2 replies to this topic

[marion5drsn]

Engine firing Orders and their mathematical limits.
If you use the formula,”8 nPr 7” for an eight cylinder engine the result is 40,320 different ways to fire an eight cylinder engine. However one must remember that this includes the flopping the numbers left to right, fore to aft and rotation about the vertical C/L and the 720 combinations of these.
So I believe that you must divide the large number of 40,320 by 720,giving a figure of 56.
Now you must divide the number of crankpins available which in a normal 90-degree V-8 are four giving a figure of 24. This ignores the balance factors and all of the firings of a 90-degree by 90 degrees crank/block. Most of the different firing orders are only about 4 to preserve the balance order. Many people may become confused by the different numbering systems and say that they all fire different if numbered in a non-similar fashion. This is blatantly not so. The only way I know of preventing this is to make sketches and compare them as then it becomes visually evident which is or is not different. In my mind a firing order that is merely flopped left to right or front to back and or rotated about the vertical centerline is the same, maybe some will differ in their opinions. Am I right or wrong? M. L. Anderson

[desmo]

It seems to me some of the distinctions could become argued in largely a semantic fashion. As V-type engines are laterally symmetric mirror-image firing orders laterally would have little practical difference although if you maintained they were the same you might end up wiring the plug leads wrong! As for fore and aft- perpendicular to the crank axis- symmetry, there are potentially significant issues, one being that torsional vibrations increase in amplitude as they are further from the node (PTO point) thus introducing an asymmetry there. And obviously in a V with an odd number of cylinders per bank such as an F1, while the bank itself may be symmetric perpindicular to the crankshaft axis the balancing masses are most assuredly not. I would be loathe to pare the list of "usable" FOs from what is purely mathematically possible very much based on my knowledge (or lack thereof.)

[marion5drsn]

Have just found the firing order of the Ford V-10 truck engine. Not difficult to do it one can just find the truck manual. The firing order is 1-6-5-10-2-7-3-8-4-9. This is numbered from the Right front being # 1 an Left front is # 6. This is in the manner of the DIN Standard as shown in the Bosch handbook. The Dodge Viper is the same pattern but numbered from Left front being # 1 and # 2 being on the Right front. Since these engines are 90 degree Vee 10s and fire in an Odd manner it makes me wonder if all the V-10s of 90 degrees fire the same? M. L. Anderson