silverRS4

Only to realize that in doing so there will be a constant flow of 180 degree air into the airbox if I do so (when the engine is running). There are two other inlets into the box. One from the wheel well and obvious "cold-air" inlet from the front of the car. Does anyone actually know the technical background on this vacuum operated flap? Cold re-starts maybe? It would seem to me that high RPM efficiency has more to do with the intake manifold than it does with letting in a bunch of relatively hot air. Anyway, I sucked the flys out of the air box and closed it back up.

bruised rs4

So you didn't do it?

silverRS4

I'd really like to see or hear some technical background before I do it. I used to build race engines and program ECU's and I know how important it is to keep the air charge as cool as possible. There is a noticeable change in power if the air charge temp increase by 10 degrees, let alone 50. Most late model vehicle air filter boxes have some sort of opening to the engine compartment, but its not there for performance.

Bob W.

the theory is that the flap serves 2 purposes: a) better cold start performance in cold ambient temps, and b) better low rpm performance at high ambient temps. so if those 2 things are more important to you than high rpm performance, leave the flap alone.

personally, I think removing the outer air horn reduces any high ambient temp detriment because it moves the air inlet about 2" away from the aux radiator. my MAF logs seem to support this theory.

ELEVENS

...robbing the engine of needed air. So the current "wisdom" is to remove the offending flap.

bruised rs4

did you see any possible way to route cold air into the flaps intake?

silverRS4

Does it cause a CEL or a fault?

The possibility of the flap not moving freely seems likely after looking at its movement and the clearances involved. This along with the observation that no apparent sensors are monitoring the flap's position leads me to believe that the flap is not critical for high rpm performance. The proper 'fix' to me would be to have some indication that its working as designed, not to just take it out.

silverRS4

Not really - its pretty tight in there

wankeldude

I'm more inclined to do something knowing for sure it has a positive result, rather than doing it because it won't hurt anything.

Bob W.

IIRC, Scott (RI A6) documented a dyno run (or maybe it was a MAF log, I don't remember) where the flap didn't open, and the top end numbers were SIGNIFICANTLY lower than when the flap did open. It's not going to cause a CEL, and it isn't *critical*, but obviously there's going to be a reduction in performance.

Eventually, he set up a switch to manually control the flap position. He no longer has his RS4, but I would ask him about it