"True" Twin synchronized Turbo system?

[Hurley]

The BMW 335d still has the best turbo setup I've ever encountered. Rather complex, but works awesome. Full boost from 1,500 to 4,500rpm. Small turbo is an itty bitty VGT about the size of the oil fill cap....and at about 2,000rpm it is bypassed completely, and the larger charger takes over. The transition from small to big turbo is all very seamless, and a large powerband is the result.

"Sequential Twin Turbo" - Right? Just like Supra, etc.

 

[98andahalf]

its a kind of sequential, not like a supra. supra uses two turbos of the same size

 

[Smoken Gun]

The BMW 335d still has the best turbo setup I've ever encountered. Rather complex, but works awesome. Full boost from 1,500 to 4,500rpm. Small turbo is an itty bitty VGT about the size of the oil fill cap....and at about 2,000rpm it is bypassed completely, and the larger charger takes over. The transition from small to big turbo is all very seamless, and a large powerband is the result.

Ill back that up. Our 335xi (gasser) has a similiar (if not the same) turbo set-up, that engine pulls HARD from whatever RPM your at, in whatever gear your in until you let up.

A 3.0L Inline-6 gasser than makes 300lb-ft from 1,400RPM and maintains it to 5,000RPM, whats not to like!!

Im itching to get into the 335d!! I want a coupe and manual though....

-Note: The BMW did go through a set-up of turbos already though.

$3,000 for a new set...out of warranty by 10,000 miles... BUT BMW takes care of their customers . They paid for the parts ($3K) and we just picked up the labor.

 

[NickTF]

Cummins head is still too limited in terms of flow, to make use of a low pressure, lots of flow setup like mentioned above, VGT turbo's or otherwise. They still need the air to be rammed down the throat, in order to actually get enough in the cylinder to make use of it.

BINGO BINGO BINGO!!! These heads flow terrible and require insane boost numbers to get the air in them needed to make 700+hp so many of us want.

A question which has been on my mind as of late is would a 475 single by itself make the same power and a 475 under a s362? Assume the 475 uses the same hot side and spool is the same whether compounded or not (which obviously it will not be). My thinking is the compounds come out on top by a good margin everytime given the pressure ratio each turbo will operate in stays much closer to the efficient range of their respective maps vs one turbo trying to generate a pressure ratio of 7+.

 

[dvst8r]

BINGO BINGO BINGO!!! These heads flow terrible and require insane boost numbers to get the air in them needed to make 700+hp so many of us want.

A question which has been on my mind as of late is would a 475 single by itself make the same power and a 475 under a s362? Assume the 475 uses the same hot side and spool is the same whether compounded or not (which obviously it will not be). My thinking is the compounds come out on top by a good margin everytime given the pressure ratio each turbo will operate in stays much closer to the efficient range of their respective maps vs one turbo trying to generate a pressure ratio of 7+.

Problem being is that the over all efficiency of the system is less then that of a single charger, also the heat load being put into the intercooler is a lot greater. My gut feeling is the twins will give you a much broader power band, but the single will still give you more peak power.

EDIT: It is one of the many things I would love to test, but do not yet have the resources to do so. Some day...

 

[NickTF]

Problem being is that the over all efficiency of the system is less then that of a single charger, also the heat load being put into the intercooler is a lot greater. My gut feeling is the twins will give you a much broader power band, but the single will still give you more peak power.

EDIT: It is one of the many things I would love to test, but do not yet have the resources to do so. Some day...

All sounds reasonable.

 

[GRotman]

BINGO BINGO BINGO!!! These heads flow terrible and require insane boost numbers to get the air in them needed to make 700+hp so many of us want.

A question which has been on my mind as of late is would a 475 single by itself make the same power and a 475 under a s362? Assume the 475 uses the same hot side and spool is the same whether compounded or not (which obviously it will not be). My thinking is the compounds come out on top by a good margin everytime given the pressure ratio each turbo will operate in stays much closer to the efficient range of their respective maps vs one turbo trying to generate a pressure ratio of 7+.

A single 475 will make more power than the twins.