody know what that is? I assume it is the projected frontal area. Difficult to measure without a planometer. My rough guess is 23 sq. ft.
|
Borderline |
Oct 11 2006, 05:27 PM
Post
#20
|
Senior Member Group: Members Posts: 720 Joined: 8-February 05 From: San Juan Bautista, CA Member No.: 3,577 Region Association: Northern California |
the guy who had the vortex generators was Greg (race914) Braun. I met him at Laguna Seca a few weeks ago. He told me that he really likes the vortex generators. He liked them so much he put a bunch on the back of his trailer to improve gas mileage!! (IMG:style_emoticons/default/biggrin.gif)
|
Lo-Fi Version | Time is now: 27th September 2024 - 10:16 AM |
All rights reserved 914World.com © since 2002 |
914World.com is the fastest growing online 914 community! We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ... |