[Insider]

Imagine if BMW used the sequential twin turbo system from the 335D (that's diesel) on the 335I. How much HP would it have with all that boost? 450? 500?

[shimshimhada]

Too much for BMW to be charging only 40K for it.

[mog_pj]

It's nice to imagine though... cheaper to fill up the tank and more horsepower!~

[ward]

it wouldn't work,

diesels run at much lower RPM's

put diesel turbos on the 335 and it'd melt them down in short order

[Gripster]

Plus it would need one heck of a tranny to handle the torque.

[NFS]

Originally Posted by Gripster

Plus it would need one heck of a tranny to handle the torque.

Am I losing the plot here....?

The high levels of torque in the 535d (and the 335d) are characteristics of the diesel engines they use - not the turbo's. You are not going to get that torque from the 335i - cause it's petrol - it will have higher HP though (due to higher rev range) and it will make it's peak torque higher in the revs - which will make it faster.

oh .... and the 335i does use the sequential turbo charging techonology employed in the 535d - which is designed to eliminate turbo lag - almost as big an issue in a petrol turbo as a diesel one.

Simply put - the BMW diesel engines have now pretty much caught up to the petrol ones in terms of on-road performance.

In many cases the diesels will actually pull faster than their petrol counterparts at lower revs, but the petrol will ALWAYS win out when it is in the powerband (high revs). The problem is that on the road it isn't practical to keep a petrol engine in the powerband.

Regardless I have gone for petrol cause I can afford it and it will be more fun (if not faster) than a 330d.

[Insider]

Originally Posted by needforspeed

Am I losing the plot here....?

The high levels of torque in the 535d (and the 335d) are characteristics of the diesel engines they use - not the turbo's. You are not going to get that torque from the 335i - cause it's petrol - it will have higher HP though (due to higher rev range) and it will make it's peak torque higher in the revs - which will make it faster.

oh .... and the 335i does use the sequential turbo charging techonology employed in the 535d - which is designed to eliminate turbo lag - almost as big an issue in a petrol turbo as a diesel one.

Simply put - the BMW diesel engines have now pretty much caught up to the petrol ones in terms of on-road performance.

In many cases the diesels will actually pull faster than their petrol counterparts at lower revs, but the petrol will ALWAYS win out when it is in the powerband (high revs). The problem is that on the road it isn't practical to keep a petrol engine in the powerband.

Regardless I have gone for petrol cause I can afford it and it will be more fun (if not faster) than a 330d.

Actually you are very wrong I will explain why.

The 335i does not use the sequential turbo system that the diesel uses. The 335i has two small turbos working at the same time. the 335 diesel has one small turbo working at first, then a large turbo that comes on later on. It is this high boost turbo that gives the diesel the power. If the gas version had this high boost turbo it would have a lot more torque and power, more than the diesel.

You are wrong about the torque. The 330D and 335D do get their torque from the turbos, without the turbos they would not have nearly the torque. For example, look at the new Mercedes 5.5 liter turbo gas engine. It has 612 torque @1800rpm stock and only 5.5 liters. Compare this to a modern diesel of similar displacement. Such as the 6.0 Ford truck turbo diesel engine which has 570 torque@2000. So you can see the smaller gas engine has more torque at a lower RPM even though it is a smaller engine. Without the turbos these engines would not have nearly the torque. OF course the diesel is much more efficient, but the gas engine can hold the torque for much longer, all the way to 5,000 RPM while the diesel starts to lose torque at 2,500 RPM. That is why the gas engine always has so much more HP, even though torque is about the same providing that they have similar levels of boost from the turbos

[NFS]

Originally Posted by Insider

Actually you are very wrong I will explain why.

The 335i does not use the sequential turbo system that the diesel uses. The 335i has two small turbos working at the same time. the 335 diesel has one small turbo working at first, then a large turbo that comes on later on. It is this high boost turbo that gives the diesel the power. If the gas version had this high boost turbo it would have a lot more torque and power, more than the diesel.

You are wrong about the torque. The 330D and 335D do get their torque from the turbos, without the turbos they would not have nearly the torque. For example, look at the new Mercedes 5.5 liter turbo gas engine. It has 612 torque @1800rpm stock and only 5.5 liters. Compare this to a modern diesel of similar displacement. Such as the 6.0 Ford truck turbo diesel engine which has 570 torque@2000. So you can see the smaller gas engine has more torque at a lower RPM even though it is a smaller engine. Without the turbos these engines would not have nearly the torque. OF course the diesel is much more efficient, but the gas engine can hold the torque for much longer, all the way to 5,000 RPM while the diesel starts to lose torque at 2,500 RPM. That is why the gas engine always has so much more HP, even though torque is about the same

I was losing the plot.

When the 335i was announced the rumours were that it would employ sequential turbos - like the 535d.

You are quite right - it will actual have twin turbos, which I agree is a bit of a shame. To be honest - that's why I didn't believe it.

Presumably the 335d will have the sequential turbo though? In which case it's going to kick the 335i into touch on the road.

Knowing this I now understand and agree

On the second part though - my understanding is that peak torque in diesels IS usually higher than peak torque in petrol engines of the same capacity - even without turbo charging.

Isn't this the reason why ships and lorries have diesel engines? Pulling power and economy where speed is not a deciding factor?

Peak torque in petrol engines is hit high in the rev range and in diesels low in the rev range.

Hence petrol engines always have higher hp than diesel equivalents due to the relationship between hp / torque and revs.

I understood the purpose of the turbos in diesels was mainly to widen the powerband in which peak torque is available (plus provide some boost obviously).

So my 530d wouldn't have peak torque of 500nm without a turbo, but I still believe it would have peak torque in excess of that of a 530i. The problem would be though, that without the turbo, it would only be available for a very limited period and hence the car could not compete in terms of performance.

[Insider]

Originally Posted by needforspeed

I was losing the plot.

When the 335i was announced the rumours were that it would employ sequential turbos - like the 535d.

You are quite right - it will actual have twin turbos, which I agree is a bit of a shame. To be honest - that's why I didn't believe it.

Presumably the 335d will have the sequential turbo though? In which case it's going to kick the 335i into touch on the road.

Knowing this I now understand and agree

On the second part though - my understanding is that peak torque in diesels IS usually higher than peak torque in petrol engines of the same capacity - even without turbo charging.

Isn't this the reason why ships and lorries have diesel engines? Pulling power and economy where speed is not a deciding factor?

Peak torque in petrol engines is hit high in the rev range and in diesels low in the rev range.

Hence petrol engines always have higher hp than diesel equivalents due to the relationship between hp / torque and revs.

I understood the purpose of the turbos in diesels was mainly to widen the powerband in which peak torque is available (plus provide some boost obviously).

So my 530d wouldn't have peak torque of 500nm without a turbo, but I still believe it would have peak torque in excess of that of a 530i. The problem would be though, that without the turbo, it would only be available for a very limited period and hence the car could not compete in terms of performance.

Well I recall some normally aspirated diesels of the past had mostly lower peak torque compared to normally aspirated gas engines of the same size. Of course the diesels peak torque is always down low because that's the only place is can make torque. A gas engine can also be tuned to provide the peak torque down low. But for gas engines in most cases it just makes more sense for the peak torque to be tuned to come in higher in the power band. So that is usually the way they are set up.

[Insider]

For example I found the torque of the 1995 Mercedes 3.0 diesel that was sold without a turbo. It had 134 hp @ 5,000 rpm and 155 lb-ft torque@ 2,600 rpm. So you can see the torque is not nearly as high as a gas engine of the same size. Of course this is from 1995, but I don't think they make diesels anymore without turbos, they would be too slow.

[NFS]

Insider - I think this means we are both right :

http://www.bankspower.com/Tech_somuchtorque.cfm

The turbo boost helps, but so does the low revving nature of a diesel engine and the fuel it burns:

Longer stroke, high compression ratio, higher cylinder pressue all add up to more torque.

I propose a truce

Oh ... and are you sure that mercedes made a diesel that revved to 5000rpm in 1995 ... even the latest engines only rev to around 4500.

[Insider]

Originally Posted by needforspeed

Insider - I think this means we are both right :

http://www.bankspower.com/Tech_somuchtorque.cfm

The turbo boost helps, but so does the low revving nature of a diesel engine and the fuel it burns:

Longer stroke, high compression ratio, higher cylinder pressue all add up to more torque.

I propose a truce

Oh ... and are you sure that mercedes made a diesel that revved to 5000rpm in 1995 ... even the latest engines only rev to around 4500.

Yes good point, good article. Here is the info on the Mercedes from 1995 http://www.mbusa.com/overview/1988/D...AccClassCode=E I remember that engine. It was 24 vavle DOHC normally aspirated diesel. Looks like it had a good power band, just not much peak power.

[NFS]

Originally Posted by Insider

Yes good point, good article. Here is the info on the Mercedes from 1995 http://www.mbusa.com/overview/1988/D...AccClassCode=E I remember that engine. It was 24 vavle DOHC normally aspirated diesel. Looks like it had a good power band, just not much peak power.

I also looked at some e30 statistics on wikipedia - BMW seem to have only made one non-turbo diesel - the 324d and it seems pretty hopeless - 84hp and 152nm of torque. Equivalent petrol models were off the scale in comparison. So my belief that diesel engines were naturally torquey without turbo seems to be bollocks.

So I'm sort of concluding that without a turbo - diesel is hopeless, but with a turbo it will generally deliver more torque than a petrol engine. Which brings me back to where I started in that I still think turbo charging a 335i in the same way as a 535d would not give it the same peak torque as a 535d.

It would be a LOT faster though.

[Insider]

Originally Posted by needforspeed

I also looked at some e30 statistics on wikipedia - BMW seem to have only made one non-turbo diesel - the 324d and it seems pretty hopeless - 84hp and 152nm of torque. Equivalent petrol models were off the scale in comparison. So my belief that diesel engines were naturally torquey without turbo seems to be bollocks.

So I'm sort of concluding that without a turbo - diesel is hopeless, but with a turbo it will generally deliver more torque than a petrol engine. Which brings me back to where I started in that I still think turbo charging a 335i in the same way as a 535d would not give it the same peak torque as a 535d.

It would be a LOT faster though.

True, using a turbo on a diesel does seem to make more sense and provides power more easily. In order to turbo the 335i like the diesel, one would have to strengthen the engine to handle the extra boost which would add to the cost. But if you did the power would be there, but probably not that cost effective. With diesels it is just easier to add a lot of boost to get more power as the diesel engine is built stronger to begin with.

[NFS]

Originally Posted by Insider

True, using a turbo on a diesel does seem to make more sense and provides power more easily. In order to turbo the 335i like the diesel, one would have to strengthen the engine to handle the extra boost which would add to the cost. But if you did the power would be there, but probably not that cost effective. With diesels it is just easier to add a lot of boost to get more power as the diesel engine is built stronger to begin with.

Ok it would be as powerful - but it would probably explode