# biturbo I-5 - is it possible?



## Entwerfer des Audis (Jun 16, 2006)

I've discussed this briefly before, but just thinking... are biturbo motors a turbo for some of the cylinders, or do they have one small turbo for low-end torque and then disconnect it at high rpm and revert to a big turbo for top-end power? 
If each turbo only works on some of the cylinders, an I-5TT wouldn't work because you'd have to stagger boost, which would generate different torque curves for two sets of cylinders, whereas if you had the same boost, it would be distributed over more cylinders and the boost would be spread thinner for the turbo working more cylinders (in this case, 3), and thicker for the turbo working fewer cylinders (in this case, 2). 
Could Audi do this for the current I-5 that's in the Jetta and use it for the RS5 or TT-RS? Let's hear some feedback!


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## eurowner (Jan 26, 2002)

If you have the time, money and fabrication skills, please take good pictures and detailed instructions!


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## Sepp (Dec 10, 2002)

*Re: (eurowner)*

Tough to say. Anythings possible, but not cheap = no one will mass produce it.
The twin turbo 6 in the B5 S4 has twin turbos, and each turbo is feeding the inlets for the set of 3 cylinders on each respective head.
(same size compressor)
VW is already doing something simular with a supercharger for the low end, the supercharger disengaes and a turbo takes over for the top end.
One thing with the 5 cyilinder is that it takes up a bit of room. With the older Audi's, it can be tight enough with just one turbo. One would have to design a longer hood to fit all that goodness in. (IE Supra)


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## Entwerfer des Audis (Jun 16, 2006)

*Re: (Sepp)*

Hmmm... 
Possible to mount turbos somewhere else? I remember some Henessey Viper had a turbo mounted under the engine. Or maybe under the trunk or back seat? 
I don't at all have the means to do this (not even an I5, or any car, for that matter), but I just think it would be interesting. 
Do you foresee a twincharged I-5 in the TT RS or RS5?


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## WAUOla (Apr 15, 2005)

*Re: biturbo I-5 - is it possible? (Entwerfer des Audis)*

There once were one of these discussions on another forum PerL & I are using.
First of all, i think the definitions came to this:
singel turbo - need no explaination
twin turbo - dual setup of identical turbos, like the Audi 2.7T etc
biturbo - setup of two turbos, to better gain wanted preferences
i.e. one small and one big to give good response from bottom to top revs
(due spoolup vs delivery and so on...).

Now: over to the "important" thing. Yes you can do a bi/twin setup on the
I5s. Actually, 4km from where I'm writing this, there is an original 20Ved
quattro that was prepped with the internals for a 550hp 2.2L setup
(achieved by singelturbo in another S2 coupe at the same firm) and it
features 2x K04 from 20V cars.
Ideally you'd get better spoolup from two smaller turbos than one big,
but getting pulses from 5 cylinders into two turbos wasn't that good, so
new turbotechnology should get you there as well up until 600hp.
Might consider charger and a big turbo..?


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## Entwerfer des Audis (Jun 16, 2006)

*Re: biturbo I-5 - is it possible? (WAUOla)*

Wait, so biturbo≠twin turbo?


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## WAUOla (Apr 15, 2005)

I guess that is a case of definition...
twin turbo = 2x equal turbos
bi turbo = use of two turbos, i.e. one big and one small


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## 84cgtturbo (Apr 3, 2003)

*Re: biturbo I-5 - is it possible? (Entwerfer des Audis)*

Apparently Audi toyed with the idea back in the day (at least on one of their race cars) -


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## WAUOla (Apr 15, 2005)

We discussed that pic earlier this year.
Dual K24 setup. Most special is the 25V engine though...


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## WAUOla (Apr 15, 2005)

Take a look at this setup (found in Dope Shizzz of Golf mk1 forum).


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## asynchron (Mar 30, 2003)

*Re: (WAUOla)*


_Quote, originally posted by *WAUOla* »_bi turbo = use of two turbos, i.e. one big and one small

If I'm not mistaken, this is also what's typically referred to as a sequential turbo setup, as in the 959. the larger one only becomes active at high revs, so as not to apply its drag to the motor at low revs.


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## Entwerfer des Audis (Jun 16, 2006)

*Re: (asynchron)*


_Quote, originally posted by *asynchron* »_
If I'm not mistaken, this is also what's typically referred to as a sequential turbo setup, as in the 959. the larger one only becomes active at high revs, so as not to apply its drag to the motor at low revs.

That makes sense, but answer me this - why would you have two turbos of the same size, both active at all revs, instead of a single large one or a sequential setup?


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## needa4kq (Feb 15, 2007)

*Re: (Entwerfer des Audis)*

So, if you look into it Audi refers to the 2.7t as a bi-turbo, using two of the same size turbos one on each cylinder bank of a v-6. Toyota, on the later Supra Turbos with one small and one large turbo with an actuator to switch between them based on RPMs/exhaust volume, is considered a twin turbo.


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## WAUOla (Apr 15, 2005)

I DON'T think you HAVE TO say one thing or another, some does, some doesn't.
I'll try to get a pic of that urquattro biturbo.


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## firstpost (Oct 14, 2007)

*Re: (WAUOla)*

In reference to the post above........
The larger turbo never produces drag on the engine. Its always there, interupting the exhaust flow at all times. The smaller turbo provides lower RPM power and feeds the larger turbo for more boost throughout the Tach's range.
Or maybe I'm wrong.


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## WAUOla (Apr 15, 2005)

I just found this on a S2 forum. Haven't heard any more from owner of the one in this city.
But, I can't say if it is this engine or not, as they had such a green S2 coupe before, and might just have testmounted the engine in it.


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## 71DubBugBug (Dec 3, 2006)

that would be a nightmare, especially to tune


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## Schecky (Sep 23, 2007)

*Re: (71DubBugBug)*


_Quote, originally posted by *71DubBugBug* »_that would be a nightmare, especially to tune 
oh yea, i can only imagine what a pain it would be, even just trying to run software for that would be ridiculous, everything would have to be done from the ground up


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## WAUOla (Apr 15, 2005)

Why would it be a nightmare to tune?








It's only a matter of adjusting the map...
Only problem I can see is doing a parallell, due
bad pulsing (and I think that is what this car had).
Doing a staged setup properly should be sweet.
Going K04 into K27 for instance...


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