944obscene

The valence, at the very least, would smooth out airflow, which is what I was assuming. It's not in a possition to create downforce, but much like other aerodynamic parts, it will help direct airflow behind the car, which will reduce drag and turbulence.

Lemming

"what is behind me does not matter"


None on the passenger side and a small circular convex mirror mounted on the role bar on the driver's side (barely sticks out of the window). On the inside I have a large 17" convex. The system works really well, I can see 90 degrees out each side and behind me without moving my head. You do of course have to get used to the distortion from the convex mirrors.

Van

Yeah, I have that large longacre mirror in my car, but I have the door mirrors, too.
I imagine you see a pretty good aerodynamic gain from removing the mirrors.

Lemming

With a full containment seat, R3 H&N, and being height challenged, I cannot turn my head far enough to the right to see the passenger mirror. I'm pretty sure it doesn't hurt the aero as well, especially running the billboards

ritzblitz

Lemming, that's similar to what I wanted to do.

I've been at school so much and havent had any time to do much, but I still plan to run an aluminum skirt along with a small splitter for track days.

I dont think a vortex generator is necessary on a 944, but it is a good thought. On an evo, yes, its a 4 door sedan with a high roofline. Our cars not so much.

As for smoothing out airflow under the car- smoother, less turbulent flow creates more of a pressure differential, therefore increasing the "suction", if you will. So that is basically downforce. But, I couldn't see a 951 valence doing a whole lot, just speaking on principle.

paulmezz

Lemming,

What kind of lift is that in the picture?

This kind?
http://www.harborfreight.com/cpi/cta...emnumber=91315

I've been lift pondering for a while now.. Ok, back on topic

Lemming

Bendpac scissor lift.

944obscene

Necessary is a relative term. I don't think a big turbo is necessary, but that's not to say it isn't desirable. Or that there aren't benefits worth arguing over. Just hear me out on this. So that I have said my peace.

As the car moves faster, the pocket of negative air pressure trailing behind it will increase in size. By how much, I do not know, but I do know that at 120mph or 140mph, everything WILL count. I could only speculate on the effectiveness of Vortex Generators. Especially placed at any point on the surface of the 944. But think of the use of VG's in aviation... The birthplace of the instruments.

On a wing, which has less surface variation, than even the hatch of the 944 itself, VG's can mean the difference in a stall, or superior air-handling. With this considered, think about how the air pocket increases behind a 944 during a pull down a back straight At say... road America. Or even Hallett. As that pocket gets bigger, it creates a larger and larger suction on the car (pulling on it and reducing the effectiveness of any spoilers). Reducing this pocket will do as I mentioned before: Reduce the suction on the car, and allow for better use of any devices creating downforce on the back of the car.

I'm no fluid dynamics expert, but I'm pretty sure I'm at least ROUNDING the head of the nail. Just like a gurney flap, the VG's are small, but have been proven to work... Even at slower speeds. To know their effectiveness, you either need to know a lot of math, or have experience with your car and test them yourself to see AND recognize any differences. I obviously couldn't test this, because I don't have any seat time in my car on a track yet. My assumptions would be skewed and biased.

As for the rear valence, I think it also helps with what happens BEHIND the car, more than UNDER it. Being at the trailing edge of the vehicle, the air sweeping around it is being channeled and smoothed out. This allows it to fill the void behind the car, that I was talking about earlier. If this is true, and my assumptions are correct, then even an NA 944 would benefit from reduced aerodynamic suction. Nevertheless, an assumption at this point.

And I question the effectiveness of the VG design, used on the EVO's, as that design looks more like protruding shark's teeth, rather than an actual vortex generating tool. The idea is to have a more or less flat edge, perpendicular to the surface it is mated to, and canted to the side so that air tumbles over the top of the generator, and spirals down the surface of the wing, or in this case, the car. Thus creating a laminate barrier over the back of the car and ultimately putting more pressure over the rear spoiler as well as leaving less of a pocket of turbulent air behind said car. If done right, the air flow should look something like this:




The Generators are placed just at or after the highpoint of the surface they are being used on, to help pull the air closer to that surface, where suction and turbulence would normally occur. I assume, that a visual test could be done by taping short pieces of string (inch or so long) to the hatch glass and watching how they act before and after... This is if someone wanted to test the idea. My car doesn't run right now lol. Oh well.

Here is an aviation article attesting to the effectiveness of the VG tool. Read between the lines. I understand that we're not concerned about the AOA of our car lol. I'm just stating that there are other advantages within and resulting from those that this man talks about.

http://www.avweb.com/news/reviews/182564-1.html

ritzblitz

I understand how they work, I was trying to compare our cars with an evo. Airflow over the roofline of an evo more or less totally delaminates at the end of the roof. Just assuming that since our cars are much more streamlined in design, I don't think the effects of a VG would be as significant as on a sedan.

Air doesn't always have to delaminate at some point along a body. Just a thought. But, I guess a VG on a 944 could have some effect. We just need to find out if the airflow over the car is laminar or not.

I haven't read through this whole thing, but it is an awesome technical analysis, although it is on an evo. They address the shape and size of the VGs and why they are optimal.
http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

I agree with you on the rear valence. It probably helps aid in creating the effect of "lengthening" the body, therefore reducing drag.

944obscene

I do believe that the airflow over the rear does not stay laminate. I'm going to tape a bunch of strings on the hatch and video the results after I get my car back up. Different speeds and different situations. This will show whether or not any form of air control is needed. I'm going to lean towards yes for now though. Somehow, I just don't think the air is that stable over the back...

ritzblitz

I agree, it probably cant be perfectly stable. Definitely let us know how that works out.

I assume you have seen what Jack Olsen did with his 911 aero project?

944obscene

I have not. Link?

I observed an engineer on another automotive forum do an aerodynamic test with strakes and VG's for the purposes of directing air into some vents on the side of a car. You'd be surprised what those little pieces of string will reveal.