Why are Turbo 4cyl engines Fuel efficient and V6/V8 Turbo’d engines not equivalent or better?
In: 5
It mostly comes down to volume of fuel needed to reach the ideal fuel to oxygen ratio in the displacement of each cylinder. More volume means more fuel. Attempts have been made to only use 4 cylinders on an 8 cylinder engine under certain circumstances, but this still requires all of the extra spinning mass of the pistons, pins, rods, counterweights, and the resistances in the valvetrain.
In addition, a low cost unified air intake manifold must be sized for the maximum flow potential of the full engine displacement. The large volume in this area reduces air velocity at lower engine output speeds. The lower velocity air reduces mixing in the cylinder at lower output power. This results in poor fuel economy while cruising, which is the primary state most automotive engines operate. Peak efficiency involves optimizing flow in these low output situations. Most 4 cylinder engines require fewer compromises when it comes to air flow into and out of each cylinder
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