roman944

140mph? didn't know tow trucks could go that fast with freight!

V2Rocket

wowwww thats pretty cool.

just read up on it at wikipedia lol

apparently the guy got a bad lap time and decided to try the flap on, he got a bad time again but it turned out that it made so much rear downforce that the front of the car was lifting, causing major understeer.

ritzblitz

Yeah gurney flaps are a pretty cool little addition. A gurney flap would do something on a 968 wing.

I'm curious to know if they would work on a spoiler as well. I'll ask my dad (aerospace engineer) and get back to you guys.

BeerBurner

Please let me know. I've considered putting one on my Miata but I don't want to make things worse so I haven't done it.

BB.

CPR

Ritz,
Not sure if this helps but here is my take:
The implementation of front aero enhancements will mkae a difference in handling. The two basic types are the chin or lip spoiler and the air splitter. To understand the benefits you must understand the dynamics. The purpose of a true splitter is to "split" the air, hence the name. The point is to redirect the high pressure air flow up and over the car, (and thus onto the lip edge of your rear spolier creating greater rear bite/traction) while limiting high pressure air from forming/flowing underneath your car, which in turns creates "lift". It also helps "smooth" the air flow underneath the car, and in the case of the turbo, re-direct it through the lower rear valance which increases the cars stability...especially at high speeds.

A chin/lip spoiler is more of a cosmetic item, on these cars at least, as the nose/bumper is typically further forward than the lip spoiler. In other models where the lower lip is equal to or greater than the length of the bumper/nose it has a more noticeable impact. They do posses some split effect and ones that incorporate a belly, also provide some degree of air stabilization underneath.

The splitter shown in your sig car would be an effective example of what you would want to use.

ritzblitz

CPR, good information. Although, when I say lip I really mean air dam. What I constructed from rubber (for street, aluminum for track) is basically a vertical extension of the valence. I think its something like 2.5"-3" tall. I'm pretty sure it should have an effect, as the air dam limits the amount of air entering under the front of the car, therefore decreasing pressure, and increasing downforce.

I called my dad about the gurney flap. He wasn't 100% sure about the difference between it's effect on a spoiler vs an airfoil. Although, he did say that it would generate downforce on either application. So I guess for great results, incorporate it into a 968 wing.

I like this thread

Edit: another point I forgot- The nascar spoilers are kind of like giant angled gurney flaps. So i guess they work in that regard as well. I might try to fit one once I get back home. It has the potential to look sort of cool and be functional at the same time, although I'm not sure how I'd attach it.

M758

Keep it stock for now. It might help to some degree, but the 944 is naturally balance at all NA speeds. At speeds the NA can reach on the track downforce is not an issue and really you want to reduce drag to make up for the lack of hp. I have had my NA to 132 hp in a draft on the track and it is rock solid with no extra aero work.

Now may be it will help to some degree in certain places, but you would need to test that. So first get on track and make sure you are good enough as driver to feel the car and make sure the chassis is good and you have mechanical balance and grip. Then throw on aero tweak and see what happens.

CPR

Ritz,
Gotcha...just be careful. You do not want to eliminate all or in this case a majority of the airflow underneath. It will grant your car a different handling characteristic. Some restriction is ideal...but it is finding that balance. If this is a relatively straight downward extension, you may want to incorporate some type of lip or edge to help break up the flow. Otherwise the potential for the air to be trapped/unstable is relevant. The 2 most common results would be:
1. Causes an unpredictable/unstable handling due to erractic route of air flow (similiar to driving in a bad crosswind)
2. creates an undesirable aerodynamic front, causes slower speeds (noticeable predominantly only at higher 80+est) and uncertain cornering, typically a push.

As I stated these are just some common items that I came across in developing a splitter.

Either way, I applaud your efforts in this. It is not as easy as some think. Good Luck, and if I can be of any help send me an e-mail to:
cpracing_aero@live.com

PATRICK

Lorax

+1

My feeling is that with the low power of the NA reducing form drag is more important than downforce.

944obscene

I would think a 944 would benefit from a front air splitter and the rear splitter from a 951. A skid plate would help, if only to stabilize airflow underneath the vehicle. I want to do this now.

M758

The car stock has an undertray which I believe when used helps smooth the airflow under the car and reduces drag. Many NA undertrays have been lost over the years, but you can fab one pretty easily from sheet metal.

ritzblitz

My car still has the undertray. It's lowered as well.

Good stuff Pat.

Since my current project is just a trial fit/ street version out of rubber, I plan to run the car for a DE or 2 before adding an aluminum version of the dam and then possibly a splitter.

The thought of a small lip/protrusion around the bottom edge of the air dam is interesting. I was wondering why you think the air dam would tend to "push"? Wouldn't increasing the front downforce add to the possibility of oversteer? Although, I guess extra turbulent air underneath the front of the car could upset the balance and cause what you were saying about unstable cornering and such.

StoogeMoe

You need to be more concerned with mechanical grip and balance than with aero balance. At the speeds you will be doing at DE, the aero part will be negligible. You have precious few hp to expend trying to gain downforce. You're better off trying to eliminate drag instead of increasing it.

ideola

Haven't seen one of these for the 944, but here's the 924's pressure differential chart:


CD numbers (see the fourth table down):
http://www.mayfco.com/dragcd~1.htm

More Porsche CD numbers:
http://74.125.93.104/translate_c?hl=...em2y0gpj-aGA8A

It's notable that the 944S2 and 86 951 have a lower CD than the other 944s, although it's not clear what it's attributable to.

Reference material:
http://www.up22.com/Aerodynamics.htm

Autospeed also ran an excellent three-part series on Undertrays, Spoilers & Bonnet Vents, including describing a technique to determine results using magnahelic gauges:
http://autospeed.com/A_2159/cms/article.html
http://autospeed.com/A_2160/cms/article.html
http://autospeed.com/A_2162/cms/article.html

CPR

Well alot would depend on the actual design. The picture I have in my mind by your description is a flat piece extending straight down.

With that said, would this actually increase downforce? Or does it act like a giant air brake? Does it actually manipulate the air flow? Or does it plow it? These are the questions that would need to be answered.

As for the push, with a large flat surface typically the air is not channeled correctly to achieve greater down force. The resulting unequalised pressure tends to "upset" the front end and disturbs the underneath flow. If the unequal pressure at the nose is greater than the underneath turbulence then you should generate a push. If the undercar turbulence is greater than the unequalised frontal pressure you should become loose. The latter is due in fact to not only a high pressure build from underneath, but the erratic airflow that would accompany it.

As I said, I am just gauging this based on my mental picture of what was described. You could be building something totally different than what I am imagining.

Also, my comparisons are at higher rates of speed, where air flow and its' applied properties are more pronounced. Again, though, I applaud your efforts and creativity. If I can be of any help, just let me know.

And good luck with the project