needforspeed

No worries about disagreeing - I think this an interesting conversation / debate and reflects the sort of discussions I had when I first looked at getting a diesel car

When you talk about downshifting then this gets a lot more complicated.

Up until now we've only talked about the torque produced at the engine, but to get to the wheels it has to go through the transmission. One of the effects of the gears is that they alter the amount of torque available at the wheels (imagine they are 'levers' of differing lengths).

This link gives you an idea of the effect of gearing on the torque output of a chrysler neon in table form. It also explains how this works better than I could:

http://www.allpar.com/eek/hp-vs-torque.html

As I understand it - he is saying that - with the neon (and most other petrols), you are almost always going to get more torque at the wheels in a lower gear (so long as you can maintain speed in that gear below the readline).

SO when you downshift your 530i into 3rd you will have more torque than if you kept it in 4th for the 50-70mph sprint. However, you might start to run out of revs close to 70?

The 530d could also shift down, but likewise might have to change back up again before hitting 70mph (pobably before the petrol due to the low rev range in a diesel)

This all gets super complicated - but I still think that even if you downshift in a 530i - the extra torque in the 530d will make it faster on a 50-70mph run.

On a track where you are going to be trying to constantly stay in the gear that provides the most torque at your given speed. The higher rev range in a petrol car (and peak torque at higher rpms) will mean that it can use more of it's torque at a given time than a diesel - BUT the diesel has more torque to start of with

At the moment petrol still has the edge on the full range - but times are changing - look at this:

Norham - "as for torque HP etc a petrol car will always be faster than a diesel simple fact."

Not this one mate ....

http://europeancarweb.com/news/0603_ec_aud...pe_sebring_win/

Heiss5

needforspeed, thanks for the site, I found it very helpful. Although, as I was reading it, I felt like it backed up my point of view, but then again as you were reading it I'm sure you felt like it backed up your point of view. Thus, the only logical conclusion I could come up with is, we're both right. I think the only way we'll ever truly find out which one accelerates faster is to have a race where anything goes as long as they are both stock cars.

I feel like in his closing arguements, titled "To the Point," he completely backed up my arguement by saying, "A car accelerates hardest with gearing selected to stay as close as possible to the engine *power* peak, subject to the traction capability of the tires." He also said that the power in the previous gear is always going to be higher than the power in your current gear (at least for the neon and near your peak torque and peak horsepower). So, since I know you can go 50 mph in 3rd gear without being close to redline in the 530i, downshifting would give me the best acceleration because I am going to have more power. And although I don't know if this is true or not with a diesel engine, even if you did downshift in a diesel engine the power curve will show that the diesel does not have as much power, and will therefore accelerate slower.

"Shift at the redline, not at the torque peak!"

"Shift to maximize enginer POWER, not engine torque!" which is the same as saying "shift to maximize transmission output torque"

So I guess we just need to race to find out if the 530d's higher torque has what it takes to overcome the 530i's higher power, or vice versa.

2wheels

Heiss5 I've been following your threads with needforspeed and am just about keeping up on the technical stuff. It's fascinating following the theory and I can appreciate both points of view

The reality is that us Europeans have all at one time or another been victim to the VW golf (Rabbit) TDI, embarrassing our highly tuned petrol posemobils. To raise the revs would certainly be "uncool" to put such competition in its place To down shift would be positively embarassing :thumbsdown:

In the early days BMW just watched and listened to the market, unsure whether the diesel engine was the right partner for their sporting saloons, being wedded to the straight six petrol. Today I understand that their diesel engines outsell petrol in several European Markets. Any figures anyone?

This is not just a fuel economy thing It comes down to a bird in the hand being worth two in the bush

Street performance is entirely different than the race track.

BMW has come to the rescue of us battle weary Europeans and provided us with high performance diesel engines

It's simply an added bonus if they are slightly more economical

norham

Norham - "as for torque HP etc a petrol car will always be faster than a diesel simple fact."

Not this one mate ....
Interesting site but this is a one off specially designed and built. I don't for one moment believe this is the future just think of the weight disadvantage for a start in the engines. No sorry I still believe that people who buy diesels do it primarily for economy and resale value with BMW you get a bit of both but thats all, for real economy Audi / VW are way ahead. If you want sheer performance then petrol rules.

pedrollo

This debate will never be resolved in absolute terms.

Is the 530i/530d a fair comparison?
The 530d has a turbo and costs more - and you can take this argument in any direction you want.

You can always 'prove' the point that you are trying to make by picking the appropriate examples.

needforspeed

Agreed the only way to race is to go head to head, but let me explain why I draw a different conclusion to you from the same article.

Peak torque in the 530d is found much lower in the rev range than the 530i. I don't think the shift at the redline statement would be true for a deisel engine, since the power is in the low range.

I also think you will probably be running out of revs above 60mph in 3rd gear and would need to change up to maintain progress.

Anyway - I having driven both 530i and 530d - I chose the 530d for fuel economy AND performance, feeling that, with the auto box as a cruiser (not a racer) the deisel was the faster car.

I'd have no argument that the petrol would win in a 0-100mph drag, or around a track. But in terms of in-gear acceleration I am convinced the deisel is faster.

I have also run both deisel and petrol 3 series and felt that my 320cd (2000cc) was as fast as my 323ci (2500cc).

I think BMW reflected this in the old 3 series line up:

316 (2l Petrol ), 318 (2l Petrol), 320d (2l turbo-diesel), 320 (2.2l petrol), 325 (2.5l petrol) etc....

They clearly equated the 2 litre diesel with the 2.2 litre petrol - which makes sense to me at least having driven the 318 and the 320d which was MUCH quicker on the road.

Don't forget although the petrol engines rev more freely and have a nicer spread of torque the deisels have a turbo !

I think it also fair to say that BMW petrol engines are known for their high levels of torque and that it is a testament to their engineering that the 3.0l petrol and 3.0 deisel are so similarly matched. I think the deisel would convincingly destroy most other equivalent petrol engines on the road.

needforspeed

I would probably have said the same as you a few years ago being a dedicated petrol head. But company car tax forced me down the deisel route with my last car a 320cd (150bhp) and ... I was surprised at it's performance, which was MUCH stronger than my previous 318 (143bhp).

I DO think deisel engines are a legitimate choice in terms of performance as well as economy now, depending on how you want to drive. On the motorway they are a complete joy to drive.

BMW have already done a lot of work on the weight disadvantage, by changing the materials used in construction of the engines.

I think that deisel technology is advancing faster than petrol at the moment and if this continues we will see better performance from deisels (think turbo deisel, common rail, particulate filters, aluminium blocks, bi-turbo's).

Anyway - I think we may have to agree to differ.

pedrollo

...and Audi are starting to race diesels seriously, that should have an affect on the status quo.

needforspeed

And winning ....

Heiss5

I agree, which is why I think a race is in order to see a stock 530i and a stock 530d race from 50-75 mph doing whatever it takes to win (minus running the other person off the track).

2wheels, thank you for your input. Although I'm not really sure if I follow what you're saying. I take it you are more for diesels due to their increase in performance over the last couple years and because they are more fuel efficient. But I'm not really sure what was being debated. You never really said whether you thought the 530d would out perform the 530i or not. Or maybe that's why I was confused, maybe you weren't debating anything, maybe you were just stating that you feel diesels are moving up in the performance world. In which case I agree, and thanks again.

needforspeed, I think we're pretty much on the same page now, these two cars are definitely in the same realm in terms of performance. So as it turns out, the diesel would be a good choice over the gasoline model due to the fact that it is more fuel efficient. As to which one is then more cost effective, well it's a give and take. The diesel costs more to begin with, and diesel itself costs more. But then you're saving due to fuel efficiency. Then with the gasoline engine your saving on initial spending but getting worse mileage. So who knows when those two cost differences will really balance themselves out. 1-3-5 years, I don't know, depends on who's driving and how much. As for the Audi R10 diesel, I don't really want to go into that as I'm sure you never intended anything by it. Obviously diesel cars are making drastic improvements, and sometimes it takes a supercar to really show people that.