Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs

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Jannik07

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	Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « on: June 27, 2023, 03:09:24 PM »

Good evening!

Today I remapped a RS6 with Upgrade turbos. It has also bigger SMIC, upgraded fuel system, 3" Downpipes and bigger Exhaust Manifold.
The car runs great but IMO something is wrong.
At the moment I am using application mode (CWMDAPP = Cool

and control the Wastegate via KFLDRAPP. When I apply 0% WG that setup produces 0.9 - 1.0 Bar of boost. So it has tighter WG-Springs, which is good =)
But with 95% Dutycycle in higher revs it only produces something around 1.2 Bar of boost. Midrange is slightly above sensor limit. What causes the boost to drop that hard in higher revs? In 2.7TT Application Chargers with 0.9 Springs producs easily 2 Bar of boost.

Maybe someone has experiences with these engines =)
I have heard that the intake is a huge limitation. But then i would expect surge or something..

Thanks in advance=)


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Leonhard

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	Re: Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « Reply #1 on: June 27, 2023, 10:45:52 PM »

more details about your "Upgrade Turbos",
are these still K04 based?


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Jannik07

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	Re: Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « Reply #2 on: June 28, 2023, 01:02:27 AM »

The Car is a RS6 so they are K06 based. Its a typical upgrade. bigger compressor that fits in the original housing and reworked turbine.


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aef

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	Re: Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « Reply #3 on: June 28, 2023, 01:45:22 AM »

I am not an export when it comes to rs6 but i had the same on my 1.8t upgrade turbo.
Its not a GTX30 where you will reach 2bar and hold 2bar until redline.

I would suggest to aim for around 1.4bar at first to see if you will have more boost until readline.
Right now you have 1,5+ (above sensor limit) and it will taper down to 1,1bar.
This CAN be normal for this kind of upgrades.
If you aim for 1.4 you will have 1.2bar at nmax, maybe!

Another tip is to play with the cam changeover maps. Do a pull with 22 degree and another one with 0 degree.
Compare airmass and boost on both pulls.

Maybe your 95% is going through the exhaust


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Jannik07

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	Re: Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « Reply #4 on: June 28, 2023, 02:12:10 AM »

thanks for your answer!

I already did play with the cams. If I hold the advanced position longer the boost is higher. But i wont get more maf reading. So its senseless.

I did pulls with different WG from 0% to 95% in 10% steps. Boost is highest on 95%.

I am just wondering because for my RS4 with K06 Turbos and also 0.9 spring I can easily hold 2 bar til redline.


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Leonhard

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	Re: Audi RS6 C5 4.2 Biturbo Upgrade Turbo low Boost @ high revs « Reply #5 on: June 28, 2023, 04:39:57 AM »

don't expect too much from these RS6 turbochargers (part# 53049700028/29) on a 4.2l V8,
in fact they have K04 turbine wheels (50mm inlet diameter) and that's your bottleneck.
Even upgraded with bigger compressor side, limited turbine flow will leed to extensive high exhaust pressure, stop making any valid boost at high revs.
V6 with less displacement ist the better engine concept for these K06/04 chargers.


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