After having had an eye on the manifold air pressure (map) in the C1, I decided to do some more extensive testing. I had the suspicion that there might be a flow restriction, either before the throttle valve or in the manifold itself. I saw the map on full throttle fall from 100kPa (outside air pressure) to lower then 100kPa.

I wrote a small programm and logged 2 OBD2 PID's as fast as possible. Both RPM and MAP were logged in 4 different runs. As both values are measured during different times, I extrapolated the RPM the MAP was measured. After converting all data, I got the following graph.

So it seems that the engine is having a flow restrition on the intake side and is not producing optimal power. As the throttle valve is pretty big for a 1.0 (58mm if I'm correct) it is either the air intake or the manifold. The intake is one I would not be surprised at. Even for a 1.0, the diameter is pretty small.

2009/09/07 Update

To test if it is a problem with my car or a more generic problem, I did a test with a (much newer) Peugeot 107. It has done just over 2000km, so the airfilter is mucher newer. The graph from this car looks like this.

So it looks like it is a generic problem.

2009/09/08 Update

To see if the problem was with the air intake (before the throttle valve) I did a quick install of a Sparco airfilter on my C1. Then I re-ran the test to see what the MAP valaues would do.

So the problem is gone. All the time the map is at 100 or higher, which is good. The loss which was in the first graph for the same car is now gone. At least for the current engine setup the air intake before the throttle valve is no longer an issue.