Variable intake manifold makes it possible to optimize volumetric efficiency (VE) over a significant RPM range

Simply put

The idea is to change runner length according to RPM.

Factory made

Here is a [picture of a factory made variable intake] from MembersPage/MarcellGal/EngineSwap/TaskList

It seems that vacuum must be applied at low-RPM (for long runners). Assuming one gear is used that inverts direction of rotation.

The reservoir for the variable intake is fed from the plenum through a check valve. The solenoid is fed from the reservoir. TODO: upload image. The solenoid is apparently same as used for BoostControl, mine draws 285mA from 12V.

What is the round-metallic "2164" thing on bottom-left of the pic?


Thoughts on how to design a variable length intake - originally from Perry Harrington

I think circular movement approach would be the most durable and could be packaged inside a large plenum for filtration.

The intake would be circular, with at least a 180 degree bend between the trumpets and the intake port. You would slide the trumpet side of things inside the intake side.

The sliding portions would be curved in a arc which would permit adjustment of length. The whole unit would use 2 dual output NEMA stepper motors (powered by conventional high current stepper driver) like used on CNC machines. You'd have 4 runners with the arc center being the stepper shaft. You'd permanently mount the stepper body to the fixed portion of the intake and support the upper on bearings.

If you make the arc of the bend large enough, it's possible to see greater than 2 inches of movement. I would make the bellmouths very short on the moving portion to reduce the mass. I would also use light gauge Al tubing or thin stainless.

Another option is straight trumpets with a shallow taper linear screw driven via a stepper. You'd put the trumpet inside a plenum, this would have dual effects when adjusting the length, you get a longer runner, but with the longer runner you reflect off the plenum wall more aggressively because the mouth is closer to the wall. This could aid in cylinder filling at low rpms.

factory made variable pipes:


See also