RI A6

Are you feeling more power at the top end now? Or at least are you feeling it more consistently?

I've discovered that the intake butterfly does not always open at 5000 rpm. I now believe that the ECU also uses a temperature check, and if the temperature is too high the valve is never opened. This would go a long way towards explaining dyno differences and low HP readings.

I'm doing some research on this right now.

sparkhill

Very interesting idea <tracks thread>

daveak05

you and I talked about that butterfly being temp controlled, or not, awhile back, remember? i figured it had to be either temp or vacuum or both. the ECU has to act on some input, some criteria in order to open and close the valve, and RPM alone never sounded right, to me.

yanking it completely out, i have to wonder of that will have some effect on cold operation or low end drivability, even if minor. your thboughts?

RI A6

I'm trying to run some tests to see if I can monitor it's behavior. I'm pretty convinced that it's cutting top end power in many cases. It can't be vacuum controlled, since they use a vacuum accumulator in this engine. Now I'm thinking that it uses temperature as one of it's controls, or some other set of obscure input conditions.

daveak05

but, there's a vacuum line to it, right? that is the actuator, but the vacuum pressure may also tie into when it opens and how much too.

my view is that if it "typically" opens fully above 5000 rpm, as earlier claimed, then it acts to lean out mixture and/or add air flow. what it's doing at other rpm levels and particulary during cold engine operation would be something to consider. it could also act to enrich fuel mixture by reducing air during warm up.

also there could be electronics that open and close the vacuum supply to it. i have seen this on even comparatively primitive engines of earlier design(past cars of mine...the 88 Conquest TSi for one).

in any event, removing it completely could have implications.

ELEVENS

I can't really say if it's faster or not. But with the flap removed, the intake "music" when opening the throttle (at any RPM) is worth it to me. It has really lessened my desire for an aftermarket exhaust.

Looking forward to your research into the deep dark secrets of the ECU(s)...

RI A6

It uses an ecu controlled vacuum actuator. If I am monitoring the correct Vag-Com group, then it did not open during my test yesterday.

097,0,Intake Air Change-Over
097,1,Engine Speed,(G28)
097,2,Engine Load
097,3,Coolant,Temperature (G69),Range: -40.5...+135.0 °C\nSpecification (Warm): 80.0...115.0 °C
097,4,Status,Intake Air Flap,Display Range: ON/OFF

VerrÜckt

<center><img src="http://pictureposter.audiworld.com/52044/b5_rs4_intake_flap.jpg"></center><p>and the opening/closing is controlled by a two variable function of RPM and massflow (load). It also operates only when vehicle speed is over 50 km/h.

Now it does get more complicated as massflow is greatly effected by air temperature and intake air temps, so any efforts to accurately estimate how the system is working my be difficult.

I'd be very surprised if the B7 system was significantly different, but you never know.

daveak05

it looks as if there is more to it than simply engine speed. the info and comments by Chris above may hold the answer.

RI A6

I assume that some owners removed their flaps. Are you aware of the results, either on the dyno, or in drivability. It seems to me that the main reason for the flap is to meet European noise standards.

I'm assuming that measure group 97 (Intake Air Change-over) reports status on the intake flap. If that is the case, then I did not see the flap ever open in my VAG tests. I think operation of this flap may hold the key to missing power felt and measured on the dyno. When the flap does open, you can definitely feel and hear it.

According to the service training manual the flap operates like this:

To ensure a sufficient supply of air to the engine at high RPM, the power flap in the air filter is opened at engine speeds higher than 5000 RPM and at road speeds higher than 200 kph.

The power flap is opened and closed by a vacuum actuator which is map-controlled by the ECM via the Intake Air Switch-Over Valve N335.


It seems to me that they left out the part about temperature or mass air-flow.