I tried something. One result is that even without the long tube at the 4/4 to the filter box a good torque at low speeds is achievable. A second result is that the open filter works better at high revs.
The position under the windshield is the best, but it is quite loud at full throttle.
The position to the side of the intake manifold is more tolerable. The car still drives very well but it is warmer and has a low pressure zone. But an air pipe to be added could help in the future.
Since I am overwhelmed from today how well my new gas pedal works I will install the standard air box again out of interest. At least on long journeys the sound of the open air filter annoys me a bit. I have to say that the standard airbox is not as stupidly positioned as you might think. Cold air is scooped up from under the car, even more since I have the bigger Mulfab aluminium radiator.
On the other hand, the air above the engine warms up unnecessarily in the long standard tube.
What I would like to recommend to all people, whatever you do, please reconnect the crankcase ventilation. The engine runs fuller and sounds rounder. The fuel consumption is significantly lower. The Sigma has this inlet in front of the maf sensor, so I did it in this order.
