A typical V8 fires every 90 degrees of rotation and some would call this an even firing engine. Every "pop" is evenly spaced from the next one. On the Viper, since the block angle is 90 degrees and we have 10 cylinders, the crank pins are spaced 72 degrees apart.
To understand why the viper sounds the way it does, (different from a V8) imagine the rotation of a single crank pin... one of the pistons hits TDC ... then exectly 90 degrees of rotation later, the other piston (on that same pin) hits TDC. On a V8 where the crank pins are 90 degrees apart, another piston will hit TDC after another 90 degrees of rotation. But on our Viper motors, since the crank pins are 72 degrees apart, between 90 degrees of the first piston and second piston hitting TDC, another piston of one of the other crank pins must hit TDC. This is why the Viper is called an uneven firing engine.
Another example is comparing the sound of a Harley Davidson with a Honda twin. The Harley, like the Viper is an uneven firing motor. The Honda is an even firing motor.
The Ford Cobra concept car uses a V10 and it sounds awesome. But the engineers have worked to get the sound just right...
"Getting a V-10 to sound right, given its naturally offset firing order, is tough; the Viper pipe-benders have struggled with it for years. The Cobra's starter sounds like a meat grinder, but once the one-off, 6.4-liter, all-aluminum, 600-horse DOHC V-10 lights up, it's magic. The big-inch exhaust note burbles like an expensive speedboat at idle, and rises to a considerable whoop as the revs come up. The closest noise analogy I can come up with is a Lamborghini Gallardo with the mid-range cranked up to 11. Or a turbine-powered industrial vacuum cleaner. The pipes exit out the rear, which probably helps balance the exhaust note, but one has to wonder: what would it sound like with sidepipes, a la Cobra 427 S/C?"
Here is the link to the article quoted above...
Ford Cobra Concept
