Yes, it does cause a restriction. Even on the DOC UK's web site they mention that one of the modifications performed for the free flow exhaust system is the removal of this component. One of the things that I did to my car was I removed all the intake plumbing and ducting. Now I just have a flexable intake hose connected between the filter box and the intake mounted in the pontoon. It does indeed make a differance. While I'm not exactly able to outrun every other car on the road just yet, the engine does appear to breath a bit easier. The throttle does respond a bit quicker, but the imporvement by itself isn't something that I would brag that much about. If you are looking to keep your car stock, or you live/operate your car in a cold climate, you're best to leave the assembly in place. If you're looking for little things you can do to help your car out, this may be one of them. -Robert vin 6585 --- In dmcnews@xxxx, Roland Barmettler <roli@xxxx> wrote: <SNIP> > But isn't this whole air intake system with all its bends, hoses and > that valve posing quite some air flow restriction and therefore some > performance loss ? <SNIP>