I stuck these on in between my 2nd and 3rd session at roebling.

The car already has so much downforce that I was doubtful that I would be able to tell the diffrence on an unfamiliar small track, but I could feel the difference and was at least 0.5 Secs faster. No changes to the car and 2 sessions within 1 hours, same temps, same clouds. If anything it was a bit hotter.

Also faster on the long straight because my exit speed was that much higher.

 

is the gurney a motorsport part?

 

No just something my local shop said I should try.
they also made some nice brackets to put the bolt through on the front CUP lip.

No my rearview mirros is even more useless..

 

bolts for the front cup lip?

 

In the 10 there are 2 screws going up into the car, they keep it all together. on '07 you did not need the screws, but I think these flap in the wind without them.

 

ah yes the ones at either end right in front of the wheel well/lining

 

Yes, they also hold on some black little flap.

 

Putting a Gurney flap at the end edge of an airfoil changes the Kutta condition and thereby produces
more downforce. However because of the flow separation stream of such a trailing edge, the drag also increases if the angle of attack of the wing where the gurney flap is installed is higher than some degrees, and in car wings usually is.

Some modifications on the Gurney flap can reduce this flow instability, which would result even in a drag reduction compared to the drag prior to the gurney installation , such modifications are slits or cuts or halls on the Gurney (lots of motorsport teams do that Mitsubishi, Peugeot etc )or a Gurney that is not in a 90degrees angle with the wings surface.

I have installed one in a oem RS wing that has a smaller angle and completely different design (not mine) , I personally couldn’t feel the difference in downforce driving but neither saw any difference before and after by timing 100-200 klm/h runs so I guess at least my Gurney lip didn't added extra drag.

With that being said I can’t believe that you could get a half second advantage from it or from adding the front lip modification. Because I am a fun of the placebo effect, I think that you can attribute the lower times to you feeling more confident to push the car after the mods, which is a good thing nonetheless.

John

 

The explanation of the half second is plausible, at least to me. If the aero mod didn't inhibit the achievable top speed (which was probably very low compared to real limits of the car, say 130-140 mph) and it did result in a higher apex speed leading onto the longest high speed sections, a half second is there for the taking. This assumes a typical 1:50 to 2:10 lap time give or take and a driver working sensibly within limits. Conversely, if the real issue is a car and driver already on the edge using everything the car and driver have to offer, added downforce leading to higher apex speeds and higher track-out speeds, well, that might be shaving 100th's and discernible only through data acquisition ... in any case, these are just points plotted on a continuum.

 

You have to understand RR. The exit speed from a very fast turn 9 is key to a fast lap leading to 1 of the fastest straights in North America. Also turn 3 is very fast and downforce is key.

Peter

 

I can't follow your flow stability technical stuff, but I am sure you have a point and I will see at Sebring and other tracks to see what the differnce is. I might lose a few MPH at Sebring, but make up in T17??

I doubt the placebo effect, I did not expect to be able to tell any difference at my driving skill level.
I was on my limit in both sessions and I never thought about it, I was just running around having fun not really looking at laptimes, but it did feel like more grip.

Yes, more top end speed (150MPH) because much more exit speeds out of T9, about 110MPH.

Difference was easy to see on Traqmate data.
Much faster out of T9 and much faster into T1 from 150MPH -80MPH while turning in, setting up for T2, turn in at about 70 Mph and a little faster T3 going about 100MPH. Small track, not slow track.

 

I agree that an increase in the downforce if not cancelled by a big increase of drag would help lower lap times in especially a fast track with hi-speed turns.

What I doubt is that the increase of downforce with the addition of a gurney lip like yours or mine, together with a probable increase in drag are significant enough to cut down half a second in a 2 min lap.

To throw some actual numbers in from a 996 RS wing as measured in a wind tunnel by Manthey. The difference in downforce at 160klm/h between when the RS wing was set at almost parallel to the ground (normal position from factory) and when the RS wing was repositioned by using the 8degree shims was 32kg.

Only 32 kg gained from a huge difference in the angle of a wing that has an area surface of the RS wing..
With the 1.RS wing dimensions I took from my wing using an approach angle of 8 degrees and doing some rough calculations from a book I have in hand, I came up with 1.2 kg of added downforce for a Gurney flap of 1,2cm height at 160klm/h completely ignoring the increase of the drag co-efficient.

Hence I don’t believe that this added kilo on the back can ever cut down lap times by half a sec or can be measured clearly even by data acquisition machines unless a robot is driving steady on a track at identical lines..

John

Ps. I like the look of the gurney lips so that’s why I installed mine. : )

 

I have no idea how much down force the lip and flap make.

I agree the difference is big.
It's not even 2 minute lap:
Session 2 I did steady 12 laps, all 1:21's 1x 1:221 and 1x 1:208. Session after no changes at all besides adding the lip and flap and maybe 1/4 tank less gas. I drove hard, pushed like hell.

1 1/2 hour later, pushed like hell: 11 laps, all 4x 1:19 4x 1:20 and 1 1:21 (Traffic).

Same driving, not more confidence, either the car slides or it does not..

 

^ Peter I am not sure about my numbers above either but I just enjoy the discussion.

It’s not my area of expertise, I bought some books recently for another project I am doing and tried to explain the Gurney lip's function better firstly to me.
The about 1kg number I come up with is based on rough percentage increases of downforce from a tabled analysis in one of my books, I just altered the wings dimensions based on the RS wing and set a 2% of airfoil chord in height (1,2cm) and recalculated the equation.

When I bought mine my primary target was to reduce drag with it because I had installed the 8degree shims on the RS wing and I could feel and measure with timed (100-200klm/h) runs an increase in drag at high speeds with them on vs without.
My decision was based on some articles I have read back then, that suggested that depending on the angles of attack the gurney lip not only increased downforce but also reduced drag besides it was cheap and looked good.

My target was not met I didn’t see any difference in reduction of drag with it and fortunately neither an increase. Since it looked better I decided to leave it on and putted back the 4 degree shims which don’t affect car times almost at all or at least they aren’t apparent until 200klm.

So leave it on and try it more, maybe I am completely wrong and it really adds more downforce besides as I said it surely looks good.

Cheers

John

 

Just post an email to Norbert Singer and see what he advises.