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Al Gietzen wrote:
As I see it; injection at the ports is good for cold starting. Injectors some distance away from the ports gives better vaporization. Injectors too far away from the ports; like maybe more than a foot or so, results in liquid fuel on the runner walls, especially when cold or at lower rpm. I think Mistral found this out when they initially had the injectors quite a distance from the ports.
Megasquirt calls this phenomena Tau, and they have a setting to control it. When you cut the throttle, the engine will pull in some of the "sidewall fuel" and run rich for a moment. If you goose the throttle, some of the extra fuel will be depositing on the runners instead of powering the engine, making it run lean for a moment. The control setting will add or subtract fuel as needed to make for smooth transitions. They can't just use a static setting, because it is dependent on a lot of variables like injector size and runner length.
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