another question about cruise control

It's all you get from BMW in their specifications for the car. I'm guessing they have some idea what comes off their production lines and aren't just lying?

While that may be true, the car tested is likely to have been one supplied for performance enhancement - i.e. the owner wasn't happy with what he had for some reason.

You're not seeing the context of what I'm saying. The first few letters "I'm" might just link to the car "I" drive. This is a 3 litre

Admittedly, there are more manual 325d (which is why I have one) than

Perhaps this is why driving a modern car like it's an old fashioned car "makes no sense" to you then?

I too am a mature driver and was brought up in the old ways when most cars were a bit rubbish. Embarrassingly, it was a retired gent who told me my driving technique was out of date and would benefit from improvement. That shocked me into re-learning to drive properly. The knock-on is that my driving technique now makes complete sense where it didn't before.

On a common rail diesel, an ecu sits between the "idiot" and the engine. The ecu is programmed to provide up to whatever maximum the manufacturer deems reasonable for the components.

The engine isn't delivering any more torque, so doesn't need any alteration. You can already make it pull hard from very low revs in a high gear if you wish.

Not quite sure why you think there is more stress on the mechanics at low revs rather than high?

Peak torque on a blown engine isn't the same as on a NA one. It is a function of how hard the blower is working.

If you dig deep enough in the archives, you find a bit more.

Here is a list of M57 engines and their outputs:

Engine code; Power; Torque@rpm; Year

M57D25; 163 PS (120 kW; 161 hp)@4000; 350 N·m (260 lb·ft)@2000-2500; 2000

M57TUD25; 177 PS (130 kW; 175 hp)@4000; 400 N·m (300 lb·ft)@2000-2750; 2004

M57D30; 184 PS (135 kW; 181 hp)@4000; 390 N·m (290 lb·ft)@1750-3200; 1998

M57TUD30; 204 PS (150 kW; 201 hp)@4000; 410 N·m (300 lb·ft)@1500-3250;

^ I believe this one is from your car^

M57TU2D30; 231 PS (170 kW; 228 hp)@4000; 500 N·m (370 lb·ft)@2000-2750;

As you can see, these engines that have the same origins as yours, all have a range of rpm where the peak torque will occur. It does mean not that the peak is from X rpm to Y rpm.

Some people always want more than they already have.

The other chart from Hartge.de helps to demonstrate that similar engines do not perform exactly the same as eachother. That engine had a peak torque at just over 2,000 rpm, hence that the peak torque will occur somewhere in the range of rpm quoted.

David

Not in the context of the sentence, no.

Fascinating.

The effect would be magnified by having a taller gear.

This is a basic effect of gearing and the reason people use levers, gears and pulleys. Just try setting off in top gear then tell me the engine isn't a bit more stressed than if you set off in first.

Sorry, I know what you're saying, just not how it relates to this discussion of putting a bigger gear in my turbo car because I don't have to change down on the motorway.

I don't think my 197PS engine is in that list. However, it is likely just to be a mapping difference away from one of the ones above.

Agreed.

I never claimed differently. I just repeated what the BMW spec was as a reason for the lack of a need to change down out of top on the motorway to maintain speed.

I used to have an Alfa..I know all about factory output tolerances on a grand scale! ;-)

Well that's what happens when you extract one sentence and disregard the paragraph. Are you a tabloid journalist by any chance?

The 'stress' would be on the clutch, not the engine.

Fair enough, I knew it was short of one or two entries, but it was just an example of the torque ranges of some of the M57 family.

Absolutely, mine never has either.

It is not surprising that petrol engines with a lot of torque still need to change down because they are not usually cruising at the revs near maximum torque in top gear.

:-)

David

What do you mean by "stress"? As in Young's modulus terms or do you have something else in mind?

Why is your "stress" any greater than just driving along normally and using maximum torque?

Well both, more torque is more stress, it's in the definition, torque =forcex distance, stress =force/area.

But the engine doesn't develop maximum torque at such low revs. You'd need a steam or electric motor for that.

No it's what happens when someone can't express themselves in English.

Are you poorly educated by any chance?

No, but if you halve the rpm you'll double the required torque to maintain the same speed or accelerate at the same rate.