No blow backs in closed loop systems?

Not necessarily. Sequential injection will be a closed loop system, and about as blowback free as is possible to get. But you can have simpler systems that are closed loop too.

The important thing is to fill as little on the inlet tract as possible with an explosive mixture. Injectors placed next to the inlet valves, that only open when the valve is open, achieve this well. But a simple mixer must be placed upstream of the throttle valve (I have seen one attached to the airbox outlet, several feet from the inlet valves), and so much more of the tract is filled with mixture. The 'closed loop' is a way of accurately controlling the ratio of the mixture.

IME, in the absence of sequential injection, the most important thing in reducing the occurrence of blowbacks is to make sure all the HT components are in first class order.

In message , BW writes