# sequential bi-turbos



## GTTechnics (Apr 2, 2003)

Over the years, I have heard of cars with two turbo's, one bigger than the other. I have heard of them called sequential turbos. Now, I know the logic would be to have a small turbo to spool up the big turbo, but I have never actually seen anyone use this setup. What really doesn't make sense to me is the layout of the exhaust manifold. Would it be like a twin turbo setup in which 3 cylinders exhaust into one and 3 in the other (assuming we're working with a six)? I would think the difference in backpressure would cause an imbalance on the engine. The other alternative- one turbo's downpipe going into the inlet of the other turbo seems ludicrous. Is this a myth? HAs this been applied on any factory cars?


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## TBT-Syncro (Apr 28, 2001)

*Re: sequential bi-turbos (GTTechnics)*

toyota supra would be the most common car that had a seq setup. But every big power supra is a single turbo conversion.


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## MarcoVR6SC (May 3, 2003)

*Re: sequential bi-turbos (GTTechnics)*

It is done like this:
























But it is the biggest compressor (first stage) that 'spools up' the smalest compressor (second stage).

_Modified by MarcoVR6SC at 8:16 PM 5-5-2004_


_Modified by MarcoVR6SC at 8:23 PM 5-5-2004_


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## GTTechnics (Apr 2, 2003)

*Re: sequential bi-turbos (MarcoVR6SC)*

IS anyhting dubbed a Biturbo set up like this? Someone said that the s4 is like this, is that true?


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## MarcoVR6SC (May 3, 2003)

*Re: sequential bi-turbos (GTTechnics)*

No, the s4 biturbo 2.7l has the turbo's in parallel.


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## GTTechnics (Apr 2, 2003)

*Re: sequential bi-turbos (MarcoVR6SC)*

Thank you...I thought running a k03 into a k03 sounded fishy


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## MunKyBoy (Sep 16, 2002)

*Re: sequential bi-turbos (GTTechnics)*

i thought that S4's ran the k04's??


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## 98a4 (Sep 17, 2003)

*Re: sequential bi-turbos (MunKyBoy)*

Nopes ko3s...rs4s run ko4's


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## MunKyBoy (Sep 16, 2002)

*Re: sequential bi-turbos (98a4)*

ahhh, 10-4! Learn something new every day http://****************.com/smile/emthup.gif


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## peteM3 (Sep 10, 2001)

that turbo setup that was posted isn't what you would run on gasoline. That setup would be if you wanted way over 50psi of boost for a fuel motor or diesel or something. 
normally a gasoline motor the 1st compressor never feeds the 2nd one. 
Turbos operate on pressure *ratios* so if both are operating independantly at 3:1 PR you end up with 3x atmospheric or just under 30 psi. Link them togheter 1st into second one like that and the 1st turbo at 3:1 generates 30 psi, the second generates 3:1 with 30 as the beginning PR = like 90 psi.


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## GTTechnics (Apr 2, 2003)

*Re: (peteM3)*

So how would the stock supra TT be different then?


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## BubonicCorrado (Jul 24, 2003)

*Re: (GTTechnics)*


_Quote, originally posted by *GTTechnics* »_So how would the stock supra TT be different then?

supra runs one right into the other...
as does the RX7...


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## peteM3 (Sep 10, 2001)

*Re: (BubonicCorrado)*

i'm willing to bet they only run the exhaust portion straight into the other. Given the low stock boost of those cars theres absolutely no reason for sequential compression, nor would it work very well. but, stranger things have happened so i'll ask my rotor head buddy later. i think he even still has his stock setup in a scrap heap somewhere lol.


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## MarcoVR6SC (May 3, 2003)

*Re: (peteM3)*


_Quote, originally posted by *peteM3* »_that turbo setup that was posted isn't what you would run on gasoline. That setup would be if you wanted way over 50psi of boost for a fuel motor or diesel or something. 
normally a gasoline motor the 1st compressor never feeds the 2nd one. 
Turbos operate on pressure *ratios* so if both are operating independantly at 3:1 PR you end up with 3x atmospheric or just under 30 psi. Link them togheter 1st into second one like that and the 1st turbo at 3:1 generates 30 psi, the second generates 3:1 with 30 as the beginning PR = like 90 psi. 

Thats not really how it works, you can see in detail how it works on this site : http://www.turbos.bwauto.com/en/products/t_r2s.asp
Just a portion from the site on how it works: 
The regulated 2-stage turbocharger consists of two turbochargers of different sizes connected in series that utilize bypass regulation. The exhaust mass flow coming from the cylinder flows into the exhaust manifold first. Here it is possible to expand the entire exhaust mass flow using the high pressure turbine (HP) or to redirect some of the mass flow through a bypass to the low pressure turbine (LP). The entire exhaust mass flow is then utilized again by the low pressure turbine (LP).








The entire fresh air flow is first compressed by the low pressure stage. In the high pressure stage, it is compressed further and then the charging air is cooled. Due to the precompression process, the relatively small HP compressor can reach a high pressure level so that it can force the required amount of air to flow through the system.
At low engine speeds, i.e. when the exhaust mass flow rate is low, the bypass remains completely closed and the entire exhaust mass flow is expanded by the HP turbine. This results in a very quick and high boost pressure rise. As the engine speed increases, the job of expansion is continuously shifted to the LP turbine by increasing the cross-sectional area of the bypass accordingly.
Regulated two-stage turbocharging therefore allows for continuous adaptation on the turbine and compressor sides to the actual requirements of the operating engine.
The system can be regulated via pneumatic actuators that control the bypass valve in the same manner as when used in mass-produced turbochargers with swing valves. This makes it possible to model a compact charging system (when detailed knowledge of the complex system response is available) that fulfills the highest torque, response and power requirements while utilizing proven components.



_Modified by MarcoVR6SC at 2:27 PM 5-6-2004_


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## peteM3 (Sep 10, 2001)

all i was saying is that setups like that are generally for high boost applciations not 91 octane crappy pump fuel. I suppose you could size them both to have like 1.5 PR's lol and work on pump fuel but what would be the point other then to build something complictated. 
also the system that was shown in the pictures, that i was speaking of... has no bypasses of any sort. Its straight from one turbo to the next on both exhaust and intake sides.


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## MarcoVR6SC (May 3, 2003)

*Re: (MarcoVR6SC)*

So actually it's done for achieving max torque true the hole range of rpm's, just like a VNT should do, but then for petrol engine's.


_Modified by MarcoVR6SC at 2:47 PM 5-6-2004_


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## MarcoVR6SC (May 3, 2003)

*Re: (MarcoVR6SC)*

You can not see the bybass, it's integrated in the first turbine housing, well somewhere below in the picture.


_Modified by MarcoVR6SC at 2:42 PM 5-6-2004_


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## peteM3 (Sep 10, 2001)

well, if there is a bypass present, you can't see it lol or any related plumbing. 
In either case there definantly is no compressor bypass. but i think like you say that might be unneccessary you could use the first compressor just to lower the PR of the second. 
I just don't see it being feasable for a DIY'er anytime soon. it certainly would be a neat project. 
I"d say if you just want a fat powerband just go with a GT-xxR ball bearing and a nice manifold. 
the real key to getting that to work would be controlling the bypass valve! you'd have to keep the 2nd turbos rpms down in the top end or your pressures would skyrocket. Thats when you need a buddyy who's an EE to make you some electronic ****. 


_Modified by peteM3 at 2:56 PM 5-6-2004_


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