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-   -   Q&A Porsche discussion (http://www.motorworld.net/forum/showthread.php?t=11873)

st-anger 06-22-2004 03:43 AM

Q&A Porsche discussion
 
...the name says it all, here you can post all your questions about Porsche in general as well as all the other things of interest in automotive industry and engineering...
as you know i´m kinda busy so plz be patient when i can´t answer everything immediately, but i´m sure that there are lot´s of ppl out there in JW land who know quite something, and everyone´s invited to contribute to the discussion... :P

st-anger 06-22-2004 09:45 AM

MOVED:

posted by Kangaroo Boy

Just Curious,What Porsche Models had the Pushrod Air Cool Flat 4 engine?Are they the same engine as the Vw Beetle?

answer by Schwalbe JG 44

For answer your question Kangaroo Boy, the 356 series of Porsche have the same engine than VW Beetle.

The displacement has evolved during the years at the level of the series 356

1948 Porsche 356/1: Air Cooled Flat 4, 1131 cc / 69 cubic inches, 35 hp @ 4000 rpm, Top speed 135 km/h / 84 mph.

1955 Porsche 356 Speedster: Air Cooled Flat 4, 1488 cc / 91 cubic inches, 55 hp @ 4400 rpm, Top speed 160 km/h / 99 mph.

1960 Porsche 356 B Roadster: Air Cooled Flat 4, 1582 cc / 97 cubic inches, 90 hp, Top speed 190 km/h.

st-anger 06-22-2004 09:49 AM

MOVED:

posted by Porsche_Cayenne

Uhm , I was thinking about the differences bitween Cayenne S and Cayenne V6 3.2... later all the engine differences, is the write on the back of the Cayenne V6 black as Carrera 2, or silver as Carrera 4?
I know Cayenne S has got silver write... but Cayenne V6?
I think that black write as "carrera" is horrible, in fact I'd go for the silver write "911" if I have a Carrera 2


:arrow: ...all Cayenne V6 models have that black "Cayenne" badge...
only "S" and "TT" have a silver one...

st-anger 06-22-2004 09:51 AM

MOVED:

posted by Apac102

I just watched the CGT video and Jerm was complaining about that the car is nimble and you always gotta be on your toes. When you drove it, did you find the same problem? Was it really that much...especially when the Stig went around the bend and he spun out a couple of times.

:arrow: ...first, the CGT is no VW Golf, it´s more or less a race car for the road, i think it´s clear that JC is more the Benz guy
you know i used to drive Porsche since i got my driving licence, so i´m quite used to the typical Porsche handling and manners, especially since i´m working for Porsche it´s also my job and daily life to push the Porsche cars to the limit, also on the race track...
so i had no problems with the handling of the CGT, i expected it to feel like it felt, only "problem" was the clutch, but it´s really not that bad, again the press cars for all the tests are pre-production cars, with the final production version one can drive off even without adding too much gas, just like in a std. Porsche...
to drive the CGT at the limit is quite a challenge, that´s for sure, so not a really surprise for me that the Stig spun it, although he seems to be a very skilled driver, but that´s not that bad, only when pushing too far you´ll discover the limit of the car so that´s not a problem neither of the car nor of the driver....


Why Carrera GT has such a knife-edge on limit handling? because of the sophiciated aero dynamic or suspension design/set-up with CGT? or just simply because this car is too quick for "average driver"(sounds like "normal driving condition" on PCCB to me)

answer by ChrisAW11

It all lies in the basics of quickness and grip.
Here you have a possible acceleration/slip angle diagram of a slow car:
http://www2.freepichosting.com/Images/421514187/1.jpg

This again is a possible acceleration/slip angle diagram of a fast car:
http://www2.freepichosting.com/Images/421514187/0.jpg

Now slip angle is related with the steering wheel position of the car - actually it means the amount of "sideways" that the tires are going.
The possible acceleration that the car can deliver is the grip that you have left.
Obviously, the grip curve of the racecar goes up very fast, which means that whenever you start turning the steering wheel, it will be able to follow and turn like a madman. The slower car needs more slip to do that, and even at it's optimum slip angle, it just hasn't got the same sort of grip that the racecar delivers, which means it can't take the corner as quickly as the grippier car.

But then, you'll notice that after optimum grip, the racecar very quickly loses all the grip, while the slow one still has a good amount - that means, when you ask too much from a racing car, there is just about nothing left to save you, and you'll spin out. In the slow car, you'll have a good percentage of grip left, and in most cases you'll make it back into the safe side of the acceleration peak without leaving the road.

A grippy tire slips less, that's the basic principle to remember. It is directly related to another principle, "the higher the limits, the less fault tolerancy".

The Carrera GT obviously has enormous amounts of grip, very high limits, and thus it just hasn't got the fault tolerancy of a slower car.

st-anger 06-22-2004 09:56 AM

MOVED

posted by jon_s:

Mr St-Anger, I was woundering if you could cast any light on a slightly sore point as far as the UK press is concerned.

It concerns the life of the ceramic brakes, which are supposed to have a service life of 186,000 miles ( -is that right!) but are lasting significantly less than that (In some limited cases) Cost of replacement is a whopping £27,000 (Enzo brake territory!).

Porsche are apparently claiming that track days are the problem! What exactly did Porsche expect their owners to do!

I sure hope there is a fix in the pipeline, as £27,000 to replce them is quite frankly taking the piss.


:arrow: … a good statement in that context: PCCB´s are a political hot potato within PAG”
now that´s a fact, that there´re some problems, or better, had been some problems…
to quickly answer your first question: yes, under “normal” driving conditions PCCB´s do have a service life of up to 300.000 km ( ~186.000mls )…
when they´re used on the track they sometimes have to be replaced after 10- to 15.000km ( ~8000mls )…
there´s been a huge discussion, some dealers changed the rotors under warranty, some not, especially in the USA....don´t ask me why???
so PAG added this disclaimer:

circuit racing or similar extreme driving conditions can significantly reduce the overall life expectancy of even the most durable pads and discs. It is therefore important – as with conventional steel high-performance brakes – to have all PCCB components properly checked and replaced, if necessary, after every track event.

therefore, anyone using the PCCB brakes on the track must be prepared to replace all components after each track event. cast iron rotors are cheap consumables but ceramic composite rotors are most certainly not! ergo, a track car is exactly the sort of car which should not have PCCB brakes. there are good reasons why you will not find these brakes on any of Porsche’s race cars…
there are three main problem areas with ceramic composite brakes:
first, the rotors overheat and fail.
second, the ABS system has not been modified for the PCCB rotors which causes less than optimal ABS performance and also damages the rotors. third, the pads are not able to handle the heat and are quickly destroyed once overheated. the lower unsprung weight that these brakes offer is noticeable as is the total lack of fade. and I do believe that ceramic-composite brakes offer tremendous potential, but Porsche introduced them too soon and they are just not ready for consumer use.

just read this:
DC introduced a ceramic brake pretty similar to the PCCB on a special limited production CL 55 AMG, called “F1 Edition” model. By that time, Mercedes had high hopes and big plans for introducing the ceramic compound brake on other models too, but they didn't.
and here's the question: why didn't they do it?
remember: we're talking about a multi-billion dollars super car manufacturer with billions of dollars of production/research budgets...

so, one major issue regarding PCCB development was cost, so they tried to adapt the current brake system with all components to the PCCB. same applies to tires.
a perfect and optimized PCCB system would require different components (incl. completely different electronics and mechanial parts) and of course optimized tires, not to speak about the pads which could be better but also much more expensive and no one would pay 1000 bucks for one set of pads which last 2500 mls.

PCCB works pretty well on the street, even if it needs some temperature to achieve best results. as far as replacement/maintenance cost is concerned, I think we can't blame a manufacturer if a brake isn't "track worthy", actually which brake is "track worthy"? even the beloved 380 mm steel discs need replacement after some tough track runs, so right now, the PCCB is at the beginning of development, it is a pretty new product and for the street at least as good as the steel brake, why??? PCCB does NOT provide a shorter braking distance because of the facts mentioned above.

so, PCCB is still in it's first generation but the new GT2 (MY 2004) already has an overworked PCCB system (incl. some of the hardware components and some aerodynamical changes to supply the brake swith more air) and it remains to see how good it performs on the track, so again: if you're into serious track racing, going for the regular steel brakes might be a better idea.

btw, the PCCB brake system on the Carrera GT is completely different to that of the 996 Models with the PCCB system installed:
the diameter of the disc is greater than that of the smaller system on the 996 models. (380mm vs 350mm), thereby increasing its efficiency. the cooling system of the brakes is much more advanced and channels significantly more cooling air to the brakes than on the 996 models and it has specially developed brake pads.

http://img63.photobucket.com/albums/...anger/VR-1.jpg
http://img63.photobucket.com/albums/...anger/VR-2.jpg
http://img63.photobucket.com/albums/...anger/VL-2.jpg
http://img63.photobucket.com/albums/...anger/VL-1.jpg
http://img63.photobucket.com/albums/...anger/HR-1.jpg
http://img63.photobucket.com/albums/...anger/HL-1.jpg

yg60m 06-22-2004 10:07 AM

It is hard to explain : i read several articles where it is written that the sound of the last 997 is the result of extensive work on exhaust, engine ... That leads to a personal reflection : When i hear the sound of a 996 on tv and even the CGT (only on TV) they doesn't sound very "natural", more synthesizes and even if it is awesome (the CGT is incredible) this "synthesize sound" is ... weird, as if computer-arranged.

It's not easy to explain, it's the difference between the air-cooled 993 and the water-cooled 996 which try to seems like air-cooled :?

My question is : how does it sound in real ?? (CGT and 997)

lakatu 06-22-2004 11:33 AM

Thanks st-anger for the new section. I really like the idea.

I have been trying to comprehend the impressiveness of the CGT lap time (7.28 8)) and the decline in lap times for 911s in general over the years on the NS. I started out thinking why is it so hard to make improvements to lap times. To answer my question I started thinking about the physics that are required to improve the performance to lower the lap times. I have a few ideas but in some instances they don’t seem to make as much sense as in other instances. I was wondering what other Porsche fanatics thought about these ideas and what everyone’s thoughts are as to what has been the single biggest contributor to lower these times i.e. power/ weight, improved braking, suspension refinement or tires. I think to some degree the answer is improved power/weight but that is just my opinion. However, I think the answer is much larger than that as I hope is obvious from my examples.

Here is what I have come up with. When you look at lap times and performance increases there obviously isn’t a linear relationship. For example, an increase of power/weight ratio that is 2x doesn’t result in a lap time that is ½ the original. After looking back through some old physics books I notice that circular motion, and acceleration formulas are all directly proportional to the square of velocity. My assumption is that during a lap of NS the driver is constantly accelerating, braking or cornering and that to improve the lap times the forces required to improve the times would have to increase as the square of the change in velocity.

Let me use an example. In a prior post I have shared that I have seen a posting of a 1987 911 by Auto Bild with a lap time of 9:22. I calculate this is an average speed of 132.5 km/hr. Porsche drivers in the MKII 996 posted a time of 8:20 which is 150.0 km/hr or a 13.2% increase. Based on my simplified assumptions, I figure to increase average lap speed by this amount would require 1.132^2 or a 28% increase in the forces of acceleration, braking and turning. That seems to check out because I calculate that the power/weight has improved 24% and the lateral acceleration 13% and I’m not sure about the braking. Obviously all these forces would not have to increase in the same proportion acceleration could increase more say that braking or lateral acceleration.

However, when I use an other example the GT3 RS vs the CGT I get average speeds of 160.6 km/hr and 167.4 km/hr respectively or a 4.2% improvement. I calculate this would require a 8.7% improvement in accelerative force. That doesn’t seem right because the power to weight ratio of the GT3 RS is 3.6 kg/hp while the CGT is 2.4 kg/hp or a 33% decrease. Based on this I would have expected to see a larger improvement in the CGT’s time relative to the time of the GT3 RS.

So maybe there is a breakdown in my assumptions that the driver is always in a state of changing the speed of the car or in other words is always accelerating. If this were the case and at times the NS driver maintains a constant velocity the physics laws governing acceleration wouldn’t apply and other factors maybe working to change lap times.

For example, while I haven’t seen the NS I have heard reports that the surface conditions are challenging and I figure that a suspensions ability to remain controllable while absorbing bumps and imperfections maybe a limiting factor. What I mean is that a driver may not be able to continue to accelerate because the cars suspension is not able to maintain stability at faster speeds and the car would be in a state of constant velocity. Therefore, some of the improvements in average lap speeds may not be due to an increase in the generating forces but the refinement of the suspension to deal with road irregularities allowing faster speed through those sections.

I might be alone here, but I find this discussion interesting and any feedback would be helpful. I figure it is possible that I am completely wrong in my application of physics or there maybe other factor occurring that I haven’t even thought about. Any thoughts?

Edit: An earlier post had power to weight ratios taken from various magazines. Later I noticed that these were different from the figures reported in Sport Auto and Auto Bild. The updated information shows a 33% decrease verses the 50% quoted earlier.

lakatu 06-23-2004 12:56 PM

Thanks st-anger for the 997 material. Reading the Autocar article I had a question and a thought. Since Porsche has realized that their cars are faster on NS with Pirelli tires why wouldn't they work with Pirelli to create special tires for the 997? I have heard that Michelin spends more R&D than other tire makers is that part of it. BTW wasn't the old Pirelli P7 a specially designed tire for the 930?

The other comment I had is I have noticed a reoccurring theme as the 911 has changed over the years. This is especially true from the 996 on...which is that the more refined and controlled Porsche makes the driving experience the less desirable and fun their cars become especially for the purist or skilled driver. Any thoughts on this. A similar comment was made in the article in GT Purely Porsche article that reviewed the GT3 RS compared to the Carrera RS. http://www.motorworld.net/forum/show...=asc&start=180

st-anger 06-23-2004 01:41 PM

Quote:

Originally Posted by lakatu
Thanks st-anger for the new section. I really like the idea.

I have been trying to comprehend the impressiveness of the CGT lap time (7.28 8)) and the decline in lap times for 911s in general over the years on the NS. I started out thinking why is it so hard to make improvements to lap times. To answer my question I started thinking about the physics that are required to improve the performance to lower the lap times. I have a few ideas but in some instances they don’t seem to make as much sense as in other instances. I was wondering what other Porsche fanatics thought about these ideas and what everyone’s thoughts are as to what has been the single biggest contributor to lower these times i.e. power/ weight, improved braking, suspension refinement or tires. I think to some degree the answer is improved power/weight but that is just my opinion. However, I think the answer is much larger than that as I hope is obvious from my examples.

Here is what I have come up with. When you look at lap times and performance increases there obviously isn’t a linear relationship. For example, an increase of power/weight ratio that is 2x doesn’t result in a lap time that is ½ the original. After looking back through some old physics books I notice that circular motion, and acceleration formulas are all directly proportional to the square of velocity. My assumption is that during a lap of NS the driver is constantly accelerating, braking or cornering and that to improve the lap times the forces required to improve the times would have to increase as the square of the change in velocity.

Let me use an example. In a prior post I have shared that I have seen a posting of a 1987 911 by Auto Bild with a lap time of 9:22. I calculate this is an average speed of 132.5 km/hr. Porsche drivers in the MKII 996 posted a time of 8:20 which is 150.0 km/hr or a 13.2% increase. Based on my simplified assumptions, I figure to increase average lap speed by this amount would require 1.132^2 or a 28% increase in the forces of acceleration, braking and turning. That seems to check out because I calculate that the power/weight has improved 24% and the lateral acceleration 13% and I’m not sure about the braking. Obviously all these forces would not have to increase in the same proportion acceleration could increase more say that braking or lateral acceleration.

However, when I use an other example the GT3 RS vs the CGT I get average speeds of 160.6 km/hr and 167.4 km/hr respectively or a 4.2% improvement. I calculate this would require a 8.7% improvement in accelerative force. That doesn’t seem right because the power to weight ratio of the GT3 RS is 4.65 kg/hp while the CGT is 2.29 kg/hp or a 50% decrease. Based on this I would have expected to see a larger improvement in the CGT’s time relative to the time of the GT3 RS.

So maybe there is a breakdown in my assumptions that the driver is always in a state of changing the speed of the car or in other words is always accelerating. If this were the case and at times the NS driver maintains a constant velocity the physics laws governing acceleration wouldn’t apply and other factors maybe working to change lap times.

For example, while I haven’t seen the NS I have heard reports that the surface conditions are challenging and I figure that a suspensions ability to remain controllable while absorbing bumps and imperfections maybe a limiting factor. What I mean is that a driver may not be able to continue to accelerate because the cars suspension is not able to maintain stability at faster speeds and the car would be in a state of constant velocity. Therefore, some of the improvements in average lap speeds may not be due to an increase in the generating forces but the refinement of the suspension to deal with road irregularities allowing faster speed through those sections.

I might be alone here, but I find this discussion interesting and any feedback would be helpful. I figure it is possible that I am completely wrong in my application of physics or there maybe other factor occurring that I haven’t even thought about. Any thoughts?

…well, really some nice thoughts, i´m especially glad that you´re dealing with all this already quite professional, i´ve gone through your calculations a bit, also through your thoughts and you are basically on the right way… i´d say on the chassis/suspension side there´s quite some scope left, definitely on the factory cars, on the other hand the tuners are quite near the limit, there´re special NS suspensions mainly from “Bilstein” undriveable anywhere else but bloody effective on NS but a good setup for NS is nearly an impossible task, quite some compromises have to be made, again we can´t compare NS with a regular race track like HHR…
so suspension is not the limit on NS these days, sure it´s at the limit, but EVERY single part is at it´s absolute limit on a fast lap on NS, IMO the main influencing factor are still the tryes…
so acceleration, grip lateral g´s are mainly limited because of the tyres, we tested that excessively with more or less three manufacturers for our Porsche models, Michelin, Pirelli and Conti, nowadays Michelin and Pirelli only, but now we could start an endless discussion, as you know Pirellis were significantly faster on NS but again we can´t equip a car with the tyre XY only because it´s 20sec faster on NS, it should be driveable, especially in the wet which is a key point for our sports cars, they should be driveable every day, for shopping, in the city, but also on the track, so it´s always a huge compromise.
again we have to talk about the tyres when we´re talking about increasing forces, for the suspension/chassis forces up to 2+ g´s are no problem, but the tyres have to deliver this performance as well, on all the different surfaces… and that´s the point again, sure with racing slicks we can drive whatever g´s but this is not the task of a Porsche or sportscar in general, as i said some time before only very very few ppl will ever explore the potential of their e.g. CGT or GT3RS, even i have to try hard after driving Porsches for ~ 20 years now…
personally i only know 2 guys who can really push any Porsche to its limit: WR and Roland Kussmaul…
in the end it´s a bit hard to characterize NS on theoretical physics, as well as CGT and GT3RS, they seem to be on quite the same performance level but the RS is not even close to the CGT…

lakatu 06-24-2004 03:09 PM

Thanks st-anger for the information. So it sound like the limiting factor that prevents the CGT from utilizing the 33% lower power/weight ratio over the GT3 RS to post an even lower time is the grip available from the tires. You can’t be faster than your weakest link :wink: . Makes sense since all of the acceleration/deceleration and lateral forces have to be transmitted through the tires.

It looks to me like the decrease in power/weight ratios over the years is the main factor decreasing NS times for the 911 from 9.22 (1987 911) to today’s 8.20. Do you agree and how much of a difference do you think the suspension improvements over the years make?

Porsche, for some reason not clear to me, has always tended to have smaller wheels than would fit under the car :? . For example, the 911 Club Sport which was aimed at track day enthusiast had 6” front and 7” back. While you could order a 7”/8” sport package on the base 911. Current 996 runs 8”/10” and I’m sure that these wider wheels along with improvement in tire technology has contributed to the big improvements in lateral acceleration.

I have wondered how much faster on the NS an older 911 with new technology tires and wider tire/rims would be :D . This is especially true for the 930 series that can handle 9”/12” verses the OEM 7”/9”.

There must be some reason for the smaller tire preference by Porsche. There are a few trade offs that I am aware of like potentially higher unsprung weight, increased rolling resistance and higher drag coefficients. But since the trend has been to wider wheels and tires over the years I wonder why Porsche didn’t do it earlier. Maybe there wasn’t enough money to develop wider Fuchs back then.

Any thoughts or comments on these issues :?:

ahmedgiyab 06-24-2004 03:39 PM

Hi! I have a question about the 911 series....

I heard that they are very reliable cars....I'm thinking of getting one (used model

1999-2000)....but since I live in Dubai, I'm afraid that the hot summers will kill the

car's engine....(note: most of the ppl who own a 911 here, they use them as a

secondary hobby car...but I would use it for everyday use.... :oops: )

I have a Merc and I didn't have any problems with it....so I didn't need to spend on

spare parts....I guess a 911's spare part cost more than a CL500... :shock:

Does it worth it for me to buy one....if yes which is the best buy (C2, C4, Conv....)?!

p.s. exclude the GTs and the Turbo.... :D

Thanx in Advance! :)

lakatu 06-24-2004 04:22 PM

Porsche has a reputation for testing cars in extreme climates in preproduction. Additionally, they have a lot of experience with racing in desert environments. Based on this, I don’t think that you should have a problem with the 911 in extreme hot weather. This is especially true, I would imagine, for the water cooled models you indicated you where interested in.

As far as which variation i.e. C2, C4, convertible. That is a personal preference issue. People who typically select the C4 do so because of the safety and traction advantages especially required in climates that have rain or snow. From what I know of Dubai that probably isn’t as much of a concern for your situation.

You still may enjoy a C4 for the added stability the 4 wheel drive gives at the limit. The C4 costs a little more and has more mechanical parts requiring potential repair and maintenance issues. Additionally, some indicate that there is more understeer associated with the C4 vs C2 and as a result prefer the sharper handling and lighter weight of the C2.

As far as a convertible, the soft top has les structural rigidity which affects handling somewhat and could result in squeaks and rattles as the car ages. Although Porsches are better than most in this regard. So if you like convertibles I wouldn’t be afraid to get a Porsche Cabriolet.

Overall if your interested in a sports car you can hardly go wrong with a 911 :D .

ahmedgiyab 06-24-2004 04:37 PM

I like the Carrera 4...(and the 4S...but its too expensive for me :) )....also what is very

attractive about the 911 that if you sell it later....you will get good money for it.... :wink:

Thanx for the info!!! :)

One more thing: Is the Boxter S is good as the 911?!

lakatu 06-24-2004 05:31 PM

Your right one of the attractive aspects of owning a 911 is the high resale value. As with any economic principle the price is determined by supply and demand. The 911 has always been in high demand and enjoyed a mystic partly because of Porsche basing so many extremely successful racing cars on the basic 911. Other factors that have affected demand include the appealing and timeless shape, performance, unique rear engine layout and air cooling along with the reputation of reliability and skill required to drive a 911 fast. It was kind of a badge of honor to drive a 911 because real car enthusiast knew it required skill to drive fast.

I personally think the historically high resale value may be somewhat different in the future. The reason why I feel that is due to the shorter life cycles of the various 911 model. For example, a 1978 911 SC looks almost identical to a 11 year older 1989 Carrera. At the time this kept demand high for the older 911s because well if it was clean people couldn’t tell it was an older car. Additionally, the newer car has lost some of the quirkiness that was part of the 911 charm and mystic. For sure the new 911 is a much better car and I think that they will always be in high demand and therefore have high resale values. I just think they may not be as high as in the past.

As for the Boxster S. It is a great car. The midengine design provides for a broader range of neutral handling. It isn’t quite as fast as the 911 due to the smaller engine and it is a smaller car overall. But basically they are similar especially their interiors. I don’t think they will have quite as high resale value as the 911. But they are cheaper and still a great car. I would look into the price of maintenance and repair for the Boxster verses the 911 if money is an issue. I could be wrong about this but I think that the engine may have to be removed to do tune-ups. Although the same may go for the 996. It might be something to look into.

Personally, I’m not a fan of convertibles so the Boxster hasn’t been a car that I have learned about as much as the 911. If you are interested in a Boxster I’m sure there are others at JW that could provide you with some additional information.

ahmedgiyab 06-24-2004 05:38 PM

I heard that most of the Boxter's spare parts are the same as in the 911. Yeah you're

right, the Boxster's price is 'falling ' faster than a 911. I like the 911 more....but a new

Boxster S costs the same as a 2001 911 C2....at least here in Dubai.... :)

I will see...it will be a "hard" issue... :)


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