Heiss5

Good call, I didn't notice that, my bad. But I'm still getting pretty good either way, or they're getting pretty bad. So the question remains, are the diesels even worth it?

pedrollo

Sorry to poop the party boys but US gallons are SMALLER so Heiss is actually doing even better!

Is diesel worth it? WIld horses wouldn't get me back in a petrol after having a 535d.

Heiss5

Why not?

needforspeed

Good god.. your right ! Teach me to do sums this late.

1.2 us gallons = 1 uk gallon

So Heiss is getting up to 36*1.2 = 43.2 (uk) mpg - amazing in a 530i

I think this just shows what a factor speed limits and road conditions are.

What I do know if that - on average I am getting about 32 (uk) mpg from my 530d and would expect this to be more like 26 mpg in a petrol model. Given our petrol costs that is enough to matter.

The 530d was more expensive though and I don't pay co car tax, so the financial argument isn't that big a deal. What does matter though is available torque and .. for the sort of driving I do there is more of this (500nm) in the diesel. So when I am in the peak powerband (2000-3000 rpm or 50-70mph) the diesel is able to accelerate almost as fast as a 550i - which is a big deal on british roads.

Apologies to Heiss for my backward sums.

Heiss5

No harm done, so no worries.

2wheels

Should you compare 530 petrol to 530d

If torque and real life low down power are taken in to consideration then the 525d would probably be a fairer comparison In this case the diesel purchase price, fuel consumption and depreciation would all be lower

Large, heavy cars = diesel small sports pocket rocket = high strung petrol

Heiss5

I know I'm not the best guy to come to for engine knowledge/comparisons, but I feel like I know a little, and I'm slightly confused as to why people think that diesel engines give you better acceleration? I know they have more torque which gives you that "kick in the pants" feeling. But, diesel engines produce low end torque, typically used for hauling/towing.

Yes, diesel engines hit their peak torque a lot sooner than gas engines. So if you were to just hit the gas in the gear you were in, then yes a diesel engine might take off a little faster, but if you're really trying to go, especially at freeway speeds, that's not what you would do at all. You would downshift, raise your RPMs and thus get closer to peak horsepower, and peak horsepower means more acceleration. Diesel engines don't run at higher RPMs like gas engines do, and typically, higher RPMs means more horsepower and therefore more acceleration.

So, 0-60 mph, yes a diesel engine might get a slight jump on you in the beginning, but in the end the 530d is doing 0-60 in 6.8 seconds while the 530i is doing 0-60 in 6.5 seconds.

So where I'm I getting this confused? Or is no one saying that the diesels are faster and I'm just retarded?

needforspeed

I think the following is correct, but if not - I am sure someone will correct me.

Torque is the twisting force that makes the car accelerate. HP is more esoteric and is a representation of the 'work done' by the torque at a given rpm.

In terms of acceleration - forget horsepower - think torque.

People often talk just about peak torque, which is not the whole story, what matters is the torque curve and the cars gearing (ie how much torque is available through the rev range and how the gears ratios are set up to enjoy this).

In most petrol cars, torque increases gradually and usually peaks near the rev limit. In diesel's you tend to get a lump of peak torque at low revs, which quickly decreases as the revs increase.

The peak torque (500nm) in the 530d is as high as a big V8, so although it isn't there for long, when you can use it the car accelerates VERY well.

Fortunately, the gearing means that this torque is pretty useable - so typically I'll be cruising at 50mph at somewhere round 2000 rpm - with peak torque available so 50-70 is VERY fast, with a 6 speed box, the torque is well spread through a range of speeds.

So in a well set up diesel (like the BMW ones) on a road the levels of AVAILABLE torque are typically higher than in the equivalent petrol model.

SO although the petrol MIGHT beat the diesel round a track (where it can be kept at very high revs) or in a drag race (where it can get off the line faster) on a road the diesel will often accelerate faster.

Incidentally the sequential turbo technology in the 535d is designed to smooth out the torque, letting the higher levels arrive sooner and more gradually, by providing a small boost at low revs followed by a great big one once you get going. This is why the 0-60 time in the 535 is so good and why it can punch with the 550i

As I said - if I have anything wrong please jump in - but I think this is how it works.

KAF

The 0-60 acceleration time is academic, it is no indication of how you drive your car.

The acceleration you really use in a car is in the range 40-70 mph for overtaking, that is when you really need instant response. This is where the diesel excels for the reasons needforspeed has explained. You get the blast of power without the need to go through the gears.

Whilst they may not have to out and out acceleration times of a petrol engine, diesels are very driver useful in the real driving world.

525dse

HP is the speed that the wheel turns, Torque is the force the wheels turn. More Torque gives your engine and and you a easier drive e.g. when pulling away you need alot of force to push the car from the start. However as speeds increase HP is more important. I think this is how it works....