It should be remembered that there is little airflow and velocity in the port and runner until the valve is open a fairly significant amount. As such, true, timed, sequential systems must have larger injectors fitted for a given hp. 050 valve lift, the sequential system has only 61% of the time to inject the fuel as the batch fired system. On an average performance cam having 220 degrees of intake duration measured at. This is determined mainly by the camshaft characteristics. The batch fired system has the advantage of being able to inject fuel for the entire period of crankshaft rotation whereas the timed system technically only has the time available that the air is flowing in the intake runner. This is true whether the system is timed to valve opening or batch fired. As rpm increases, the amount of time available to inject the fuel decreases. Rpm's are generally much higher, fuel flow rates are much higher and emissions usually take a back seat to power output. Performance applications are somewhat different from stock applications. The timed concept was developed mainly for tougher emission laws and EPA cycle testing where much of the cycle is run at low rpm and part throttle, where the time available to inject is long and the injector pulse is short. Some people are dismayed that anyone would use the batch fired method however, there were tens of millions of Bosch and Bosch derivative systems sold in the '60s, '70s, and '80s which worked just fine using batch firing. In effect, the fuel sits in the runner for a short period of time before the valve opens and the airflow carries the mixture into the cylinder. The other injection strategy is batch fired where several injectors are triggered simultaneously and not timed to the intake valve open period. This is supposed to mix fuel and air better and reduce manifold wall wetting. The idea behind this is to spray fuel only when airflow in the intake runner is established. A better term would be timed, implying that the starting and finishing of the injection pulse is timed with the intake valve opening. ![]() Technically, all EFI systems are sequential in that once all cylinders have been injected, the sequence starts from the beginning again.
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