Alright, i need a little help here. So I‘m going to give an example so that I can get a remedy to my questions. Thank you for your help! :DSo lets say you have a 1 inch exhaust system all throughout that can let out 10 litres a second (Thats pretty standard, right? I think.), and you‘re using a 1.3l 4 cylinder engine, and you‘re chugging along at 2000 RPM.So to my understanding;2000 RPM / 4 RPM (Ever 4 RPM all 4 cylinders have had one exhaust stroke) 500 RPM / 60 (I need the per second rate) 8.3 RPM x 1.3litres 10.8litres per secondSo clearly this set up has some back pressure equivalent to .8 litres a second since the exhaust can only handle 10 litres per second.Now I KNOW I‘m wrong since I‘m missing a few things; Speed of the gasses, how many RPMs it takes for all 4 cylinders to go throughout an exhaust stroke (I think I‘m wrong), and how to convert litres into psi, and what psi is needed to create a scavenging affect.
Statements: Cylinder capacity is the swept capacity, and can be expressed in liters That is the bore area times the length of the stroke times the number of cylinders All four cylinders exhaust once every two revolutions. (See engine displacement at pedia.) Your 500 RPM divided by 60 is wrong. It is not 500 RPM, but 1000 exhausts per minute. And that number is multiplied by 60 to get exhausts per second, not divided by 60. So, for every 2000 revolutions you get 1000 times four exhausts. Now things get complicated. The total cylinder volume is not 1.3, but 1.3 plus the volume of the head space. The engine needs space for the sparkplug penetration and for valve movement. We do not know at what pressure the exhaust system handles 10 liters per second, nor how much back pressure are willing to have Air comes in at some unknown temperature. It is heated in the cylinder, so when it is released it expands. We do not know the temperature of the exhaust gas. Added to the new volume is the volume of gas generated by the combustion process. There are too many unknown variables to allow us to generate a formula. In engine design, bench testing determines the numbers you are looking for.
