Plenum Options for 4.6 Ford V8

Above are the two plenum options we offer with the 4.6 ford throttle bodies. The one on the left is the stock mustang piece ported and on the right is the raised plenum design.

When designing a plenum for maximum performance there are a few considerations. Cross sectional area, how straight the air flow is, and velocity of the air. You have to balance out the three for the best performance. If you simply hog out as much metal as possible you are making the largest area inside the plenum however you sacrifice the velocity of the air coming through.

For the ported stock plenum we match the throttle body and open up the casting throughout which is a nice increase in power and flow over stock.


It is best to match the inlet to the throttle body and then to straighten out flow as much as possible. it makes no sense to make the inside of the plenum bigger then the throttle body since this will simply hurt velocity and not increase volume, the throttle body would be the limiting factor in flow. This straightening is where the raised plenum helps.

 

If you look at these two next to eachother on the stock mustang throttlebody you can see the air has to make a 90 degree turn. On the raised version it is a much more gentle transition. This keeps the velocity and airflow up.

To further straighten flow we port the edge of the opening into the intake to the edge of where the gasket will sit. The short side radius (inside corner) is also ground down about half an inch in the center, increasing cross section and decreasing the sharpness of the transition.There are some aftermarket versions like the picture below that greatly increase the area on the top

As you can hopefully see this actually does the opposite of straightening out flow!

The vacuum lines are routed in a slightly different manor on the raised plenum and it has one extra port. Please do not order this if you are not comfortable with re-routing the lines a bit. It is easy enough to do but worth mentioning.