Carbon Cleaning RS4

[Ginors4]

+3 on vac leak. Especially as it is higher in the rev range (5.5k kick) as this is where most vacuum suction will occur hence more chance of leakage. Yes carbon will pay a small factor. I previously had a vac leak sorted in which the 5.5k kick instantly returned however after carbon clean I only noticed a small difference through entire rev range. In fact it just runs smoother and power delivery feels sharper and less restricted. I would definitely suggest that the vac prob fix was more noticeable after cured.

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+3 on vac leak. Especially as it is higher in the rev range (5.5k kick) as this is where most vacuum suction will occur hence more chance of leakage. Yes carbon will pay a small factor. I previously had a vac leak sorted in which the 5.5k kick instantly returned however after carbon clean I only noticed a small difference through entire rev range. In fact it just runs smoother and power delivery feels sharper and less restricted. I would definitely suggest that the vac prob fix was more noticeable after cured.

There is very little vacuum at high revs - vacuum is generated by the cylinders trying to pull air in against a closed throttle body. The rs4 does have a Venturi system to help compensate but in summary it's the fact that as you apply full throttle and the revs rise there is no or very little vacuum being generated so the amount that is stored will bleed out through any leak.

[Ginors4]

Interesting. The only reason I mentioned this is because on a recent dyno graph my power dipped nearer the end of the rev range, pretty much after 5.5k. This is the point where I thought the vacuum operated the flaps.

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Interesting. The only reason I mentioned this is because on a recent dyno graph my power dipped nearer the end of the rev range, pretty much after 5.5k. This is the point where I thought the vacuum operated the flaps.

More than one set of flaps - the manifold runner flaps are opened at about 3k - 3.5k rpm. The airbox flap is opened at around 5.5k rpm. All actuated by vacuum.
Depending on the vacuum fault it could manifest all differently.
For example, if you are running at a constant 4krpm then the throttle will relatively closed so new vacuum can be produced quicker than a moderate leak (such as a failure of the one way valve under the manifold). Full power/throttle then virtually no new vacuum being generated and you lose some when activating solenoids but if there is a leak then it'll slowly cause things to close.

If you are having power issues over 5.5k then the airbox flap mech is a reasonable place to start. The loss of power isn't so much from the airbox flap opening (which has a debatable amount of impact) but probably more from a faulty airbox flap losing vacuum when activated and causing things like the manifold flaps to slowly close choking off intake air.

It's actually pretty easy to check and diagnose the vac system (just a little fiddly to access the appropriate pipes)