Car mpg question

and the horrific costs when they break.

Not quite so much better if you get direct injection SI.

Run out of go at 4500 rpm. So have very long gearing. A long gear reduces the torque at the wheels.

Bet you can't find a 1.4L Diesel comparable to the 125bhp 1L Ford Fiesta.

Or any Diesel under 3L comparable to 313bhp the Ford 2.3L ecoboost makes.

Utter nonsense so long as you compare normally aspirated SI with normally aspirated Diesel (remember them asthmatic pieces of junk?) and Diesel turbo with SI turbo.

The best specific power they have got from a production turbo diesel is about 100 bhp/L using very expensive sequential turbos. SAAB TTiD

95bhp/L and Opel/GM bi-turbo 100bhp/L. There have been many SI turbo petrol engines in production cars making around 140bhp/l and some performance models with 200bhp/L. Even Ford can crack 125 bhp/L in the 3 pot 1L Fiesta and 136bhp/L with 2.3 ecoboost (about 10 and 15 years late as Nissan made 250bhp 2.0 SR20DET in 1999 and 280bhp SR20VET in 2001).

Dave Plowman (News) brought next idea :

Well, a badly maintained diesel didn't ought to be on the road. Mine is well maintained and indistingusable from a petrol on the road. I can smell a petrol car, there is no smell from my diesel.

Peter Hill submitted this idea :

It is only fair to compare like with like. I think we are discussing basic diesel and basic petrol.

bhp/l is only a part of the story. My previous car was a 3.5L petrol, my present one is a 2L diesel, both bought as tow cars. The sheer grunt and relaxed power delivery of my 2L diesel makes it a better tow car. The petrol did a best of 27mpg, I easily see 50mpg from the diesel and have managed over 60mpg.

Have you sniffed the exhaust when booting it for overtaking or just simply accelerating?

All exhausts seem clean from the owner/driver's POV, not necessarily so from the view of following traffic.

Tim

Nowadays I only notice a very occasional petrol car by its smell, usually only if its cold and just started or if it is something pre cat.

By comparison the smell from diesels is about ten times as common, and the clouds of smoke when they are 'regenerating' the dpf is ridiculous.

Tim+ explained on 07/02/2017 :

Obviously not!

I keep an eye on my mirrors and have never seen any soot or smoke behind. Soot on a bumper is a good indicator..

Have you ever walked along a busy street? There must be an awful lot of badly maintained diesels out there. I don't have a particularly acute sense of smell but notice it every time I go out for a walk here in London. Only time I ever notice any smell from petrol cars is at an old car rally.

Did both cars weigh the same? The same type of gearbox, etc?

What 3.5 petrol engine are you talking about? The difference in MPG suggests you are talking about an ancient petrol engine versus a modern diesel.

BTW, my 35 year old Rover SD1 3.5 does better than 27 mpg at best. It would be much better with a modern gearbox too.

Quite. Even in heavy London traffic you can usually smell the diesel car in front of you. Not always - but it's very common.

I agree, there are and believe something ought to be done about them. Many of them on the high street, are the buses. Our local bus service use a modern diesel/ electric, which are much better.

You need a pretty heavy smoker to deposit much soot. Looking in you mirrors whilst accelerating is a poor guide although doing this at night with another car's headlights illuminating your exhaust can be considerably more enlightening.

Basically, sitting behind the wheel is a terribly bad way of judging your own car's emissions.

Tim

The MPG on mine goes shooting down when the DPF burning starts.

Not these ones I hope.

Tim

Tim+ submitted this idea :

No smoke marks on the white caravan either.

The MOT smoke test usually comes in at (from memory) < 1/10 of what is permitted.

Tim+ explained :

Er, no - I don't live anywhere near the 'smoke'. Our local buses seem to work very well indeed. The diesel shuts down when the bus comes to a stop, they pull away on electric, then the engine starts once second gear is selected. The diesel seems to also kick in when I guess the battery power runs low.

Visible soot is only part of a diesel engine's polluting output.

Tim

I suppose the battery failures those buses suffer, might be due to congestion they suffer in London / miles covered per hour. Our local bus runs a 20 mile route, City to outlying town, via several villages including my own and timetabled to be covered in 70 minutes.

That type must be a wonderful relief to anyone who is unfortunate enough to live close to a bus stop. I was very pleasantly surprised when I first noticed a bus doing what you describe, although it was a slight disappointment not to have that rattling lump at the back blowing that 'engine room' smell out of the side.