# B Volume of air flow through an orifice at speed

#### motolectric

Trying to figure out how much air can (or would) flow through an air intake on a vehicle.

I have a rectangular intake opening that is 13.52 square inches, the vehicle is traveling at 60 MPH for 1 hour.

Obviously more air is being forced into the intake due to the speed but I can't sort out how to calculate that.

M./

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#### russ_watters

Mentor
Trying to figure out how much air can (or would) flow through an air intake on a vehicle.

I have a rectangular intake opening that is 13.52 square inches, the vehicle is traveling at 60 MPH for 1 hour.

Obviously more air is being forced into the intake due to the speed but I can't sort out how to calculate that.
Air intake for what? The backpressure from whatever the intake is to will determine the [change in] flow rate.

#### motolectric

Hi,

Essentially there is no (or little) back pressure as the housing has vents for any excess pressure.

I have attached 3 graphics.

The first shows the calculations for the amount of air/fuel mixture the engine would injest.

The 2nd shows the orifices I am dealing with.

The 2 red boxes represent the 2 intakes at the front of the hollow cast aluminum frame of a motorcycle.

The 54 mm red circle is the intake to the fuel injection system.

The housing has both the 3 vents seen to the lower left and a tubular vent to the rear that is not seen in this image.

The circles and rectangle at the top are from the conduit from the frame to the airbox housing and it is plain to see that they are large enough to flow enough air for the 54 mm fuel injection system.

The issue I am trying to resolve is whether there is excess pressure (and how much pressure) in the housing (it is sealed other than the inlet at the top and the vents I described.

I say there is and others say there isn't. This is as far as I have gotten.

On the bike, at 3,000 RPM in 4th gear you are doing 60 MPH so that is the common variable.

Some people encourage buyers of the vehicle to change to a fully open airbox stating that the OEM is "restrictive".

I claim that not only is it not restrictive but that in order to make use of the excess airflow the engineers put in the vents to use the excess airflow to cool the cylinders.

The air would not be expected to flow outward unless there was some pressurization inside the airbox enclosure.

Again, thanks for any tips or info on solving my problem.

WD./

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"Volume of air flow through an orifice at speed"

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