I have noticed that my Morgans with spare wheel have less exhaust fumes in the interior than such Sport models or the P4SS. Maybe a good part is sucked into the spare wheel opening. One effective measure is to open the side windows. This will significantly reduce the negative pressure in the passenger compartment and less exhaust gases will be sucked in.
Another point, when the ECU is reprogrammed there are two areas. If the full load range got a smaller lambda, then the engine runs richer, you could smell it and it doesn't change. If the ECU has been changed in the part-load range, it may be that it learns and that the exhaust gases become less smelly after about 400 km. This was the case with my Elise after reprogramming.
