E90Post
 


MINHS Auto Care Center
 
BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > quick questions for E90Fleet or Stressdoc - why twin turbo?



Reply
 
Thread Tools Search this Thread
      10-09-2006, 03:15 PM   #1
Socom
BMWCCA since '03
United_States
121

 
Drives: 2015 435i
Join Date: May 2005
Location: Atl.


Posts: 5,310
iTrader: (0)

quick questions for E90Fleet or Stressdoc - why twin turbo?

Any idea why BMW went with the twin turbo instead of the sequential turbo in the 335i?
Appreciate 0
      10-09-2006, 03:23 PM   #2
E90Fleet
Major General
South Africa
250

 
Drives: BMW
Join Date: Apr 2005
Location: South Africa


Posts: 8,077
iTrader: (0)

Apparently partly had to do with turbo lag control (535d stilll has some lag) and turbo heat control ( remember the diesel engines that have the sequential setup have a much lower exhaust gas temperature than the petrol engines )

The high exhaust gas temperature is also why hardly any turbo petrol engines have variable vane turbos. Only main one that has it is the new Porsche 911 Turbo, and it uses very advanced, very expesive materials for its turbos.
Most new diesel turbos on the other hand have the variable vane system.


Some say they also didnt want the power too high, else the non-turbo M3 would have problems
__________________
Nominated: Member of the Year, Most Contributing Member


BMW if you are reading, I need a job
Appreciate 0
      10-09-2006, 03:41 PM   #3
poldim
Vroom Vrrooooom
Russian Federation
168

 
poldim's Avatar
 
Drives: 330i
Join Date: Oct 2005
Location: Bay Area, CA


Posts: 3,134
iTrader: (2)

Garage List
2006 330i Sedan  [0.00]
2003 GSX-R 600  [0.00]
Send a message via AIM to poldim
I remember wiki had a little thing on the VGT when I researched about porsches work.

EDIT: found it: http://en.wikipedia.org/wiki/Variabl...y_turbocharger
__________________
-Dmitriy
06' BMW 330i & 03' Suzuki GSX-R600

SG | Beige Dakota | Poplar || iDrive w/MP3 | PP | SP | CWP | PDC | Comfort | Shades || 40% Tint
| Rogue Engineering 12MM Spacers | Black Line Tail Lights
Appreciate 0
      10-09-2006, 03:57 PM   #4
Insider
Captain
13

 
Insider's Avatar
 
Drives: 2007 335i
Join Date: Jul 2006
Location: 4,500 feet above sea level


Posts: 710
iTrader: (0)

Quote:
Originally Posted by Socom
Any idea why BMW went with the twin turbo instead of the sequential turbo in the 335i?
A sequential turbo would have meant one small turbo and one large turbo. The large turbo would produce a lot of boost, and therfore a lot of power. BMW did not want a lot of power. They wanted around 300hp, and this set-up gets them there perfectly.
Appreciate 0
      10-09-2006, 04:00 PM   #5
KL2DC
Moderator
United_States
214

 
KL2DC's Avatar
 
Drives: E90 328i, E85 Z4 3.0i
Join Date: Jan 2006
Location: DC Metro


Posts: 17,753
iTrader: (22)

Garage List
2011 E90 328i  [0.00]
2006 E85 Z4 3.0i  [0.00]
Send a message via MSN to KL2DC
Also...BMW needed to maintain their legendary I-6's feel i.e. linear power delivery/flexibility. I think they put a lot of effort to replicate the feel of a large NA engine with the N54 setup. Great job!!
__________________

Official DC Metro Registry - Current, New & Prospective Area Members Roll Call!
Appreciate 0
      10-09-2006, 06:45 PM   #6
voltron1011
Colonel
86

 
voltron1011's Avatar
 
Drives: 2011 135i, FJR-1300
Join Date: Apr 2005
Location: Wiesbaden


Posts: 2,912
iTrader: (2)

Remember when Dodge had a VNT turbo back in the early '90's? There was very little lag out of the turbo, however the system was total crap with regards to quality, because of what Fleet just explained. I think it was only around for a year or two, before Dodge shit-canned the idea.
Appreciate 0
      11-04-2006, 01:47 PM   #7
2JZfan
New Member
0

 
Drives: Toyota Supra
Join Date: Nov 2006
Location: Midwest


Posts: 7
iTrader: (0)

A sequential turbo system does not necessarily mean that one turbo is larger than the other. The twin turbo Supra is a sequential setup, but both turbos are the same size. At first all exhaust is directed through only one turbo while the other turbo is blocked off. This first turbo therefore spools almost instantly. About the time that this single turbo would run out of airflow to support X psi of boost, the second turbo gets to share in the exhaust and thus it spools too. Of course you also have to block off the intake side of the second turbo during stage 1 because otherwise the boost from turbo #1 would blow backwards through turbo #2 and do you no good. This system is far more complex than a standard "twin turbo setup" and its only real upside is quicker spool. With today's modern turbos, you get X hp with much quicker spool than the turbo that would have been required to make X hp 5 years ago. Therefore, BMW was able to size two twins that would run in parallel and yet still have the desired spool and power characteristics, without all the extra cost and complexity of a sequential system.

And in case anyone is wondering "why twins at all?", two turbos that together can produce X hp will always outspool one single turbo that can produce that same amount of hp if everything else is equal (ie. both turbos have the same caliber of aerodynamics, both are the same type of bearing system, etc.) This is because the majority of the spool time is due to the delay in accelerating the wheels in the turbo, and the moment of inertia of a disc increases polynomially with diameter. In other words, it takes way more energy to accelerate one "big" compressor wheel than it does to accelerate two "small" compressor wheels. BMW seems to put a heavy emphasis on achieving zero lag and this is undoubtedly why they chose twins over a single when obviously there are dozens of single turbo choices that could have supported this power level at a cheaper price point.
Appreciate 0
      11-04-2006, 10:10 PM   #8
stressdoc
Moderator
Dominica
240

 
stressdoc's Avatar
 
Drives: F80 YMB
Join Date: Jun 2005
Location: MO


Posts: 10,159
iTrader: (0)

I bought into the standard line from BMW R&D that small twins provide quick, even spool up. Easier to generate the early and flat power curve that they wanted for the 335. I think there are some interesting new engine management opportunities for turbos with the piezo DI system.
Appreciate 0
      11-16-2006, 03:21 PM   #9
Insider
Captain
13

 
Insider's Avatar
 
Drives: 2007 335i
Join Date: Jul 2006
Location: 4,500 feet above sea level


Posts: 710
iTrader: (0)

Quote:
Originally Posted by 2JZfan
A sequential turbo system does not necessarily mean that one turbo is larger than the other. The twin turbo Supra is a sequential setup, but both turbos are the same size. At first all exhaust is directed through only one turbo while the other turbo is blocked off. This first turbo therefore spools almost instantly. About the time that this single turbo would run out of airflow to support X psi of boost, the second turbo gets to share in the exhaust and thus it spools too. Of course you also have to block off the intake side of the second turbo during stage 1 because otherwise the boost from turbo #1 would blow backwards through turbo #2 and do you no good. This system is far more complex than a standard "twin turbo setup" and its only real upside is quicker spool. With today's modern turbos, you get X hp with much quicker spool than the turbo that would have been required to make X hp 5 years ago. Therefore, BMW was able to size two twins that would run in parallel and yet still have the desired spool and power characteristics, without all the extra cost and complexity of a sequential system.

And in case anyone is wondering "why twins at all?", two turbos that together can produce X hp will always outspool one single turbo that can produce that same amount of hp if everything else is equal (ie. both turbos have the same caliber of aerodynamics, both are the same type of bearing system, etc.) This is because the majority of the spool time is due to the delay in accelerating the wheels in the turbo, and the moment of inertia of a disc increases polynomially with diameter. In other words, it takes way more energy to accelerate one "big" compressor wheel than it does to accelerate two "small" compressor wheels. BMW seems to put a heavy emphasis on achieving zero lag and this is undoubtedly why they chose twins over a single when obviously there are dozens of single turbo choices that could have supported this power level at a cheaper price point.
That's not correct. The Supra Turbo has two different size turbos. A small one, then the bigger one kicks in later on in the RPM band.
Appreciate 0
      11-16-2006, 03:53 PM   #10
txusa03
Major General
284

 
Drives: TS330iPPSP6MT
Join Date: Jul 2005
Location: Planet Earth


Posts: 6,567
iTrader: (2)

there is an article on the new turbo engine in the last bmw magazine (or the 335i brochure) that provides lots of interesting technical discussion and why they did what they did.
__________________
under construction!
Appreciate 0
      11-16-2006, 03:58 PM   #11
2JZfan
New Member
0

 
Drives: Toyota Supra
Join Date: Nov 2006
Location: Midwest


Posts: 7
iTrader: (0)

Quote:
That's not correct. The Supra Turbo has two different size turbos. A small one, then the bigger one kicks in later on in the RPM band.
You are COMPLETELY wrong. I know this car inside and out. Not only do I personally own a Supra, I also own a company that builds custom parts for the MKIV. Both turbos are the same size, this is a fact. I happen to have about 10 take-off units in my shop so I have seen this first hand (not to mention that it's widely documented that the car uses two of the exact same Hitachi turbos). You would think a person would do a simple google before going out of their way to make themselves look like an ass.
Appreciate 0
      11-16-2006, 04:59 PM   #12
Borti
Borti
1

 
Drives: 335i
Join Date: Jul 2005
Location: Oregon


Posts: 115
iTrader: (0)

You cannot have a car with different sized turbo-chargers. It would be putting uneven pressure on the cylinders.
__________________
Quote:
Originally Posted by climkt
fabulous, nothing like a stick shift e92 to add adrenaline and enthusiasm.
Quote:
Originally Posted by aarnt
Drivers over here get their license with MT. Most cars have MT, and all of my friends can drive MT. My chick had an auto once and she sold it in less than a year because she didn't like it. The only replacement to MT for me would be shifters in the steering wheel (ala F1)! Still MT but no clutch.
I don't drink,smoke,eat in my car, ever. And I don't hold the hand of my GF of her thigh or anything else unless there is traffic or stoped in a traffic light. When the car moves, I'm meant to drive it both hands... and god I do it with pleasure

Kudos!
Appreciate 0
      11-16-2006, 06:02 PM   #13
shiv@vishnu
Tuner
United_States
879

 
Drives: X1, 335i
Join Date: Sep 2006
Location: SF Bay, CA


Posts: 17,616
iTrader: (0)

Quote:
Originally Posted by Borti
You cannot have a car with different sized turbo-chargers. It would be putting uneven pressure on the cylinders.
Tell that to Saab who, IIRC, have used asymetical turbo systems on their 6 cylinders before. That means that the turbo was powered by 3 out of the 6 cyliders. Crazy!

-shiv

edited: it was a 6 cyl not a 5 cyl.

Last edited by shiv@vishnu; 11-16-2006 at 10:13 PM.
Appreciate 0
      11-16-2006, 10:00 PM   #14
Last E92 M3
Lieutenant Colonel
25

 
Drives: BMW M3
Join Date: Nov 2006
Location: Virginia


Posts: 1,507
iTrader: (0)

Quote:
Originally Posted by shiv@vishnu
Tell that to Saab who, IIRC, have used asymetical turbo systems on their 5 cylinders before. That means that the turbo was powered by 3 out of the 5 cyliders. Crazy!

-shiv
never NEVER heard of such thing...
hows that work?
Appreciate 0
      11-16-2006, 10:15 PM   #15
shiv@vishnu
Tuner
United_States
879

 
Drives: X1, 335i
Join Date: Sep 2006
Location: SF Bay, CA


Posts: 17,616
iTrader: (0)

Quote:
Originally Posted by Last E92 M3
never NEVER heard of such thing...
hows that work?
It was a v6. The exhaust from the front bank fed a light pressure turbo. The turbo fed the entire engine. It was pretty neat. I suspect it was more for packaging purposes than anything else.

Shiv
Appreciate 0
      11-17-2006, 05:55 PM   #16
Borti
Borti
1

 
Drives: 335i
Join Date: Jul 2005
Location: Oregon


Posts: 115
iTrader: (0)

Quote:
Originally Posted by shiv@vishnu
It was a v6. The exhaust from the front bank fed a light pressure turbo. The turbo fed the entire engine. It was pretty neat. I suspect it was more for packaging purposes than anything else.

Shiv
I am a little confused. Could you elaborate a little further? Were both turbo's applying pressure to the entire engine?

Thanks Shiv.
__________________
Quote:
Originally Posted by climkt
fabulous, nothing like a stick shift e92 to add adrenaline and enthusiasm.
Quote:
Originally Posted by aarnt
Drivers over here get their license with MT. Most cars have MT, and all of my friends can drive MT. My chick had an auto once and she sold it in less than a year because she didn't like it. The only replacement to MT for me would be shifters in the steering wheel (ala F1)! Still MT but no clutch.
I don't drink,smoke,eat in my car, ever. And I don't hold the hand of my GF of her thigh or anything else unless there is traffic or stoped in a traffic light. When the car moves, I'm meant to drive it both hands... and god I do it with pleasure

Kudos!
Appreciate 0
      11-17-2006, 06:55 PM   #17
tommithy
Second Lieutenant
4

 
Drives: 2007 E90 335i
Join Date: Sep 2006
Location: Vancouver, WA


Posts: 286
iTrader: (0)

From what I can tell via google the Saab 9-5 used an asymmetrical turbo design. The used a Garret G17 turbo hooked up to one bank of cylinders on their V6 (which is actually a GM sourced engine) that fed the intake thus turbocharging the engine. The G17 is a very lightweight (by design standards of the day) turbo that didn't take much exhaust to spool up.

The design in general was all about getting low end power and torque in an economical sense. Saab saved money by using a small turbo and got the power they were looking for.
__________________
E90 335i, Sparkling Graphite, Black Dakota leather, Burlwood trim, 6MT, ZSP, ZPP, PDC, Comfort access, heated seats, Navi w/iDrive, Production finished 10/6, Delivered 11/22/06.
Appreciate 0
Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -5. The time now is 09:29 AM.




e90post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST