I found this article on F1 exhaust systems and I think that it is very interesting especially for those technical F1 fans discussing this subject in another forum named “Exhaust opening” .
‘The moment the outlet valves open, all hell is let loose. One of the 10 cylinders in an f1 engine has just inhaled 300cc of air, laced it with a jet of fuel, compressed the mixture to 10x atmospheric pressure and flung in a spark. At 900 degrees Celsius the gasses produced when the mixture explodes whip past the titanium outlet valves and into the exhaust system at the speed of sound. But far from being a simple means of evacuating hot, high-speed gases, modern exhaust systems have a crucial part to play in determining the power and performance of a racing engine.
Compared with the exhaust of a road-going car, the short but serpentine system in a formula racer looks pretty simple. Each bank of cylinders features a number of artistically twisted steel tubes, with no catalytic converter and no silencer to hinder the flow of the exhaust gases and prevent the engine breathing freely. And yet designing a F1 exhaust system is an extremely complex business that calls for an intimate knowledge of the laws of acoustics if the engineers are to tease the last reserves of power out of the engine. That’s because, like in a trumpet, the exhaust gases vibrate at a specific frequency depending on the speed of the engine. As the valves open and close, they generate a pulsating column of exhaust, with regular peaks and troughs of pressure. To ensure that the 5 cylinders per bank don’t interfere with one another in this respect, all the exhaust pipes must be the same length. And at the end of the collector, the exhaust gasses from each bank exit the car from a single tailpipe.
Racing engines bred for maximum power work with a high degree of valve overlap. That is to say, the inlet valves are opened before the piston reaches top dead center (TDC) while the outlet valves are still open. At this instant, a perfectly tuned exhaust system will ensure that there is already under pressure in the combustion chamber, drawing in the mixture for the next charge. So the induction stroke which is generally triggered by the downward motion of the piston is in this case initiated by the exhaust system . Thus the intake and exhaust system together form an integrated and highly sensitive gas vibration system which influences both maximum power and torque.
At peak revs, a formula engine will blast out exhaust gases 95,000 times a minute. To scavenge maximum power the exhaust pipes need to be as short as possible. Unfortunately , to help generate maximum torque and responsiveness at lower revs, longer splender pipes are called for. As F1 regulations don’t permit variable-geometry exhausts, the answer lies in the best possible compromise.
The current preference for tailpipes that emerge upwards through the rear trim at either side of the car has made life easier for exhaust designers.
Nevertheless, F1 exhausts rarely completes more than 1200km since the need to save weight means they have to be designed close to the limit. The thickness of the heat-resistant steel adopted from the aerospace industry varies but is never more than 1 millimeter. But when eventually kills these waste-gas works of art is not vibration or temperatures of 1000 degrees and more, but stress, The different radii of the various pipes ultimately produce fatigue which leads to cracks where the stress is greatest. Not surprisingly, at this high level of performance even the best exhaust are soon exhausted !!’