I was browsing the Auto express today, and was surprised to see they had a test of the Golf MK V GT TDI.

Curious to read this small atricle the first place i loked was price :eek: & spec ,

Spec - 167BHP Turbo Diesel.

Price

Id have to say it all comes down to how long you are going to keep the car - as the MPG disadvantage of the petrol will certainly hinder it.

near on

I drove Dad's old 140hp MkV TDI a fair bit and really liked it. Lots of low down grunt. He now has a GTI and it IS awesome, but 30mpg compared to 50....

Oddly enough, the GTI also has a lot of low down grunt and for something which redlines at 6500 odd, it has surprisingly good 1500-2000rpm pull (uphills, etc)

Oddly enough, the GTI also has a lot of low down grunt and for something which redlines at 6500 odd, it has surprisingly good 1500-2000rpm pull (uphills, etc)

This seems to be a big change to the way petrol turbo's deliver power now - gone are the days when you had to either have a costly twin turbo setup to achieve this, thanks to variable vane and twin scroll technologies

Now all they have to do is sort out the economy and I can get back in a petrol

Chris

In many ways latest technology petrol turbo charging will make the diesel reduntant.

I state this because if 1.4 Turbo petrols can achieve near on 50mpg and push out 140-170bhp (as at today) the technology will develop further with decoupling air con & brake regeneration & stop start tech which will mean high performance petrols will deliver 60mpg and more. At this point diesels will require such a vast milage to claw back the original higher purchase cost - which is set to increase due to the tighter emmissions targets.

I believe currently for a diesel to clawback the higher purchase price your looking at 60,000 miles. The old pros for diesel was the fact you could have a lazy style of driving but really motor on while a petrol needed a bag full of revs this is getting less and less the case.

Ive also read that the lastest R&D (from Autocar source) state that all manufacturers are developing a technology which will mean that petrol will be injected at the same pressure as a diesel and there will be no spark plugs + it will have a large rev range akin of modern petrols - IIRC they predicted this to be mainstream by mid 2012-2015.

Have you seen that stop start - tech has been added to every 5 series BMW bnow... and that the 535d which did have combined of 35 is now 40mpg... and the 530d did have 37 now is 44mpg 525d was 42 is now 47mpg.

I really applaud BMW for this - no other make has made such progress on its current rolling stock. Lets hope they all do asap.

Stop start and brake regeneration are coming onto the MINI range soon , too.

Having done lots and lots of miles in a 140, many in a 170 (both A3s) and driven a couple of VAG 20.T engines I personally would go for the petrol. If you need economy (or it's a company car & emissions matter) then 170 is the one to buy. A much nicer engine to live with than the 140. The stories about lag are untrue IMHO & the power delivery is exceptionally smooth.

An added bonus is if you buy a 170 it normally comes as a better package than the 140 (regardless of badge) & as such you get less wallowy suspension & more gadgets than you would get in the 140

I agree with Welshy though ( :eek: will miracles never cease ), I think petrol technology is catching diesels once more. Originally petrol was way ahead & then it looked like diesel would kill off petrol for a while - the advances just kept coming as manufacturers finally invested heavily at the end of the 90s and the first half of this decade, but now I believe the rate of progress has slowed.

One thing you forget though, Welshy, is the company car market which is priced entirely on CO2 emissions. The vast majority of company cars are, and will remain for the forseeable future, diesel.

A few points here regarding all these gadgets Welshy keeps banging on about:

Stop/start, brake regeneration and aircon decoupling cannot allow an engine to produce more mpg than it's capable of on the extra-urban cycle with the aircon switched off. For that to be possible would be to have discovered a perpetual motion machine! If an engine is cruising at a more-or-less steady speed, then all the extra gadgets do is supply more weight, thus REDUCING economy. Sure, they will improve economy in town, but the near-50mpg figure Welshy's quoting is extra-urban. Therefore, his claim that adding stop/start, brake regeneration and aircon decoupling to a small-capacity turbo petrol will increase the ultimate mpg higher than what can be achieved at present is simply not true. Improvements to actual engine design might, but that's not the same thing. And anyway, there's a school of thought that the only reason car manufacturers are pursuing things like stop/start is that the internal combustion engine is about as far-developed as it ever can be in terms of economy...

Add to this the fact that the laws of physics and chemistry prevent you from achieving economy as good as a diesel from an equivalent petrol engine, because the chemical potential energy per unit volume of diesel is over one-third as much again (~44MJ/l vs. ~32MJ/l). This is why a petrol engine producing around 100bhp will produce 170g of CO2 per 100km, whereas a diesel engine will manage something like 120g/100km. If there's more energy in the fuel, you don't need to burn as much! For people with green leanings, their bio-equivalents are even further apart (bioethanol @ ~20MJ/l vs. biodiesel @ ~34MJ/l) by the way. Therefore, as biofuels get added to fossil fuels in greater and greater quantities (as is already happening), the owners of petrol cars will be at an increasing disadvantage.

I appreciate that the proponents of things like stop/start make very convincing arguments, and in some cases the arguments they're even be true. For instance, if you happen to live in town, and hardly ever go on motorways or A roads, then stop/start etc. will be a bonus for you. But they're not one-solution-fits all. Most of my driving is on motorways, so all this technology would go to waste (especially as the wobble-plate compressor on the Fabia's aircon varies compression and thus drain on the engine according to cooling demand anyway!)

It's just like hybrids - great if you live in town (and therefore achieve rubbish mpg anyway: if you start low, it's easy to go higher), but a severe handicap if most of your driving is out-of-town. This is why the car with the highest ultimate mpg on sale at the moment is (I think) a C1 1.4HDi @ 83.1mpg, whereas the f

Stop/start technology is not new, I am sure a few of you on here remember VW did a Polo back in the 1980's with this technology in it, whilst way ahead of its time, this version sold relatively few numbers compared to its other versions, despite it being pushed a s suitable town car, with its comparably very good MPG, it was let down by its reliability ( :eek: an unreliable VW in the 80's ).

So it appears that BM are resurecting this technology.( Will it be as un reliable as it was the 1st time round ?). IIRC, the improvements of MPG on the petrol Polo were the same as BM are getting on their diesel models. So the only real test wil be if the technology is more reliable, as there apperars to be no / neglible improvements in MPG terms.

As for Biofuels, well the judgement is on hold as far as I am concerned, whist I applaud the potentail savings in emmisions, has anyone thought about 1) the effort required to extract fuel from tthe crop, and 2) when all these fields are growing the biofuel crop, where do we grow the food to eat ? ( cars can be driven for miles and save the planet, but potentially it will be starving people who drive them )

Stop/start technology is not new, I am sure a few of you on here remember VW did a Polo back in the 1980's with this technology in it

Polo Formel E??? :confused:

whilst I applaud the potentail savings in emmisions, has anyone thought about 1) the effort required to extract fuel from tthe crop, and 2) when all these fields are growing the biofuel crop, where do we grow the food to eat ? ( cars can be driven for miles and save the planet, but potentially it will be starving people who drive them )

Not saying biofuel is the ultimate answer either, but adding a 'sustainable' portion to fossil fuels will help fossil fuel reserves last longer, and decrease net CO2 emissions (which I'm sure is pretty obvious). Trouble is, there's not one single solution that will suit everyone's requirements and my point was that BMW's claims regarding their new technology aren't as black-and-white as you'd be led to believe...

Polo Formel E??? :confused:

Thats the one , youre giving away you age

Agreed with the above posts but the reality is that anything which will increase the chance of you running closer to the extra urban target all the better.

On an individual basis this may not mean that much but when you have 100,000 cars suddenly increasing their mpg quite significantly (as we all sit in congestion at some time or another) then it is nothing but a great idea.

I personally think that every car fitter with air con should have solar panals on the roof so that it is fully powered by sunlight & if there is any spare energy this is used to charge up the battery.

Automatic gearboxes should be fitter to all cars - firstly this will eliminate the issue of riding the clutch, 2nd impossible to over rev the engine 3rd it will always change to the correct gear required and it should unless forced run in economy mode.

I dont think engines are reaching their peak yet - all this econess from the brands is due to the fact the motorist wants quick results to cut their car taxes, long term I guess maybe these technologies will continue but with ever more frugal power units.

Automatic gearboxes should be fitter to all cars - firstly this will eliminate the issue of riding the clutch, 2nd impossible to over rev the engine 3rd it will always change to the correct gear required and it should unless forced run in economy mode.

Although cars with automatic boxes tend to be a) heavier, more expensive to build and maintain and c) thirstier than their manual counterparts?

Maybe an R&D project there to solve that though

Chris

True, making a small emissions reduction to a certain proportion of all the cars produced will have a significant overall effect. Welshy's other suggestions are all nice, well-meaning ideas - but also impractical and/or pointless, I'm afraid.

In the case of the solar-powered air con, covering your entire car roof with photovoltaic cells will allow you to produce around 100-150W. Unfortunately, a car's aircon consumes around 1000-1500W so that's a non-starter. The closest thing to that I can think of was a solar cell-filled sunroof that was an option on the Superb(?) that ran fans to circulate air in the car when parked, thus helping to keep it cool for when you got in on sunny days. But an electric fan uses much less power, and the air it circulated was at ambient temperature, not force-cooled.

As for the auto-box, the automatic versions of cars are consistently LESS efficient (on paper, at least) - as Chris has just said, so I'm not convinced by that. Better education of drivers would be more useful here, I think - as is already the case to an extent on the UK driving test.

Maybe there is yet scope for improving the efficiency of car engines, although as I suggested, the fact that car manufacturers are pursuing efficiency improvements in ancillary systems rather than the engines themselves calls this into question. Maybe it's an attempt to balance performance with green-ness, though. After all, if fuel efficiency was the only consideration, the car manufacturers would all be trying to sell us bicycles!

I'd imagine there are certain drivers on here who consistently get 15-20% lower mpg (even when they try to drive economically) than some others through uneconomical driving style, which is always going to be the biggest factor in emissions, fuel economy & component lifespan.

As for the auto-box, the automatic versions of cars are consistently LESS efficient (on paper, at least)

Isn't this mainly due to the use of torque converters? If you had an automatically operated plate clutch and gearbox you'd get a more efficient automatic.

Rob.

Isn't this mainly due to the use of torque converters? If you had an automatically operated plate clutch and gearbox you'd get a more efficient automatic.

Rob.

Quite possibly, but I think Welshy's argument hinges on the fact that the torque convertor helps keep the revs down. My mum's Jazz has CVT, which is yet another auto 'box possibilty. Still less efficient than the manual, though. (Although only by a fraction, and under the lab conditions that mpg figures are worked out...)

Quite possibly, but I think Welshy's argument hinges on the fact that the torque convertor helps keep the revs down.

You'd just program the automatic gear selector to change up at lower revs...or even better, at the most efficient point.

Rob.

For maximum efficiency shouldnt the engine be reving at peak torque?

If that is the case (which I believe it is) then shouldnt all automatics be constantly variable to ensure engine revs are maintained at that level.

Is this not how train engines work - set the engine to max torque output and just holt it at those revs (in simple terms).

True, making a small emissions reduction to a certain proportion of all the cars produced will have a significant overall effect. Welshy's other suggestions are all nice, well-meaning ideas - but also impractical and/or pointless, I'm afraid.

In the case of the solar-powered air con, covering your entire car roof with photovoltaic cells will allow you to produce around 100-150W. Unfortunately, a car's aircon consumes around 1000-1500W so that's a non-starter. The closest thing to that I can think of was a solar cell-filled sunroof that was an option on the Superb(?) that ran fans to circulate air in the car when parked, thus helping to keep it cool for when you got in on sunny days. But an electric fan uses much less power, and the air it circulated was at ambient temperature, not force-cooled.

As for the auto-box, the automatic versions of cars are consistently LESS efficient (on paper, at least) - as Chris has just said, so I'm not convinced by that. Better education of drivers would be more useful here, I think - as is already the case to an extent on the UK driving test.

Maybe there is yet scope for improving the efficiency of car engines, although as I suggested, the fact that car manufacturers are pursuing efficiency improvements in ancillary systems rather than the engines themselves calls this into question. Maybe it's an attempt to balance performance with green-ness, though. After all, if fuel efficiency was the only consideration, the car manufacturers would all be trying to sell us bicycles!

Ok so on the solar panals according to your numbers the power that can be generated is 100-150W but the air con requires 1000-1500W. This to me means only one thing they need to make the air con run on less power - make it more efficient.

If using solar power & the necessary R&D to create a 150W car air con work is too high then using breake regeneration power is the clear answer, why waste all this kinetic force - have it charge up a 2nd or larger battery to run the air con exclusively.

With the education of drivers - you always going to have vast differences between drivers as at the end of the day noone is the same. You could argue that anyone over 15 stone shouldnt get in the car or if your not carrying passengers take out the back seats.

Just thought of another simple way - tyres, clearly first everyone should ensure they are inflated correctly but after that tyre makers should be making them with less rolling resistance while still maintaining braking & cornering grip levels.

Is this not how train engines work - set the engine to max torque output and just holt it at those revs (in simple terms).

It works that way on trains, as they tend to work on a diesel-electric basis. It's also how a CVT automatic works. Whether it'd work like that for a torque converting auto 'box, I'm not sure. Don't see why not, though...

Thought of another point - weight.

Oil - we use 4.5ltrs in the engine surely that can be decreased

Fuel tanks - car makers could reduce the size of their tanks and by doing so will instantly increase the ave mpg of said car.

Coolant - there should be much smaller radiators & much more efficient cooling.

Also when the engine is cold the grill should close so that the engine get up to temp much quicker and then opens once correct operating temp is reached.

What do you think?

First three are a bit daft - you'd be saving a few kilograms at most. The last one is already done by BMW. Seems a bit gimmicky to me (bit of a common theme for me and BMW 'innovations'), but they must believe it makes a difference...