Leigh2

Has anyone run across data that would quantify the down force available from the various Porsche body parts? For example the 996 series has multiple front bumper covers; 99-01, 99-01 aerokit, 02-04, GT3, GT2, turbo etc. I'm assuming the GT3 or the GT2 nose has the highest but did Porsche or anyone else actually measure how much? Same goes for the back end...wings etc.

Tom W

You can't get data that simple. The aero data will be very dependent upon the ride height, the rake that the car is set up with, what springs are being used, etc. I spent an hour or more last night going through the MoTeC data from my car and looking at what we need to change to improve the aero. An issue I'm trying to address is the 'squat' that you get when accelerating (going to WOT causes the rear to lower and the front to rise). This significantly changes the aero profile and the changes in down force that occur with increasing speed. It's one reason that a wind tunnel does not answer all questions.

va122

data? no. I tried that once with different wing angles with respect to lap times and straightaway speed. Useless.

What I think you're asking is how much more force does the RS nose add vs the stock GT3 nose. That i read as 20kg if you cant the radiator back and plug the holes underneath. I don't know what the RS wing vs non is but I wouldn't bet money on the answer for all the reasons tom mentioned. Waaay to many variables.

va122

easy answer is YES, the RS bits will give you more downforce (over 100mph) easily felt driven back to back.

Accelerator

Leigh2,

I read some data once concerning the stock 996tt and fr vs rear DF. As I recall
it was actual data from Porsche and showed that when running at 100mph (I think that was the number used) the front shows slight positive lift and the rear shows very little negative lift (downforce). Before I added DF to my car it did feel light in the front end at high speeds. I've not seen any data on any of the other configurations. Tom is absolutely right about data that would actually apply to your specific vehicle. The P data I suspect is relative to a totally stock setup; ride height tire spec, etc.

Tom W,

I'm sure you've already considered these alternatives but at risk of insulting you, I'll mention them anyway. Are you sprung in the rear as heavily as good hadling and balance will permit? Same goes for N2 in the canisters. I skimmed through the 2 aerodynamic sections in Milliken's Race Car Vehicle Dynamics this evening and didn't see any formulae that would help you with that dynamic. So many factors come into play that I don't know how one could quantify other than the pitch vs speed data that Motec could give you. After that, I guess it becomes give and take as do most aero problems.

Tom W

No offense taken. Spring rate is certainly a factor that has been and will continue to be evaluated with my car. Until I added the MoTeC data system we had no way to actually measure squat on acceleration (no pun intended) and it took me a while to get all set up so I believe the numbers I'm getting out. My current springs are 650/800 (f/r) and we may boost the rates even more. Spring rates are a trade-off and we had reduced then in the past (when we didn't have MoTeC data) to improve the car's handling. Other factors we will examine is changing the static rake so that the effective rake out on the track provides the right angle of attack for the front splitter to help get the front to where we want it.

Mahler9th

I'll bet that Porsche evaluated most/all of the racing variants of these parts, and I'd guess that the information isn't in the public domain. I remember years ago when it was said that Cups had an aero advantage over RSRs at Daytona... but that was long ago.

If one were friendly with the engineer for a pro team that has a relationship with Porsche and an appropriately robust amount of experience, one might pursue that connection (wink).

I do believe wind tunnel work can account for ride height changes (how hard can that be given the budgets and technical expertise involved).

In TW's case, I doubt there are any fractions of tenths to be gained trying to quantify aero with data. Sure, you can measure a lot of things with a lot of sensors, but achieving lap time benefits that amount to fractions of tenths, let alone tenths, would be challenging in my opinion. Perhaps a fun exercise... not unlike building a ship in a wine bottle. I do believe that lap time can be reduced with a thorough testing regimen with a variety of aero alternatives at hand. I have done a little of this with front splitter and dive plane alternatives on my car, and while not scientific, the results are evident in the seat of the pants.

One cool thing about these cars is that the folks that race professionally, like TRG the Lizards and so on work hard to sort out what works best, with the help of Porsche in many cases. This type of thing has been going on for many, many years. There is relatively little undiscovered territory on many of these topics. These folks are generally accessible, and can just tell you what will help, what is better, and what differences things make. Unfortunately, many amateur budgets preclude ideal implementation.

JackOlsen

This isn't exactly what you're looking for, ut if you're already set up with a data logger, you can do your own my-car-in-the-real-world testing. I strapped a pair of $5 (used, ebay) sensors from a 1995 Lincoln Continental to my front and rear suspension pieces, and did some steady-speed tests (both directions to correct for wind) on a remote stretch of freeway near my house. I was able to see consistent and repeatable changes in ride height from as-small-as-4-degree changes in my wing setting. I packed up all my pieces, and tested them all one Saturday afternoon.

It works on the track, too.

Accelerator

Leigh2.

This is the data I read some time back on the 6 Speed forum and its source. Data was compiled at speed equivalency of 125mph. Pretty flimsy DF, huh? You might also find some data in back issues of Porsche Engineering Magazine.



Sport Auto, they use the Daimler wind tunnel at Stuttgart University and are the only ones in the world other than Porsche to test lift and downforce and CDxA.

Your statement is right, net lift is close to zero for the GT3RS (and for the TT):
Front: - 19kgs
Rear: 25kgs
Net: 6kgs of downforce

996TT:
Front: - 7Kgs
Rear: 6kgs
Net: -1kgs lift

Accelerator

Leigh2.

This is the data I read some time back on the 6 Speed forum and its source. Data was compiled at speed equivalency of 125mph. Pretty flimsy DF, huh? You might also find some data in back issues of Porsche Engineering Magazine.



Sport Auto, they use the Daimler wind tunnel at Stuttgart University and are the only ones in the world other than Porsche to test lift and downforce and CDxA.

Your statement is right, net lift is close to zero for the GT3RS (and for the TT):
Front: - 19kgs
Rear: 25kgs
Net: 6kgs of downforce

996TT:
Front: - 7Kgs
Rear: 6kgs
Net: -1kgs lift

mark kibort

I can only say that I have tested the GT3 cup wing at 60mph to 120mph.

I have all the data for the different speeds, but it was something like 250lbs of downforce at a 7.5 degree wing setting.

I went from a stock raised and inclined stock wing, that generated 80lbs at 10 degrees.

the change gave some boarderline undriveable characteristics. (too much push) after adding a splitter
hood vent, adding more to the splitter, less wing inclination, the push went away.

mk

stownsen914

Jack,

What kind of sensors were these? Some kind of linear motion sensors?

Scott

JackOlsen

They're linear potentiometers, components for 'air ride' systems used by just about every auto manufacturer. They have a power wire, a ground wire, and a wire that puts out 0-5V, depending on position. (Disclosure: I'm a guy who can't get his head around electrical stuff at all, and I figured these out -- they're that simple.). The sensors are easy to find new for $95, but owners of cars with these systems are constantly converting back to traditional springs and shocks, since the more complex air ride components tend to fail as they age. So it's not hard to get the sensors cheap through a wrecking yard or ebay. (I'm told that Range Rover dealerships are another good place to find them, since their implementation of air ride is as complicated and unreliable as you might expect.)

Once you attach them to a fixed part of the chassis and a moving part of the suspension, you can create a math equation (I'm a simpleton in this department, too) to normalize the readings front and rear, in case the total travel is different, relative to ride height change. You can also use bags of sand or salt to establish real-world numbers for an idea of how many pounds of work your aero stuff is actually doing. Of course, it's relative -- with my pieces, I was able to do runs with no wing or splitter to see the enormous amount of lift my early 911 generated at speed. Those wind tunnel numbers for the modern GT3 and TT are phenomenal, compared to the original 911 body design.

When I did this testing, I first tried infrared distance sensors that were repurposed photocopier parts. Unfortunately, they didn't have the accuracy I needed. But if you start on page 2 of this thread, you can see a lot of the tests I did looking at front and rear ride height relative to various aero pieces on my old 72. The cantilever effect of too much rear wing was an interesting discovery, for me.

mark kibort

you should have seen my weight set on the wing, with a set up to spread the weight and not bust it in half! I think I ended up with about 200lbs on the wing before i started getting nervous. (to match the spring compression marks met while traveling 120mph)

Mk

chris walrod

How about 4500lbs?

High tech simulation