+1 i saw an independent wind tunnel test of an early 308gtb, if memory serves it was something in the order of .36 i believe which was still outstanding for its day. i recall porsche was really proud of .36 with the then new 924 and even featured it in their ads. wind tunnels much like dyno's will have have different reading from each others. basically they dont all read the same. anyhow they did also tested a mid 70s 911 along with the 308 at this tunnel. much to my surprise the 911 with a much taller profile and bugeye exposed headlamps was prettly close in Cd and Cda to the sleek profile 308 . however the axle lift were much worse on more dated design.
Mine is painted fiberglass (car build date is Sept. '84 - Euro QV)... True to Ferrari form, they probably did the first ones in vetroresina then moved to steel!!
Cd varies with velocity. And bear in mind that a low cd isn't the be all and end all. You have to factor in the frontal area for one. And in a sports car, you have to have decent downforce else your car will take off or flip. It all ends up being a compromise. A modern F1 car has a cd of 0.7 to 0.9, up to as much as 1.1 depending on the circuit. Go figure.
No, was looking at the links Glen posted. The under-tray looks too boxy, the lower clip is flush with the front bumper, and the nose seems to have an front air dam like the 328. I just wonder how much time would be needed to dial in the correct measurements or if there is someone who has already done this. Also how difficult would it be to make adjustments to the CAD car? I have the euro bumper on mine and it is pushed back. Originally Posted by glenv6 View Post 308 STL file available here for $100.00 USD (or free if you have an STL to upload): http://www.3dcadbrowser.com/preview.aspx?modelcode=7616 http://www.3dcadbrowser.com/preview....odelcode=23789 Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
i dont know what velocity it was tested at. but there were various cars tested at the same time in the same tunnel. much like running on the same dyno on the same day will give a better comparisons between vehicles regardless what the actual number were. Cd A is the coefficient of drag x frontal area as i already mention. this combine with rolling friction is operating resistance. axle lift is reverse of downforce you are speaking of (most street cars produced lift in the 70's as I can remember). do you actually think a stock 308 made downforce? still i cant see any stock 308 remotely come close to flipping at top speed. im no areo expert even though ive operated automotive wind tunnel and watch an Forumla car test at Swift in San Clement (btw they did use to do F1 Tyrells there). It pretty obvious modern F1 cars are high drag vehicles, hence there relatively low top speed for power output. to put things in perspective, ive come to understand a modern F1 lets off the throttle at high speeds the aerodynamic drag / down force will "airbrake" car at over 1.5 G. its hard to believe but its braking much harder than a 308 without even touching the brakes! sorry if i didnt make myself clearer with the previous post. cheers hf
I suppose not to difficult but I have no CADsoftware to manipulate the images with. There are others here that do at work. However the pro's don't deem this as worthy I am afraid.
I just tried loading the test image from the 3D Cad Browser website into the free Autodesk Falcon software. The results were not great. Falcon rendered the general shape of the object ("lcd tv") but not the "texture" detail. So I don't think Falcon is powerful enough to fully render the image in a way that is useful, at least for what I want to see. I think the general shape provided by the cad files on the 3D Cad Browser website will work to see air flowing over the windshield then over and through the spoiler. Getting a visual of what this thing does will satisfy my curiosity. Unfortunately I don't think the free software I found will provide the resolution required to see the details. I'll keep searching...
Here's one!... http://www.ebay.com/itm/REVELL-1-24-T-V-SHOW-MAGNUM-P-I-308-GTS-FERRARI-CAR-KIT-NEW-/110819438830?pt=LH_DefaultDomain_0&hash=item19cd5a70ee
I have spent quite a bit of time in various wind tunnels in Europe. The conventional testing speed was 140 km/h for passenger cars (the published figures). Most of the cars I have seen reached their lowest Cd around that sort of speed; it's slightly higher at lower speed (flow not following cleanly), and tends to increase with increased speed up to a point where the airflow breaks down and the car hits an "aerodynamic wall". A do not believe that a stock 308 creates downforce: to my knowledge, the Testarossa was the first production car to generate negative lift coefficients front and rear.
That model seems very rough. Small (full size) details like the actual values of the front corner and rear spoiler radii have a major influence on drag. And so have parasite flows throughout the body via shut lines etc. Unless you correctly model the underside of the car incl. wheel wells, suspension, wheels with their correct rim openings and tire sections, engine bay, radiators, the correct air intakes/exits, and mirrors, your simulations are going to be irrelevant. The airflow through the engine bay has a major influence on the rear lift and flow over the roof. What ever the reasons for the addition of the roof spoilers were, I can's see why it would not affect the airflow over the car and through the engine bay.
I would actually like to build a front splitter and a rear diffuser to see if it would fix the lift problem at 130 mph. Using the wind tunnel software could save time by testing on the PC.
I doubt that you can get any reasonably accurate result with a PC. If that was possible, the car companies wouldn't invest that much money in real tunnels to back up their extensive calculations on mainframe systems. Cars are very complex aerodynamically due to the ground effects and the spinning wheels... But worth a try anyway to see what the results are - keep us posted!
I wouldn't have believed that a thread about the roof spoiler could have lasted that long, and brought us so much interesting information. The roof spoiler on my '89 GTS is smooth and painted body-color, as ordered. It seems to be fiberglass.
I think a much better approach to resolve this is to abandon attempts at computer simulations and try a real life test. Not necessarily with a wind tunnel. Difference in Cd can be ascertained with a coast down test. You'd need two identical cars (weight, mirrors, front spoilers etc) filled to the same level and with the same tyres at the same pressure. On a wind-free day. One with spoiler and one without. Then do a few runs and calculate the average. To work out whether increased airflow hits the rear deck, take the same two cars with equally warm engines. Then attach temperature probes and/or wind meters to both at a number of places on the deck. On the same wind free day and with full cloud cover. Again, a few runs each time and take the average. A good thing to do on a cloudy show day. After all this effort it would be depressing to find a zero or negligible effect, but hey ho
To work out whether increased airflow hits the rear deck, take the same two cars with equally warm engines. Then attach temperature probes and/or wind meters to both at a number of places on the deck. On the same wind free day and with full cloud cover. Again, a few runs each time and take the average. A good thing to do on a cloudy show day. After all this effort it would be depressing to find a zero or negligible effect, but hey ho [/QUOTE] Vaccarella, I'm afraid it will have to wait; I don't know about the temperatures these days in the U.K, but here in France you would have to drive a lot of miles these days just to warm-up the engines...it has been freezing cold for a least ten days, without any cloud in the sky! Best
There was a Mythbusters about sending a Porker backwards to check if it had a better cd that way. They used a model in a wind tunnel and a tank of water. That was myth-busted itself with a really good layman's description of aerodynamics in a discussion on the Discovery channel's forum for the show. It's the last one here, by Glenn: http://community.discovery.com/eve/forums?a=tpc&s=6941912904&f=9401967776&m=88519010701&r=36119655801#36119655801
i wouldnt think a testarossa did either, i reckon it would be the 355 or 360 before there is anything significant
