911addict

Toby, good to meet you and the guys.
Were both comparisons done at Brunters?
As you say its rather a rough surface (and is it really uphill?). My thinking is that the rough service may have caused more resistance (I don't mean traction, but actual pummelling) on our tyres therefore bringing speeds down.
Although cold, the air was very damp: we didn't seem to have traction issues at all, but maybe micro-slippage as well, occurred at such high speeds????
ps: did you notice how icy the roads got when the sun (what sun?) went done?

TB993tt

911addict and JBL930, I'm afraid I don't remember your names but DO know who are from your cars in your sigs -great to see you guys, what a pleasant way to spend a Saturday afternoon

Graeme -I would bet that the GT2 did come with the undertray for the road car, there would be no reason to leave it off seeing as it doesn't weigh very much and any smoothing of the airflow must be a good thing ?
Here is another data screen shot for you - what is amazing is how consistent the data is, virtually all runs end at 190mph and the acceleration is within 1sec frpm 40mph to 190mph !


rinlv1
The spoiler opening would probably relieve some drag wouldn't it ? although I am not sure the fibreglass spoiler has enough integrity to have a hole hacked into it.
Here is a pic of the splitter/spoiler combination I will try next:
Copyright JJayB

This spoiler is not my favourite looks wise and is supposed to be in conjunction with the GT2 bi plane however I think it will work OK with the ttS wing - I look forward to trying it on the airstrip in the new year - the difference over 170mph is so obvious (in the original chart I posted) that any difference will be easy to spot.

Compared to the run before it took 286 metres more to hit 190mph - that is proper drag
911Addict
The original run was done at Brunters also, exactly the same although temp and pressure were different..... As we discussed yesterday, the runway will not give the best acceleration numbers, firstly it is uphill most of the run and secondly that surface is pretty horrible. A smooth flat surface would be worth 3 or more seconds up to 190mph IMO.
My 60-130 times on this surface were arond 8 secs (100-200kph ~7s) which is 0.4/0.5s slower than on my usual smooth, flat "track"......
Here is a shot from the driftbox (before it packed up) note the slope !


Aceparts
I "tested" the new aero wipers and can confirm that they worked as 190mph approached and didn't go flying off into the scenery !

Stummel

Michael (mw911 on RL?) had a significant improvement with the OEM Porsche RS side flaps in the front, not the Techart ones.

His NB 993 tt is stable at 345kph (GPS) and can be driven one handed at 300kph.

Maybe he will chime in.

TB993tt

Did he have to go with non turbo 993 front to accomodate the flaps ?

Here are some pics of the various options, it is interesting to see the differences:
Firstly the RS side flaps, the sides look similar to the ttS sides and the front has a slightly more pronounced lip:


ttS lip with "custom" lower splitter

Next we have Techart (MOD500's car) which apparently is same stability/instability as stock:

Next Frankenstien's

This is what I have coming, seems similar frontal protrusion as RS flaps, presumably the side wing bits are supposed to provide directional stability ?

Stummel

He has a narrow body, so no turbo front anyway.

Jussi

Thanks from interesting comparision.
I also think that this "Frankenstein front spoiler" is not good for high speed because it surely increases air resistance (Cd). This can be seen from 160mph up..
Switching from 2WD to 4WD also "loses power" because
2WD's power is about 0.89 * power without loss and
4WD is about 0.83 * that. So that is 7% less.

Felix

Turbo front would fit NB as well.

JBL930

A couple of poor vids and pics on this page LINK Didn't get chance to ride in your car Phelix, maybe next time

Felix

After the two RS tuning cars mine's a bit boring!

mw911

I have a techart center frontspoiler (093.100.100.009), which was on the car when I bought it as a n/a car in 2001. This techart spoiler was combined to the original n/a corners. This was the same combination of parts that was used by RS on their 533 (?) PS car published in 4/1997. The press article is still on their website.

It is of note, that this spoiler has only two relative small openings.

In december 2004 we modified the car by putting the turbo motor and gear box in it with K16/24. Initially we noticed that with this front in combination with the OEM turbo heckspoiler (that was of course mandatory) the cars front felt very light at high speeds.
We first tried the techart front spoiler corners which made very little difference, however we then mounted the original RS front spoiler corners. The cars high speed stability improved dramatically. However, I had the feeling (at that time I did not had a drift box) that I lost ca. 10 km/h vmax.
Unfortunately I dont have a front photo because the car is at SHK now due to some major body work.

Michael

John H. in DC Area

This is an interesting discussion. Thanks for sharing your research, Toby. I am posting some relevant pics. Don't know who owns any of these cars...

Here is a race GT2 front spoiler which hasn't been discussed and looks purposeful, though obviously not as clean and simple as the Turbo S chin. I have a few pics of this spoiler on dark cars with a lighter meshing at the triangular corners, looks pretty good.



Here is a pic of the three spoilers in a row.



Here is a pic of the front spoiler Toby will be trying shortly, with the addition of a carbon fiber lip extending another inch or two. I have tons of pics showing many of these spoiler lips/side wings fitting very poorly, showing gaps at the connection to the underside of the stock Turbo spoiler. Hopefully the version he chooses will fit cleanly.






Functionality aside, I prefer the aesthetics of the Turbo S lip on Toby's car. That said, I'll never have the good fortune to contend with a 993TT in crosswinds at 190mph on the Autobahn or at Bruntingthorpe.

TB993tt

Jussi
This has made me really realise the effect of the aerodynamics at high speeds IMO The ~3 seconds and ~300m extra it took to get from 170 to 190 is all down to the new front spoiler causing drag, power wise it would have been about the same as with the 2WD since firstly I had full timing (I/C lead pluggedin this time) and it was 10 DegC colder with IATs of 21DegC max -you can see to 160 the performance is the same and it may have been even quicker now with the same aero as before.

Leon's Ruf did an amazing 198mph which I think on my car would be impossible without another 100hp ! Leon's had some great aero touches, with shaved gutters, Ruf front end and that smaller rear wing:


John H
Those pictures are great, the one with the three in a row is just georgeous and makes one realise instantly why we are so addicted to these cars
Those EVO front ends no doubt give the best stability and downforce but I bet you would struggle to get over 180mph however much hp you had

mw911
Thanks for sharing the information - I guess unless you datalog your acceleration like I "accidentally" did above it is hard to make a call on the exact difference (in high speed acceleration) that aero aids make - Is there any way you can log some of your high speed antics once your car is back up and running ?
Schmirler told me that the red 533hp car which did 221mph/355kph also was not planted at the very high speeds however it is all relative I guess since 221mph is a LOT more than 190mph !

Jean

A lot of great information TB, thanks for sharing it.

Also some great great pictures of 993TTs, I love that Arena red one at the front!

I just wanted to say that I have been looking in great detail at the datalogs, and it is very difficult to be able to make any conclusions, also there is a lot of calculus to be done to analyze from HP and torque curves..add to that the complexity of 4WD vs 2WD, different weight as well, and finally different front and rear spoilers!!

I cannot draw any conclusions, but two things I would like to mention as an opinion..

1) for the performance to drop as it did after about 160mph, the coefficient of drag (CD) needs to be seriously high, my calculations based on the datalogs put it at close to 0.5. TB's previous run (VMax, 2WD, 540HP) was right at around a CD of 0.34, which is close to the 993 GT2 drag coefficient. A 930 is only 0.36. The front bumper of the 997 with its large air intakes has apparently improved drag (and downforce) on the 997, so this is a bit of a contrast.

2) The datalogs (smoothened to 0.5s to reduce noise) are showing a strange behaviour in the engine HP curve, there is a hump right after shifting and then a sudden drop at around 235 into 248kph in 6th gear, and then the long Gs stabilize on a downward slope. This is not as a result of drag since it does the same in 5th. I might be able to show it in the graph below. The black line is the one I am writing about.



The only other explanation I can think of is downforce, however it is not a very logical explanation since the rear Turbo S wing is not high enough or with a strong angle of attack..

I might be wrong, but I cannot see drag doing this in this manner as a result of a front bumper and wheel well liners really.

Re. the rolling resistence:

Power to overcome rolling resistance = Weight (lbs.) x RR coefficient x mph / 375

The coefficient of drag for VERY smooth asphalt is 10 and for very rough asphalt is 22..

Poor asphalt: Power (BHP)= 3500 x 0.022 x 186mph/375= 38 Bhp
Good asphalt: Power= 3500 x 0.010 x 186/375= 17 Bhp

The difference in an extreme case is about 21BHP at 186mph sustained.

TB993tt

Jean
Many thanks for checking out the data....

Whilst you have the ability to crunch the proper maths regarding Cd, real hp being made etc I tend to try and look at all (reliable) test data which has been published.
In this instance I am referring to aerodynamic aids (or hinderances). The only sound data seems to come from the Sport Auto magazine tests where they actually put the cars in the wind tunnel and measure front and rear lift at 124mph -I have the data for many Porsches from these tests and also from the stuff written by Paul Frere which comes straight from the factory. there is also (surprisingly) some good tid bits coming from Porsche in Cristophorus and sometimes comments made to journalists (the reliable ones) when testing...

My "quest" for aerodynamic truth led to a little altercation with one of the chief Techart engineers recently at the Essen show. Techart were proudly displaying their 997 based GT Street which has been developed in the wind tunnel.

The bottom line was that when Sport Auto measured its drag its Cd went down to a pathetic 0.33 (from memory) from the 997tts 0.29 and it lifted ~9kg at the front with only 9kg downforce at the back (at 124mph) - so I put to him that basically they had taken a perfectly good slippery 997tt, dressed it in battle dress and cocked up its aerodynamics

The Techart eng was a bit taken aback by my analysis of (and knowledge of) the numbers and went on to say that the employees accompanying the car must not have "set it up" correctly, meaning the adjustable rear wing - naturally I goaded him that for the most important, most read test that the car will ever undertake (they were handing copies of the test out on the stand) they didn't set it up right ????? -you get the picture

Anyway the reason for the long rant is that if Techart can't get it right when they are acknowledged as one of the best Porsche tuners in terms of spoilers then what chance does Herr Frankenstien have when developed my front end in his virtual wind tunnel -he sells mainly parts for VWs, Audis etc.

Whilst my front end looks like the 997tt unit I would bet there is SOOOO much more going on with the 997tt stuff from the various angles of attack of all the leading edges to the way the air is ducted once it enters the spoiler, also the fact that my wheels stick out proud from the edges straight into the air stream -basically I think that those big inlet really blunt the front end and DO increase the Cd substantially.

Regarding the new found stability -Jean firstly mentioned the engine undertray, I think definately and in combination with the ttS rear spoiler and the 4WD (which has also altered the weight distibution slightly) these three things have made the difference -NOT the 997tt front end

Looking at Jean's long G chart below the drag seems to start slowing the car down at 200kph (124mph) relative to the other run -is this not how drag works, really increasing exponentially as the big numbers clock up ?

Of course their could be an engine problem, it just didn't feel like it -the 60-130s were all pretty much spot on (for Bruntingthorpe) and like you say with all the other variables: 2WD v 4WD, +50kg, lower ambient, higher pressure, I/C lead connected -it is a hard one to make an accurate judgement on....

Jean
Thanks for the explanation of the rolling resistance, with Bruntingthorpe there is additional resistance as the track, as well as being covered in repair bitumen sticking proudly out of the surface actually has some bloody pot holes in it and ruts and when you set off in 3rd and 4th and hit these irregularities, the car is almost "jumping" in the air and scrabbling for grip -thankfully there are no potholes at the faster end !

mw911

I will try it, when I have my car back (in februrary/march). Since 2 months I have a racelogic driftbox, I will report the data then.

Michael