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Discussion and questions related to the course EFI Tuning Fundamentals
Hi! Interesting idea of fuel film. Have never thought about accel enrichment fromm this point of viev. Could you tell me one thing? In carburators is it the same fuel film principle or also inertia of fuel under rapidly changed throttles plays a role?
Carbies have an accelerator pump in them, that is actuated on throttle movement to provide an extra injection of fuel into the airflow on throttle opening.
I know that, thank you. But my the question is more theoretical. I think that in Carb engines there are also inertia of fuel being sucked take place. Here i don't consider accel pump system.
All liquid fueled engines will have a fuel film in play, from a relatively small one in a DI engine, to pretty much the whole internal surface area of the intake manifold downstream of the injection point. Reversion can also cause the fuel film to rise above the injection point.
The further away from the inlet valves the point of injection is, the greater the effect of the injection mass has. On carburetor NASCAR engines, the outside bank on the ovals will run richer due to the acceleration loads dragging the fuel to that side of the engine. If you have a large mass of fuel suspended in the airmass and the throttle plates close, then this mass will continue traveling in the direction that it was going in until another force opposes it. This opposing force could be the valves or the reduction in pressure above the mass, under the throttle plate. When the pressure is reduced the fuel will vaporise more easily as it's boiling point will drop with the pressure drop and tend to migrate to the walls of the inlet manifold.
Stephen, thank for great reply! I haven't thought about NASCAR cars in that way before.