The effect of the size of the intake manifold on a forced induction engine?

Theoretically speaking, a smaller intake manifold would mean higher pressure, which would then cause the air to enter the cylinders more "aggressively" at lower engine speeds but cause more resistance at higher engine speeds. And then a larger intake manifold would have a lower pressure in it so it would rely more on the vacuum created by the cylinders going down at low engine speeds but would have very low resistance at high engine speeds.

But how true is this?


For example: say our turbo moves 33 liters of air per second. In intake manifold 1 with an internal volume of 1 liter, and an intake manifold 2 with an internal volume of 2 liters, intake manifold 1 will have a pressure of around 34+ atm (absolute pressure), while intake manifold 2 will have 17.5+ atm (absolute pressure), meaning that at the same engine speed, the same engine with the smaller intake manifold has twice as much pressure inside which should technically push more air inside.

4 Answers

  • 6 months ago

    The intake manifold does something you are not considering. It heats the intake fuel/Air mixture. So does super charging. You don't want to increase the size too much.

  • 6 months ago

    With forced induction the effect of the size on the intake is negated. Larger intake manifolds mean more time to get boost full in the case of turbo chargers.

  • 6 months ago

    For a naturally aspirated engine you always want the intake to be as large as possible because that will deliver the most air to the cylinders. You need to think in terms of the pressure at each intake valve. You want that as high as possible in terms of absolute pressure.

    With a blown engine the size of the intake is not as critical but you still want it as large a practical.

  • Anonymous
    6 months ago

    not much ..................................

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