:number1 I just ordered a book about it today. I understand firing when the valves are closed but it is still thought to be favorable in high performance apps because the time to fire off an injector decreases as the rpms start to climb. I also found that sequential systems that are used with a performance cam that has 220° of intake duration with. 050 valve lift can only inject ~ 60% of the fuel that a identical batch system can. Which basically means you need to run bigger injectors with a sequential setup in order to get the best fuel delivery.