In 4-stroke engine, each cylinder needs to fire once per every two revolutions. In a cross plane V8, this means that a firing event occurs every time the crankshaft moves 90 degrees.
Our V10's are a little different because each cylinder still needs to fire once per two revolutions, but can't do it in 90 degree intervals (90 degrees X 10 cylinders doesn't equal 720 degrees of rotation). So, the Viper V10 has a firing event at 90 and 54 degrees. This creates an uneven buzzing type exhaust note.