Maintainable diesels

Hmmmm..I'm not sure if you're quite up to speed with the modern diesel thing but they're far more likely to please Jeremy Clarkson than the green lobby! Take the Fiat 2.4JTD (as installed in Alfa 156/9) in rough figures:

Can you spot the pattern? I'm sure Fiat are not alone in this respect.

I know how you feel. I didn't realise how totally rubbish my Astra reliability was until I bought an Alfa Romeo!! Almost 5 years without an AA call out where the Astra got visited annually by them. I don't feel any need to go near a Vauxhall showroom these days and that's after being a customer for 13 years.

True, but you fully exploit the power of each of those in turn and note the fuel economy figures returned :-)

AstraVanMan ( snipped-for-privacy@whataloadofforeskinbollocks.co.uk) gurgled happily, sounding much like they were saying :

True, but to maintain the same progress you'd have to pedal "Car X" with

Of course, in the real world, we all know that power is like money - you fully exploit what you have available...

Now there's a tricky one to think about!! My guess is that since the hp improvement, in these cases, came via more efficient fuel burning all you do is pour badly burnt fuel into the exhaust in the 136hp version while converting it to power and heat in the 200hp one.

The urban and extra-urban figures also stay very similar through this era (32mpg and 52mpg IIRC) so I'm inclined to think that there will be little difference in fuel economy regardless of driving style from car to car. Had there been a dramatic drop in the urban figure, I would have leant towards your argument but there hasn't.

Anyway, until I get a 200hp one, I'm guessing..

It's more like the bigger HP one gets more air (eg by more boost on the turbo), so they can stick more fuel in to get more power. It won't be more efficient fuel burning. (It may also be that they've also improved the burning to allow it to burn more efficiently at higher fuelling, so they've let the engine do it where before it wasn't allowed to. But more air will be the significant change.)

Isn't the fuel economy figure rather independent of driving style - which I suspect was Adrian's point. Get the faster one, it'll encourage you to boot it more, so in real life economy will suffer while you have more fun.

cheers, clive

Clive George ( snipped-for-privacy@xxxx-x.fsnet.co.uk) gurgled happily, sounding much like they were saying :

Exactly.

The same power is required on each of the standardised tests, for "Car X", because the same "manouvres" are being done. Except the 136bhp may require half throttle, while the 200bhp only uses one third. So if you "drive according to the tests", you aren't using the extra power.

But drive 'em both at half throttle, and watch the difference in fuel. Or drive both hard...

My current Range Rover is 300kgs heavier than my old one. It has 185hp as standard compared to 112. Yet the fuel economy is about the same despite the older one being manual transmission and lacking in power and torque. Even more significant is that the new RR, which has a BMW 3.0 engine, is more economical when the power boosting performance chip is fitted than without. It is about 3mpg more economical on average fitted with the chip which is set for a fairly mild performance boost, around 20hp I suspect.

Huw

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Clive George" saying something like:

It will be. Modern high pressure injection systems provide a much greater surface area for fuel combustion as the droplet size is much smaller, thus allowing more power to be developed from the same amount of fuel.

If 'twere the case, the mpg would go up - and it hasn't.

Yes, a modern high pressure injection system is more efficient than the older ones - but the engine we're talking about isn't one of the older ones, it started out in the appliciation we're talking about with a modern high pressure injection system.

cheers, clive

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Clive George" saying something like:

The combined test being an average of sorts, it wouldn't really show much of an improvement unless things were drastically different. I'd suspect though, that higher engine speed economy is better on the later engines.

Gradual improvements, tinkering with the fuel delivery pressures and boost settings, allied with improved engine mapping, plus internal improvements - better bore sealing, better gasflow characteristics.

Maybe a little bit. Not 200BHP vis 136BHP worth though.

And most importantly, letting the turbo generate more boost - which is responsible for the vast majority of the power gain. The efficiency may be ever so slightly better, but the higher power engine gets it mostly from being able to burn more fuel in the increased air available.

cheers, clive

Although, in this particular application, the injectors (unijet to multijet) and head (10V to 20V) were the significant changes that Alfa boasted about since production started.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Zathras saying something like:

Oh well, there you go, then. Both changes certainly significant enough to account for a substantial power increase.