01-05-2020, 09:02 AM
Some may be wondering what all this is about.
Individual pipes are to harness momentum effects and pressure pulse reflections. Because adjacent cylinders fire just half a rev successively, and valves do not open and close at tdc, the next cylinder valve opening robs some beneficial positive pressure filling effect developed at end of suction stroke of its neighbour. Effects applicable mainly at wide throttle. By making the conditions of all cyls more similar, mixture does not have to be especially rich as determined by the weakest. Nonetheless very many cars had siamesed inlet ports. Can complicate smooth fast idle.
Similarly in the exhaust. Separation of successive firing cyls avoids a positive pressure from a neighbour arriving at end of exhaust stroke just as the last gas exits. This involves grouping the outer cyls and the inner, the latter can be siamesed as on Minis etc. Further separation is an attempt to better develop and harness various timely negative pressure reflections and concentrate these on one cylinder at a time. Somewhat rpm dependant, and resonant effects can be annoying
Individual pipes are to harness momentum effects and pressure pulse reflections. Because adjacent cylinders fire just half a rev successively, and valves do not open and close at tdc, the next cylinder valve opening robs some beneficial positive pressure filling effect developed at end of suction stroke of its neighbour. Effects applicable mainly at wide throttle. By making the conditions of all cyls more similar, mixture does not have to be especially rich as determined by the weakest. Nonetheless very many cars had siamesed inlet ports. Can complicate smooth fast idle.
Similarly in the exhaust. Separation of successive firing cyls avoids a positive pressure from a neighbour arriving at end of exhaust stroke just as the last gas exits. This involves grouping the outer cyls and the inner, the latter can be siamesed as on Minis etc. Further separation is an attempt to better develop and harness various timely negative pressure reflections and concentrate these on one cylinder at a time. Somewhat rpm dependant, and resonant effects can be annoying