The exhaust system represents Phase 2 of my Peugeot 407 upgrade. It consist of a 4-2-1 extractor, a mid and rear muffler, all had to be customized from scratch because there was none off-the-shelf in the local automobile industry yet something I wanted badly having lived my driving life with modified cars. The 4-2-1 rather than 4-1 version was preferred for torque rather than power. The improved release of the exhaust gas then showed weakness in the stock rear muffler with irritating resonance between 1,500-2,500 rpm. A custom rear muffler was built but the rear space was inadequate to quiet the exhaust as close to the stock so a fairly large mid muffler had to be built. All these modification will definitely auto-calibrate the oxygen reading in the exhaust which usually will require a full petrol's tank consumption of which at the point of writing this article, I have not even used up 3/8 of the tank. However, driving the car in style as I usually do in town, I find that I am getting better and better fuel consumption because I usually do 2 return trips to Kuala Lumpur and back in 1/8 tank but can now do 3 return trips. All this means I should get even better mileage if I were to use the car outstation. Well, still too early to get consistent results!