Diesel Power

[ChrissyBoy]

Just to balance the debate a little....

There's been a great deal of nonsense spoken about diesel performance lately... Yes they have oodles of low down torque, yes they are probably quicker in the real world. But BHP speaks volumes - whoever reckons that a 320CDI could murder a BMW 330Ci has never been up against someone who's really trying. Having road tested an E320CDI then gone straight back into my old 330ci, I can tell you, without a shadow of a doubt the 330 felt like a rocket ship once wound up. Diesels tend to have tons of "shove", but run out of breath early and hence suffer in the all important 0-100.

Anyone ever see the top gear episode where they pitted a 330d against a 330i?

 

[GrahamC230K]

Anyone ever see the top gear episode where they pitted a 330d against a 330i?

No, but would have liked to. With the 330i having the better performance figures on paper, I guess on a 0-whatever sprint it would prove it.


I think you have better get your flame proof clothing on though! .......................

 

[Richard W]

There's arguments for both sides - I went to give moral support to a friend who was buying a second hand car for the first time in 15 years on Friday. It happened to be a 330i Cabriolet....

After we got back to my house he let me have a blast in it and my opinion was that yes it was fast once you'd got it 'on cam'. But low down it just didn't feel £16k more 'special' than my 320d and as the 330 was showing 12mpg when I was hooning about in it I'd rather have a good diesel and a fraction of a second less 0-100

BTW I do remember the Top Gear test - conclusive on the track but not as much as you'd expect!

 

[marcos]

In real world driving the diesel will be quicker but of course round a track the petrol is going to come out on top. You don't have any lag, pulls strongly into the red and is of course lighter. But the difference is minimal and what would you rather do, thrash the nuts out of a car all the time to really move or wallow along in relatively low revs moving at about the same pace as someone thrashing their petrol car?
There are arguments for both sides but as a convert to diesel I know what I would rather have for every day driving.
I find a big diesel very relaxing to drive but a few years ago I may well have preferred a thrashy petrol car, each to their own, as they say.

 

[Shude]

moving to the engine section!

 

[GrahamC230K]

moving to the engine section!

Knew you would say that, but thought it more motoring banter than a specific engine question!?

 

[GrahamC230K]

Whilst on the subject, there is one other element that makes me laugh on the "performance diesel" debate.

All the diesels that come any where close to bettering there petrol rivals have one little advantage.

They have a TURBO!!

Hello, go faster device is cheating no?? Of course it's going to have SOME go to it with a turbo slapped on!!!!

Next time, picture the petrol car in the petrol vs diesel equation with a turbo too and see who wins!!

Just seems like comparing a bannana to a circle to me.

Anyway, each to their own. Looking at fuel prices today as my weekly tankfull fill up seems to increase in cost weekly too, it seems diesel and unleaded is much of a muchness now cost wise.
I only feel sorry for those in M3's and Jap performance cars as Optimax is 88.9 pence at my local Shell!!!

 

[ChrissyBoy]

Whilst on the subject, there is one other element that makes me laugh on the "performance diesel" debate.

All the diesels that come any where close to bettering there petrol rivals have one little advantage.

They have a TURBO!!

Hello, go faster device is cheating no?? Of course it's going to have SOME go to it with a turbo slapped on!!!!

Next time, picture the petrol car in the petrol vs diesel equation with a turbo too and see who wins!!

Just seems like comparing a bannana to a circle to me.

Ok, but what does Kompressor mean?

 

[ChrissyBoy]

There's arguments for both sides - I went to give moral support to a friend who was buying a second hand car for the first time in 15 years on Friday. It happened to be a 330i Cabriolet....

After we got back to my house he let me have a blast in it and my opinion was that yes it was fast once you'd got it 'on cam'. But low down it just didn't feel £16k more 'special' than my 320d and as the 330 was showing 12mpg when I was hooning about in it I'd rather have a good diesel and a fraction of a second less 0-100

BTW I do remember the Top Gear test - conclusive on the track but not as much as you'd expect!

The 330 cab has loads of extra weight over the saloon/coupe, so probably not a fair comparison. You're also ignoring some of the fantastic qualities of the 3.0 straight 6- gorgeous sound, smooth as silk and oh yes - economical - 45mpg on a very long run at 60mph (driving like the pope). It didn't win the engine of the year 2003 3.0L category for nothing.

Also I seem to remember that the 330i petrol absolutely spanked the 330d on the Top Gear test - considering that Jenson Button came off the track with the petrol and still won by some margin.

I'm not trying to aggravate, simply trying to balance the debate by suggesting it's horses for courses. Petrol is still king of performance - get some perspective guys. Of course a 320CDI is going to spank a 150BHP Golf GTI - the Golf GTI isn't really a sports car - but try the same trick with an EVO VI or a WRX. Subaru ain't going to fit oil burners to their WRX.... yet.

 

[Shude]

Ok, but what does Kompressor mean?

if we cancel forced induction from the equation it means that a 2.3 litre petrol is of similar performance to a 3.2 litre diesel.

As has been previously stated, the diesels are great once they get going, but the 230k petrol engine is great from tickover!

 

[GrahamC230K]

Ok, but what does Kompressor mean?

Supercharged.

Last time I checked, not many diesels have them nor does a 330i

You make a good point though. I would not compare my 2.3 to a 320 or 323 (2.5l) BMW. Comparing normally aspirated to forced induction is just not fair when dealing with like engine capacities, hence my point about comparing turbo diesels to normally aspirated petrol cars.

Not sure where you thought I was disagreeing with you?

PS. Is there a reason you don't see Supercharged Diesels?

 

[Shude]

PS. Is there a reason you don't see Supercharged Diesels?

This is something that I wondered about as well!

 

[GrahamC230K]

This is something that I wondered about as well!

Come on Dieselman, I know you will know!!!??

 

[fuzzer]

Mazda did a 626 supercharged diesel.

QED . They don't do it any more

 

[ChrissyBoy]

And I'm going to join the list of curious people too.

Also, given the issues with turbo lag why not just supercharge? Extra mechanical friction? Which is better?

Graham - I was merely pointing out that your beast is supercharged which is comparable to turbo charging, at least in performance terms.

 

[MattEly]

Evenly Balanced!!!

Interesting thread - I have the (S211) E320 CDI & my partner has a C240 - both are great to drive, the diesel (my first by the way) just seems effortless all the way - never seems to have to work to deliver what's needed, but I have to say there is a real buzz listening to the engine sound of the V6 240 - it really is sweet. As you say, horses for courses.

Cheers

Matt.

 

[Dieselman]

Come on Dieselman, I know you will know!!!??

Because superchargers are inefficient compared to turbos. A supercharger saps energy from the engine to drive the charger, a turbo uses waste exhaust gas only, so uses less energy.

Really the question is why do petrols use a supercharger and not a turbo.
A turbocharger increases the output only when required. A diesel engine runs lean at all times other than full power, and also has no throttle to restrict airflow.
On petrol engines turbocharging causes drastic outputs from no boost to boost conditions so is either somewhat undriveable with decent boost or not very effective with low boost.

In addition the throttle on a petrol causes lots of lag as the airflow through the engine is restricted when shut, as this stalls the turbo, on a diesel this is not lag, simply low boost.

Also a diesel has more low down torque so can cope without turbo boost, whereas a petrol generates less torque so a supercharger is used as this increases the torque throughout the rev range.

In the thread it has been mentioned that we are not comparing like for like when comparing normally aspirated petrols to forced induction diesels. Partially true, however petrols generate higher power due to higher revs and that a forced diesel will still be far more efficient, and use a lot less fuel, than a normally aspirated petrol, let alone a forced induction petrol.

As the fuel burnt is what creates power then we should really look at the power produced per unit of fuel, or thermal efficiency. A diesel always wins here. The best petrols are about 25% efficient, modern diesels are 40-43% efficient with some ship two strokes being better than 50%.

Not surprisingly higher efficiency = lower emissions.

For those with petrol engines try driving without going ever over 4,000 revs. No go.

In a nutshell petrols are fast but thirsty and diesels are torquey and frugal.

Sorry to be so long.

 

[Richard W]

I'm not trying to aggravate, simply trying to balance the debate by suggesting it's horses for courses. Petrol is still king of performance - get some perspective guys. Of course a 320CDI is going to spank a 150BHP Golf GTI - the Golf GTI isn't really a sports car - but try the same trick with an EVO VI or a WRX. Subaru ain't going to fit oil burners to their WRX.... yet.

I quite agree with you - it is horses for courses. My choice is to go the diesel route, it fits with what I need from a car at this point in time. My heart of course is with the 330i - you're quite right what an engine - my point being is that having run a 1.9 turbo diesel (with 150bhp and 330Nm of torque) the 330i (with 231bhp and only 300Nm) has different characteristics to its power delivery and just doesn't 'feel' all that special in comparison (apart from the howl at 6500rpm of course )

Hence the feeling that my choice is the right one for me

 

[steptoe]

Don't forget the long long long engine life of a diesel unit.

 

[Dieselman]

if we cancel forced induction from the equation it means that a 2.3 litre petrol is of similar performance to a 3.2 litre diesel.

QUOTE]

Really? I'd like to see some comparative in gear acceleration figures for cars weighing the same.
Using this formula a CLK 200 K should roughly equate to a 270 Cdi.

Power / Torque
200k = 163 @ 5500 / 240 @ 3500
Cdi = 170 @ 4200 / 400 @ 1800-2600

The Cdi will blow the doors off the 200k due to the extra torque. I bet the 30-50 and 50-70 times are nearly halved in the cdi.
Also remember the Cdi in the E-class is more powerful still.