VW TDI Secret?

[Conceptual]

Can anyone explain how the VW 1.6L TDI can achieve 50+MPG while others can barely crack the 35MPG mark? Is there something special about the motor that adds to this efficiency?

Any and all info is GREATLY appreciated!

Chris

[Jersey Tom]

Is it diesel? If so, there's your answer. There's no magic to most consumer car engines. Diesels add fuel efficiency, as do lightweight or aerodynamic cars. Power output as well, but it really comes down to how much you use.

Bottom line, it takes X amount of power to accelerate a car from rest. Heavier car, takes more power. Requires Y amount of power to keep a car moving at highway speed. More aerodynamically efficient, less power. Big powerful engines its easier to demand excessive power from. Smaller ones may also be intrinsically more mechanically efficient particularly at low revs.

But a lot of it comes down to driver. For what it's worth, I can get 30 MPG in a 300hp Nissan 350.

[Conceptual]

It is a diesel, but here is where I get lost.

The 1.6l VW TDI gets 50mpg while the Audi 1.8l TDI gets 30mpg. I understand the displacement difference counts for SOME, but .2L can't possibly lower efficiency by 30%, can it?

Thanks! And the 2004 Nissan 350Z is a very fun car to drive and not really that bad on gas (from what a close friend that owns one tells me). I really like that car, but in the end, it is much more than I need to move through life. And it doesnt seat my 6 person family!

Chris

[zac510]

Aren't they in completely differnt cars?

I'd expect the Audi to be heavier too, being the 'luxury' marque.

Are you comparing the correct UK gallons and US gallons too?

[millerjam]

You've really got to look at what car models the engines are used in and also how they've been mapped. Also there could be an inherent difference in the companies commercial strategies, for example Audi customers might not be too bothered about fuel consumption...
Anyway I found this article on the VW Bluemotion Polo which might shed a bit of light on VW's strategy. It's a bit politcal I'm afraid but it's still an interesting read:

http://www.telegraph.co.uk/motoring/mai ... polo12.xml

[Conceptual]

You've really got to look at what car models the engines are used in and also how they've been mapped. Also there could be an inherent difference in the companies commercial strategies, for example Audi customers might not be too bothered about fuel consumption...
Anyway I found this article on the VW Bluemotion Polo which might shed a bit of light on VW's strategy. It's a bit politcal I'm afraid but it's still an interesting read:

http://www.telegraph.co.uk/motoring/mai ... polo12.xml

Good article! And the political background noise is kinda relevant, since it points out rediculous discrepancies between exemptions.

Thanks!

Chris

[ReubenG]

The laden mass of the a VW Polo (assumed the hatchback) is 1640kg, vs 1955kg for the A4. I got these off http://www.um.co.za/specifications and they're both for the 1.9Tdi engine, which is what they are usually available in South Africa with - the difference would obviously be bigger if the smaller 1.6 engine was fitted. The 18% difference in mass is probably the biggest culprit in efficiency differences.

BTW, the fuel consumption / economy figures listed on those pages are in units of litres per 100km - here's a nice link to convert to mpg http://www.calculateme.com/cGasMileage/ ... mtoMPG.htm.

[WhiteBlue]

It is important to note the difference between UK mpg and Us MPG. The VW Polo spec was based on UK figures.

There is certainly no secrete to the VW models. Your typically get more than 50 US mpg out of modern diesel powered hatchbacks.

BMW 1 series goes on sale in the US soon and it's 2L turbodiesel 118d model will give you 52 mpg for a five door hatch doing 122 mph including air conditioning, wide tyres and luxury interior with a ton of electric operated functions.(manual gearbox tho).

You have a bunch technologies in there like automatic engine cut off and restart, brake energy recovery, good engine efficiency, electric pumps, electric aircon, radiator aero management and electric steering.

[Ted68]

I wish we were to have the diesel option on the BMW 1-series here. The only versions we get are the 128i or 135i in coupe or cabrio. If they were to sell the 118d here, there would be a blue coupe in my garage. So I guess my next car is an Aprilia...

[WhiteBlue]

http://blog.wired.com/cars/2008/03/bmw-118d-wins-w.html

very interesting read. probably ist the suphur rich diesel that you still have in the US that stops the modern turbo diesels in the US. That issue is in hand but still it may take until 2010 until the 500 ppm sulphur in the US is down to 15 ppm all over the country.

http://auto.howstuffworks.com/how-clean ... works1.htm

You can't blame BMW and VW that they don't want a bunch of customers showing up with sulphur poisoned catalytic soot converters demanding foc replacement.

[Belatti]

The laden mass of the a VW Polo (assumed the hatchback) is 1640kg, vs 1955kg for the A4.

Wow!!!

I have got this car:

GOL 1.6 gasoline engine, 5 door version and weights 947kg according to the owners manual.
I think that South-American GOL is the equivalent of POLO in Europe...

Where are those extra 700kg in the polo? Is that diesel engine 700kg heavier?
Can a couple of extra airbags and a bunch of electronic features weight that much?

[ReubenG]

Firstly, the mass I quoted was the laden (i.e. full tank of fuel + driver + passengers) - the unladen (or licensed mass on the page I quoted) for a VW polo is 1129 kg. So a difference of about 190 kg to the 947 kg figure you quoted. I noticed from the photo you posted that we're probably comparing different year models of the Polo and different specifications (i.e. air-con, power steering etc which all add up).

What I would consider more important from the source of my information was that according to their figures, the Polo 1.9Tdi gets 4.9 l/100km vs the 6.6 for the A4 1.9Tdi - most of these figures are determined independently in South Africa by Car magazine and they are pretty reliable. Using the calculator I linked, this gives consumption of 48 mpg (US) for the Polo and 36 mpg for the A4 - close enough to your figures of 50 and 35.

Also bear in mind that in SA diesels have a different map to European spec engines as low sulphur diesel is only available in certain areas.

[Conceptual]

Firstly, the mass I quoted was the laden (i.e. full tank of fuel + driver + passengers) - the unladen (or licensed mass on the page I quoted) for a VW polo is 1129 kg. So a difference of about 190 kg to the 947 kg figure you quoted. I noticed from the photo you posted that we're probably comparing different year models of the Polo and different specifications (i.e. air-con, power steering etc which all add up).

What I would consider more important from the source of my information was that according to their figures, the Polo 1.9Tdi gets 4.9 l/100km vs the 6.6 for the A4 1.9Tdi - most of these figures are determined independently in South Africa by Car magazine and they are pretty reliable. Using the calculator I linked, this gives consumption of 48 mpg (US) for the Polo and 36 mpg for the A4 - close enough to your figures of 50 and 35.

Also bear in mind that in SA diesels have a different map to European spec engines as low sulphur diesel is only available in certain areas.

Where does the 12MPG extra come from in the VW??? A simple engine map?

Chris

[marcush.]

there are alot of holes where efficienc disapears:

bigger car ,bigger crosssectional area-more drag
more electrical consumption for the bigger car(think of all the actuators moving seats ,mirrors,door locks,servopumps (polo might already use EPS) that may actually not be installed but available as options,so you need to carry a big alternator to cover those 200somethings Amperes
static you might need in worst case conditions.
Then you drag along a lot of additional friction through wider tyres + you got more rotational inertia to accelerate (bigger brakediscs,wheels,maybe gearbox internals ,axles driveshafts if it´s a quattro...),then of course the Aircon,wich is also sapping efficiecy ,more so on the bigger car wich does surely not carry the same compressor...
so,in all alot of reasons why the bigger car has not only have to carry the shear extra mass but also the consequences of that extra mass to add up to the worse mpg.

[macro820]

If their cars are like the Audi race cars they do a couple of things different... VERY high pressure fuel injection 1600 bar, they do two different injections into the same cylinder, one at near top dead and another after that little bit is being burned and they have a special cylinder head with a vortex cone on the top which swirls the air and fuel together very efficiently. The diesel car's engine will be a heavier than a gas because the gas engine can be made of aluminum but most diesel car's engines are made of steel to handle the higher compression. I'm surprised no one has said this.. Hope it helps