BMW's new twin-turbo Six

[PerfAdv]

Twin-turbo in-line six-cylinderThe all-new Coupé bodyshell clothes the twin-turbo 3.0-litre engine in the new BMW 335i SE that develops 306hp and 400Nm of torque between 1,300 - 5,000rpm. With such performance statistics, the 335i forms the pinnacle of the new 3 Series range.

The 335i SE Coupé accelerates from zero to 62mph in 5.5 seconds, and, if left unchecked, would travel on to an electronically-limited top speed of 155mph. This level of performance is made possible by two turbochargers, each supplying compressed air to three cylinders each. The use of two smaller units ensures that the turbochargers react more quickly to changes in the throttle position all the way to the 7,000rpm red line while also eliminating the previous scourge of turbocharged engines – ‘turbo lag’.

They say here the smaller units react more quickly. Any insight into why they chose to go with the turbos separately feeding 3 cylinders each and not a sequential arrangement. Sequential twin-turbos are supposed to rid of 'turbo lag' and also provide quick reaction at low RPM, with a quick to spool small turbo and offer big power with a larger turbo for high RPM.

Also, equalizing boost from two turbos that independently supply boost to different pistons, how is this managed?

Any explanations, turbo gurus???

[Quiggs]

Originally Posted by PerfAdv

They say here the smaller units react more quickly. Any insight into why they chose to go with the turbos separately feeding 3 cylinders each and not a sequential arrangement. Sequential twin-turbos are supposed to rid of 'turbo lag' and also provide quick reaction at low RPM, with a quick to spool small turbo and offer big power with a larger turbo for high RPM.

Small turbos spool faster. And with a sequential setup, they would have had a significant power spike when the second turbo came in. With the smaller ones, they have a more linear torque band. It's probably set up for better drivability.

Also, equalizing boost from two turbos that independently supply boost to different pistons, how is this managed?

Electronically controlled wastegates.

[PerfAdv]

Originally Posted by Quiggs

... It's probably set up for better drivability.

Meaning with a fat torque curve? I can see this as BMW can easily manage 306 HP with a 3.0 N/A engine. So the turbos are more for torque. This thing is a torque monster with 400 Nm between 1,300 and 5,000 RPM.

[Quiggs]

Originally Posted by PerfAdv

Meaning with a fat torque curve? I can see this as BMW can easily manage 306 HP with a 3.0 N/A engine. So the turbos are more for torque. This thing is a torque monster with 400 Nm between 1,300 and 5,000 RPM.

Yep. BMW probably could build a 3.0 with 300hp, but it'd most likely be a lot more rev happy and a little less friendly in bumper to bumper traffic.

[McReis]

Originally Posted by Quiggs

Yep. BMW probably could build a 3.0 with 300hp, but it'd most likely be a lot more rev happy and a little less friendly in bumper to bumper traffic.

They're aiming for the diesel-torque lovers who wish something a bit more refined. I'd bet as this argument was discussed while making the briefing.

I read that they had the same concern while making the Focus ST. They wanted it to match the diesels in the area where they usually win to any hot-hatch: torque and recoverings.

About PerfAdv question about the big and smaller turbos: I think that is not an issue anymore since the invention of the variable geometry turbos. Am I right?

[bmwpower]

ahh there goes bmw messing up all the fans with the engine numbers again..what happened they used to be such good people...

[Ferrer]

Originally Posted by McReis

About PerfAdv question about the big and smaller turbos: I think that is not an issue anymore since the invention of the variable geometry turbos. Am I right?

The problem is that with the higher temperatures experienced by petrol engines its difficult to make them reliable. Porsche seems to have achieved it, time will tell if it really works.

[henk4]

I wonder about the rationale of this engine, certainly compared to their own twin turbo 530d diesel engine, giving over 270 BHP and and a lot more torque....with a much greater fuel efficiency....

[Quiggs]

Originally Posted by henk4

I wonder about the rationale of this engine, certainly compared to their own twin turbo 530d diesel engine, giving over 270 BHP and and a lot more torque....with a much greater fuel efficiency....

Americans don't buy diesels.

[henk4]

Originally Posted by Quiggs

Americans don't buy diesels.

I was asking for the rationale
Americans are irrational

[magracer]

Originally Posted by henk4

I wonder about the rationale of this engine, certainly compared to their own twin turbo 530d diesel engine, giving over 270 BHP and and a lot more torque....with a much greater fuel efficiency....

I think they are aiming to exploit their (excellent) twin turbo technology in the not-so-diesel-loving USA. Big market there... I think they will do very good with it too.

[Ferrer]

Originally Posted by henk4

I wonder about the rationale of this engine, certainly compared to their own twin turbo 530d diesel engine, giving over 270 BHP and and a lot more torque....with a much greater fuel efficiency....

NVH; noise, vibration and harshness.

[bmwpower]

Originally Posted by henk4

I was asking for the rationale
Americans are irrational

spoken like a european

[2ndclasscitizen]

A sequential system can be quite complicated, this system is much simpler. Its also obvious they aren't going for big power, so a sequential system is irrelevant, is they are designed for big turbo top end, without lag

[McReis]

Originally Posted by Ferrer

NVH; noise, vibration and harshness.

There's not so many of that on them presently. Maybe noise outside is still annoying, but vibration and harshness are gone.