Re: The Vipers\' Double-Piston Firing Sequence
Every one has a small piece of the answer but let me try to help answer the question "Why does the Viper engine sound the way it does"..well to start with..there is a pulse (tone) ring on the crankshaft that has five groups of two notches equally spaced apart at the outer edge. Each group of notches will represent a signal for a specific set of pistons. The PCM will determine the basic timing by looking at the falling edge of the slots. Each corresponding slot is 72 degrees apart and 3 degrees wide and there is 15 degrees between each slot in the pair.
The falling edge of the first slot, of each pair of slots is used for cylinders 10,4,6,8,2. The second falling edge is used for cylinders 1,9,3,5,7. There are five sets of paired cylinders: #10 and #5,#9 and #8, #4 and #7, #3 and #2, #1 and #6. It could take the PCM one full engine revolution to determine the crankshaft position when it is cranking.
Since the V10 is a 90 degree block, the combined angle of the bore center lines of the opposing banks will be 90 degrees, which means that a piston will at TDC every 90 degrees. Sooooo for each cylinder to fire, it would take 900 degrees of crankshaft rotation and no matter how you do the math....that won't work. So to match the crankshaft rotation, it was necessary to make it an "odd fire" engine. That means that the cylinders are not fired at the same crankshaft angle. Five of the cylinders are fired at 54 degrees and the other five are fired at 90 degrees which adds up to 720 degrees or two complete crank revolutions. This is why the notch edges are at different degrees since the spark will be staggered. Ok, so I have expanded on Marv S's answer... now lets expand on Doug's answer.
A DIS coil can be arranged in various alterations of polarity. This means it does not matter if the spark fires positive or negitive as long as there is enough voltage to jump the spark plug gap. As the primary flux collapses through the secondary coil windings when the primary coil is interruped, a high voltage potental is created. A quick interruption causes the flux to cut through the secondary windings faster which means a quicker interruption results in more secondary voltage than a slow interruption. Dwell (spark timing) is constant, at low RPM based on battery voltage. A constant dwell allows constant voltage at the coil for a constant spark. But at high RPM, there isn't time for full saturation of the coil. So the PCM will change the primary duty cycle from 100% to 80% to speed things up.
The voltage will leave the coil tower for example, #1 and travel through the wire to the #1 plug, through the center electrode, jump the gap to ground. This would be the cylinder that is on the compression stroke. This will require about 10-15k volts of the 40k potential from the coil. The companion cylinder, #6 will be the wasted spark cylinder. To complete the series circuit back to the coil, the remaining 25k volts travels through the block to
the #6 plugs ground, and jumps the gap. This will take about 1-3k volts. The circuit is then completed through the spark plug wire back to the coil pack.
When cylinder #6 goes to the compression stroke, cylinder #1 is on the wasted spark stroke. But the voltage from the coil takes the exact same path due the polarity of the coil. There is more than enough voltage to fire the plugs at any RPM.
Hope this helps. BTW
Hey Jeff question for you.......did you get the curtains up in the trailer yet?????
