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2007 Volvo V70

17 messages,  Last post on Aug 29, 2007 at 5:41 PM

You are in the Volvo V70 Forum.

What is this discussion about? Volvo V70, Automotive News, Wagon

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#2 of 17 Re: 2007 Volvo V70 review [andrei3] by fedlawman

Feb 05, 2007 (5:28 pm)

It's very handsome, but if it drives like the new S80 it's based on (yawn), I'll just keep my 2004.

#3 of 17 Re: 2007 Volvo V70 review [andrei3] by jrcosmo

Feb 11, 2007 (7:42 am)

i hope they offer this with diesel that meets new US emission stds so that even if not offered in US, we can order for Euro delivery and bring in.

#4 of 17 Re: 2007 Volvo V70 review [jrcosmo] by v70norway

May 16, 2007 (1:44 pm)

Replying to: jrcosmo (Feb 11, 2007 7:42 am)
Greetings from Norway.
 
We have the diesel model, just one week old. So far we have had two breakdowns, battery totally flat both times. When we first picked up the car, the dealer advised turning the ignition on so that all lights (airbag, fuel etc) were showing, waiting until the lights went off, then turning over the engine. Today we were stuck on a ferry and had to stay on board for two more crossings whilst the crew jump started our totally flat battery - my husband had turned the ignition on for a whole 3 minutes before turning over the engine! Hoping to get to the bottom of what is a really ridiculous problem to have in a brand new car.
 
Were told by fellow passengers who have diesel motors that the battery needs to be much stronger than the one sold with a new Volvo. Will keep you posted on what dealer says!
 
Other than that very happy with the car, fantastic ride, and given that we have the 2.4D 126 horsepower model, it still has plenty of power for suburban driving.

#5 of 17 Re: 2007 Volvo V70 review [jrcosmo] by jim314

Jun 09, 2007 (12:41 pm)

Replying to: jrcosmo (Feb 11, 2007 7:42 am)
It is my understanding that you cannot import the Volvo diesels into the US even through European delivery, because that model is not qualified for sale in the US. Some unqualified vehicles are imported if they are individually retrofitted, which would be prohibitively expensive. And I don't think the Volvo diesels are currently qualified for US sale. If they were, they would be selling them here, they would probably go like hotcakes. (If I am wrong on this, then I apologize in advance for making a claim that I haven't recently researched. I inquired about this and was told it couldn't be done. Despite what I write below, I am attracted to diesels and imagine I would enjoy owning one.)
 
I have thought about diesels for a long time but have always just bought gasoline engined vehicles because they are cheaper and have always had lower tailpipe emissions.
 
The biggest single factor in the higher mpg obtained with diesels is that diesel fuel is about 17% denser than gasoline. A liter, or a gallon, of diesel fuel weighs 17% more than the same volume of gasoline, so it contains 17% more fuel, and carbon. It is the weight of fuel consumed and not the volume of fuel consumed which determines the level of tailpipe emissions of carbon dioxide. On a weight basis diesel fuel and gasoline release almost exactly the same amount of heat energy. The diesel cycle, however, converts somewhat more of this heat into mechanical power.
 
Then there are the problems of NOx and fine particulates. Diesels are somewhat more efficient than spark ignition petrol engines, but one way they achieve this is by pumping a lot more air through the cylinders per unit weight of fuel. This causes more NOx than spark ignition engines in which the air is of necessity "throttled" to keep the fuel-air ratio in the range where a spark can ignite it.
 
Modern diesels from VW and Mercedes are much, much cleaner, but this is being obtained by the use of special emissions controls systems which add to the cost and slightly reduce the efficiency.
 
Another way that diesels improve their apparent efficiency over gasoline engines is that the diesel option is usually of lower horsepower than the gasoline option. A gasoline engine of the same max power rating as the diesel would usually have higher efficiency than the higher power one offered.
 
The true efficiency advantage of the diesel may not be enough to justify the higher lifecycle cost of purchase and maintenance. I say "may be" because I don't know enough to have a professional opinion on this question.
 
But my nonprofessional opinion is that when comparing diesel mpg to that of a gasoline engine you ought to divide the diesel mpg by 1.17 for a true comparison based weight of fuel consumed. (Or multiply the L/100km value of the diesel by 1.17.) I know fuel is sold by volume, but if diesel and gasoline were sold on a equal heat of combustion basis, then a litre or a gallon of diesel would cost 1.17 times the same volume of gasoline. Someday this may be the case.

#6 of 17 why compare on weight? by jurrasicsailor

Jun 21, 2007 (8:39 am)

Jim your arguments make no sense. Seems like you are really searching to find some way to ding the diesels. Fuel is sold by volume. If you are unhappy with mpg numbers, then do it by mile per dollar of fuel, or something that actually matters. your choice of density as the comparison point also makes no sense because it changes with temperature, which is why gas stations have converstion charts as they purchase at temperature -specific rate. You also completely ignore torque, which is probably the more important engine spec in terms of usability. There modern high pressure injection turbo diesels absolutely crush a gas engine of similar displacement. If you want to equalize for a more fair comparison, use torque as the basis. IN ANY CASE, modern diesels are a much more economical choice.

#7 of 17 Re: why compare on weight? [jurrasicsailor] by jim314

Jun 21, 2007 (9:57 am)

Replying to: jurrasicsailor (Jun 21, 2007 8:39 am)
Volume is a more convenient and cheaper way to meter out a liquid, but from the point of chemistry and engineering it is the weight of fuel which is the true measure of the amount of fuel. In commercial airline and marine shipping fuel is priced and recorded by weight.
 
In chemical reactions (like combustion) there is a law of conservation of mass, but there is no law of conservation of volume.
 
You bring up fact that the density of fuel changes with temperature. It does so because the volume changes with temperature. The mass of a given amount of fuel does not change with temperature.
 
The output torque and power of an engine/tranny combination is what is important, not the maximum torque of the engine itself. The output torque from the tranny can be increased by changing the gearing. But the maximum rated power (HP rating) of the engine/tranny combo cannot be changed--the engine can only develop so much power. A transmission can multiply torque but cannot multiply power.
 
Diesels have some advantages over gasoline engines
 
(1) The diesel cycle is somewhat more thermodynamically efficient on a mass basis, the only true basis for comparison.
 
(2) Diesel fuel is less flammable than gasoline
 
(3) The diesel exhaust stream is significantly lower in temperature than that of a gasoline engine so turbochargers in diesel engines have much less heat stress.
 
I like diesels, but I don't think the sellers of diesels should get away with misrepresenting the extent of the efficiency advange of diesels over gasoline engines.
 
PS Another reason for the superior efficiency of current diesels over current gasoline engines is that the diesels are direct injection (i.e. fuel sprayed directly into the cylinders) whereas nearly all gas engines use less efficient port-injection. When more gas engines use direct injection the diference between gas and diesel will be even less.

#8 of 17 Re: Direct fuel injection [jim314] by jim314

Jun 24, 2007 (11:35 am)

Replying to: jim314 (Jun 21, 2007 9:57 am)
On the other hand it could turn out that for gasoline (spark ignition) engines that direct injection will not be widely worth the extra complexity and expense.
 
Modern very high pressure "common-rail" fuel systems with piezeoelectric injection has really improved the combustion process in compression ignition engines. The fuel is evidently injected in up to 5 separate injections in each power stroke. This smooths out the energy release and improves efficiency.

#9 of 17 Diesel Horse Power and Torque by flipper6

Jun 29, 2007 (7:15 am)

Jim,
 
I am no scientist but I believe your comments about measuring weight of fuel makes a lot of sense. I am confused by your comment that the torque of an engine (stand alone) is not relevant but rather the engine/tranny combination. If that were true, why do manufacturers publish the torque of an engine and not the engine/tranny. Furthermore, if horse power was the only relevant measurement of power, why are trucks that are used for towing, not using high revving high horse power engines. I believe that they go for large displacement, high torque engines regardless of the gearing. I have no scientific proof but something tells me that the torque of an engine is still relevant.

#10 of 17 Re: Diesel Horse Power and Torque [flipper6] by jim314

Jun 29, 2007 (5:37 pm)

Replying to: flipper6 (Jun 29, 2007 7:15 am)
I didn't mean to say that torque is irrelevant, but simply that, in my opinion, it's a bit of a shell game to make a big deal about the fact that diesels develop higher maximum torque relative to their their own max horsepower than gasoline engines do. The higher torque value of the diesel is eye-catching, but they don't mention that the diesel engines have a much lower max rpm value. If they do mention it, they treat it as almost a postive, which it is not. If engine A does not make useful torque above 4000 rpm, but engine B makes useful torque up to 6000 rpm, then engine B needs a simpler transmission. The Volvo diesels work significantly better with the 6-speed manual, but the gas engines work fine with a cheaper 5-speed manual.
 
At any given rpm the relationship between power and torque developed by an engine is Power in hp = torque in lb-ft x rpm / 5252, in metric units Power in kw = torque in Nm x rpm / 9549. The whole torque curve is extremely useful information about an engine, but its main use is for the purpose of selecting the transmission gearing. This is something that the manufacturer does--if it's done right then the vehicle performs well whether its powered by a petrol or a diesel engine.
 
For the V70 compare the engine specs for the two Volvo 2.4L diesels (120 kw or 161 hp and 136 kw or 182 hp) and the Volvo 2.4L normally aspirated 168 hp gasoline engine (125 kw petrol), and ask yourself whether the much greater cost of the diesels would be worth it to you. Go to http://www.volvocars.co.uk/models/v70/techSpec.htm and compare the two diesels with the 125 kw (168 hp) petrol engine. Note that the mpg values are mpgUK. Divide mpgUK (mi/Imperial Gallon) by 1.2 to get mpgUS. From the acceleration (0 - 62 mph) youcan see that it is power not torque which determines the capability of the vehicle under ordinary circumstances.
 
I believe that the diesels are better designed and built engines than the petrol one, and they use about 13 % less fuel per unit distance (fuel measured by weight, the true basis of amount of fuel, diesel fuel is about 17 % denser than gasoline) than the petrol engine, and produce about 19% less CO2 emissions per unit distance ( diesel 179 g/km vs 220 g/km for the petrol engine). But the diesels cost a whole lot more in initial outlay and maybe in maintenance costs over the life of the vehicle.
 
Large diesels in commercial trucks are designed to operate at a very high fraction of maximum rated power and to be very fuel efficient with a very expensive transmission with many gears. In my opinion, the average private vehicle owner doesn't make strong enough demands on their vehicle to justify the extra cost of a Volvo diesel. But if you put a lot of miles on the car, drive at very high speed or tow a heavy trailer then the diesel might be cost effective.
 
Or maybe you just want the diesel and money is no object.

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