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      09-12-2011, 01:30 PM   #60
U235
Past: 08 Z4MC / 08 M3 / 09 X5 35d
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As everyone has commented, sequential turbos have been done in many configurations, possibly most notably the Supra TT.

However, I think the patent here is on the bypass system. This has a lot of advantages that a regular sequential TT doesn't have. On a regular sequential TT, IIRC the turbos were basically bolted to each other inline, one after another. The varying sizes provided a good combination of low-end torque and high-end power.

For example (smaller turbo on left with wastegate and larger secondary turbo on right):

and

You can see it's basically easy/easier to do this on an inline engine since there's only one exhaust manifold.

This system that BMW is talking about separates the turbos and allows bypass, so the small turbo is used 24/7 (under boost load) and provides great lowend torque and drive-ability to where most drivers probably don't even know it's a turbo. However, when the pedal hits the floor, the presumably larger secondary turbo can provide massive power gains, and as it's sequential it can come on without a sudden rush that makes control an issue.

Furthermore, it provides the ability to use different turbo sizes on a V engine, something that previously wasn't really done. V twin turbos like the 300ZX TT were bi-turbo with equal sized turbos on each exhaust bank.


Here is a TT (biturbo) engine. You can see the independent exhaust manifolds and requirement for two equal turbos.

At the end of the day you have a well balanced engine that can get far greater fuel economy than a traditional sequential turbo.

DISCLAIMER: This is my opinion, I didn't read the article, just the summary and some posts here. I just wanted to clarify the new part of this is the separation and bypass between turbos as well as sequential on a V engine.

Last edited by U235; 09-12-2011 at 01:39 PM..