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A concession to US emissions standards...

 
Old 11-10-2010, 04:37 PM
  #31  
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Originally Posted by ADias View Post
Have you driven a 2010 Golf TDI? I think not.
Nope, I usually rent something different when I travel to Europe. But given the choice, I always pick a gas car over a diesel. I like revs.
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Old 11-10-2010, 04:59 PM
  #32  
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Originally Posted by zanwar View Post
Diesel returns better MPG than petrol because the fuel contains more energy. The reason so many European cars burn diesel is because of taxation. Diesel fuel is taxed at a somewhat lower rate than petrol based on its energy content, so it's cheaper to run a diesel car over there. Diesels aren't particularly nice to drive either. There's a surge of torque but the engine is out of revs very quickly. It's OK in something like a Range Rover but it's no fun in a performance car.
1. I drove a VW Passat TDI regularly when I lived in Germany and cruised at 125+mph..... getting 30mpg while doing it. Otherwise, I got about 50mpg on the "B" roads.

2. Diesels are also more efficient because they have higher compression ratios...a fundamental thermodynamic efficiency advantage.

3. Diesels dominate at the endurance race.....Le Mans... Audi and Peugeot Diesels have been the top performers for some time.
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Old 11-10-2010, 05:04 PM
  #33  
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I wonder how the stop / start will work with a manual transmission? My Friends Panamera has it and I noticed it when driving, but it wasn't a bother.
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Old 11-10-2010, 05:09 PM
  #34  
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Originally Posted by zanwar View Post
Diesel returns better MPG than petrol because the fuel contains more energy. The reason so many European cars burn diesel is because of taxation. Diesel fuel is taxed at a somewhat lower rate than petrol based on its energy content, so it's cheaper to run a diesel car over there. Diesels aren't particularly nice to drive either. There's a surge of torque but the engine is out of revs very quickly. It's OK in something like a Range Rover but it's no fun in a performance car.
It's not just a cheaper fuel, the consumption of a Diesel engine is significantly less than a comparable gas engine.

Every single time I travel to EU (a few times a year) I rent a diesel, and they are absolutely GREAT, not sports car feel, but as a regular commuter or a sedan they are fantastic! The lower rev limit takes some getting used to, but it's perfectly fine for 90% of commuting we do everyday.

As to Tony's comment on Golf TDI. I rented even a smaller Golf TDI engine 1.6 (than what's offered here) last time in Germany, and I drove to Nurburgring for my track day and back (300 Km each way), it was GREAT. I did 220 KM/h on the Autobahn, went back and forth to work everyday for a week, and only had to fill-up 2/3 of the tank before returning it.
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Old 11-10-2010, 05:22 PM
  #35  
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Originally Posted by Macster View Post

Depends upon how the starter is constructed. In some cases the starter is an electric motor that is part of the flywheel and there is no starter gear to engage. The starter motor has enough power to spin the engine and start the car moving along and then then engine reaches sufficient rpms that it is started and E-Gas and the engine controller see that the take off is as about as seamless as it can be.

The starter may actually be a starter and alternator in one.
Reads like a description of Integrated Motor Assist, Honda's hybrid technology.

If they built in this kind of system with a decent electric motor, it could be used to allow a manual transmission car to run smoothly down to 0 RPM without having to use the clutch. Under about 900 RPM the fuel injection would stop and the electric motor would spin the engine, above that it would fire up and run on gas as normal.
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Old 11-10-2010, 05:24 PM
  #36  
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Originally Posted by zanwar View Post
Diesel returns better MPG than petrol because the fuel contains more energy. The reason so many European cars burn diesel is because of taxation. Diesel fuel is taxed at a somewhat lower rate than petrol based on its energy content, so it's cheaper to run a diesel car over there. Diesels aren't particularly nice to drive either. There's a surge of torque but the engine is out of revs very quickly. It's OK in something like a Range Rover but it's no fun in a performance car.
Not significantly more energy. Regular and premium grades of gasolines have a specific calorific value of between 42.7 to 43.5 MJ/kg while diesel fuel has a specific calorific value of 42.5 MJ/kg.

Gasoline density is 0.715 to 0.780 kg/l while diesel fuel is a bit densor at 0.815 to 0.855 kg/l.

Diesel engines deliver better fuel economy for mainly two reasons:

1) Diesel engines run unthrottled at the air intake. The benefit is pumping losses -- the drag of the engine having to "pull" air past a very restrictive throttle plate -- are much less for diesel engines vs. gasolines engines.

This is one reason why some gasoline engines are using intake valve lift and timing to act as an air throttle to lower pumping losses under some operating conditions. (Remember the majority of personal passenger vehicles operating at 30% of load or less most of the time.)

2) Diesel engines run with a surplus of air. In big rigs at idle the air:fuel ratio can be nearly 100:1. In passenger vehicles, the air:fuel ratio is much lower, my info is around 30:1, tops. IOWs, diesel engines are lean burn engines in that there is an excess of air in the combustion chamber at all times. Some gasoline engines are also now lean burn.

The theoretical air:fuel requirement for gasoline is 14.7:1 to 14.8:1 while for diesel fuel it is 14.5:1 so theoretically a diesel engine requires a richer mixture than a gasoline engine.

BTW, I owned a 2002 VW Golf TDi -- 1.9l 90hp and 160ftlbs variable vane turbo-charged diesel engine.

By way of contrast my 02 Boxster with its 2.7l engine delivered nearly 220hp but just 192ftlbs of torque.

The TDi was no rocket but it was no sled either. The car managed to keep up with traffic just fine and could run 100mph all day long even at high altitudes with no complaint.

Over the 120K miles I drove the thing it delivered on average just over 40mpgs under a wide variety of driving conditions, from short hops to multi-thousand mile road trips covering sometimes nearly 1000 miles per day of driving.

Sincerely,

Macster.
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Old 11-10-2010, 05:27 PM
  #37  
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Originally Posted by zanwar View Post
Reads like a description of Integrated Motor Assist, Honda's hybrid technology.

If they built in this kind of system with a decent electric motor, it could be used to allow a manual transmission car to run smoothly down to 0 RPM without having to use the clutch. Under about 900 RPM the fuel injection would stop and the electric motor would spin the engine, above that it would fire up and run on gas as normal.

But look at the added complexity... does that make sense in a sports car? Heck, I don't even need electric windows. Soon (if Eric Schmidt has his will) cars will drive us...

Last edited by ADias; 11-10-2010 at 05:46 PM.
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Old 11-10-2010, 05:52 PM
  #38  
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Originally Posted by ADias View Post
But look at the added complexity... does that make sense in a sports car/ Heck, I don't even need electric windows. Soon (if Eric Schmidt has his will) cars will drive us...
Sure there's added complexity, but you'd be removing complexity at the same time because you'd be combining several components into one. Also you wouldn't need a complex transmission like PDK, just a straightforward manual 6 speed with a clutch pedal. A motor that can smoothly spin up from 0 RPM to 7000 RPM has a certain sense of elegance about it.
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Old 11-10-2010, 06:01 PM
  #39  
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Originally Posted by Macster View Post
Not significantly more energy. Regular and premium grades of gasolines have a specific calorific value of between 42.7 to 43.5 MJ/kg while diesel fuel has a specific calorific value of 42.5 MJ/kg.

Gasoline density is 0.715 to 0.780 kg/l while diesel fuel is a bit densor at 0.815 to 0.855 kg/l.

Diesel engines deliver better fuel economy for mainly two reasons:

1) Diesel engines run unthrottled at the air intake. The benefit is pumping losses -- the drag of the engine having to "pull" air past a very restrictive throttle plate -- are much less for diesel engines vs. gasolines engines.

This is one reason why some gasoline engines are using intake valve lift and timing to act as an air throttle to lower pumping losses under some operating conditions. (Remember the majority of personal passenger vehicles operating at 30% of load or less most of the time.)

2) Diesel engines run with a surplus of air. In big rigs at idle the air:fuel ratio can be nearly 100:1. In passenger vehicles, the air:fuel ratio is much lower, my info is around 30:1, tops. IOWs, diesel engines are lean burn engines in that there is an excess of air in the combustion chamber at all times. Some gasoline engines are also now lean burn.

The theoretical air:fuel requirement for gasoline is 14.7:1 to 14.8:1 while for diesel fuel it is 14.5:1 so theoretically a diesel engine requires a richer mixture than a gasoline engine.

BTW, I owned a 2002 VW Golf TDi -- 1.9l 90hp and 160ftlbs variable vane turbo-charged diesel engine.

By way of contrast my 02 Boxster with its 2.7l engine delivered nearly 220hp but just 192ftlbs of torque.

The TDi was no rocket but it was no sled either. The car managed to keep up with traffic just fine and could run 100mph all day long even at high altitudes with no complaint.

Over the 120K miles I drove the thing it delivered on average just over 40mpgs under a wide variety of driving conditions, from short hops to multi-thousand mile road trips covering sometimes nearly 1000 miles per day of driving.

Sincerely,

Macster.
I stand corrected! Although my reasoning was diesel fuel contains more energy than gasoline because it's denser and we purchase both by volume at the pump.
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Old 11-10-2010, 07:55 PM
  #40  
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If they just reduced the size of the 911 to what it used to be they wouldnt have to do any of this silliness.

When I park my 997 next to my 964, its ridiculous how huge these cars have gotten.

From the 964 point of view, the 997 is a minivan.


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Old 11-10-2010, 08:18 PM
  #41  
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Originally Posted by alexb76 View Post
HOW MUCH I SHOULD EAT MEAT, ....
While not exactly that extreme, my company is moving to a health benefit program that is based on health measurements. Everyone does blood tests once a year and based on results, your premium varies...

So, if you are willing to pay, go ahead and eat and smoke all you want. Maybe it should be the same with cars. Put a polution tax on it, let us pay for it, and get it over with...

-T
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Old 11-10-2010, 08:45 PM
  #42  
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Originally Posted by KirkF View Post
If they just reduced the size of the 911 to what it used to be they wouldnt have to do any of this silliness. When I park my 997 next to my 964, its ridiculous how huge these cars have gotten. From the 964 point of view, the 997 is a minivan.
I wish we could go back too, but that's impossible. If you look at how much weight, in the average car, comes from safety and emissions equipment it's staggering!
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Old 11-10-2010, 09:20 PM
  #43  
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But all cars have gotten bigger. I think some of you guys would rather be driving an Elise.
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Old 11-10-2010, 09:21 PM
  #44  
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Originally Posted by brt3 View Post
I wish we could go back too, but that's impossible. If you look at how much weight, in the average car, comes from safety and emissions equipment it's staggering!
Not only that but also consumer demand for doodads and gobbles of space. One would think that sports cars would be immune to that but just scan pages of this forum and see posts essentially clamoring for more of that nonsense. When someone objects, the std reply is that they can, and should, have it both ways. The reality is that no, one cannot have it both ways - it's an illusion for those people.
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Old 11-10-2010, 10:14 PM
  #45  
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I would love to hear, from a Porsche engineer, how much weight is added to a 911 solely because of safety and emissions gear. And also, how much extra size is required to accommodate said gear.

We are to a point where the biggest gains -- in both performance AND economy -- will come from advances in materials. Several companies seem to be on the verge of price breakthroughs on carbon-fiber or composite materials, and when that happens things will get interesting. Lambo is on the cutting edge of this, as they have a joint research project at the University of Washington that incorporates Boeing's expertise. Their new show car, the Sesto Elemento, is a great example of this, as it's not a Lotus-sized car -- yet it weights 2,200 pounds. A little more than a ton and it has 570 HP!

Now imagine a real-world implementation of this technology in a Porsche. Say we keep the 400 HP output of a GTS, but drop the weight to 2,800 pounds. Sounds like fun, doesn't it?

It's easy to be upset about the issues that seem to be strangling our cars, but we may also be on the verge of new technologies that make Porsches more fun than ever. Case in point: towards the end of the 19th century New Yorkers held a series of meetings to deal with an impending environmental crisis that threatened to shut the city down. The issue? Commerce depended on transportation by horse, and the sidewalks were stacked with horse manure. By the end of the 1890's most people forecast doomsday scenarios that involved shutting the city down. However, none of this came to pass; a technology no one anticipated -- the automobile -- changed the course of history and saved New York City from ecological disaster.

Ironic, ain't it?
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