Question why intake manifolds are twin chambered with Slot

[ian4455]

Can someone explain why an intake would be twin chambered and have a slotted section between both chambers ?

[Wheeljack]

simply put, it theoretically creates a stable volume of air at the entry to the runners, which provides for uniform pressure at the tops of the runners. this makes equal cylinder to cylinder flow. this stable volume, or plenum, is separate (via a restriction, or your slots) from the moving turbulent flow coming into the manifold--this can cause cylinder to cylinder variation.

that said, there are very sufficient single plenum designs that produce high hp.

[JP]

The dual chamber manifold principle is used to equalise flow along all the runners on the intake whlst retaining a small intake plenumb volume for quick throttle response. Where the theory is that by pressurising the first smaller chamber and allowing the air to exit via a slot along the length of the bigger chamber that hosts the runners you allow even flow distribution to each runner.

So long the cross sectional area of the slot is no smaller than the throttle bodies then there is no restriction so to say. The purpose of the slots is to act as flow stabilisers.

Unfortunately the twin chamber design introduces it's own complexities with regards to turbulence, which means if done incorrectly like many I have tested on behalf of certain companies make the flow distribution worse than a single plenumb manifold.

If the flow straighteners (grooves/partitions/slots etc..) are placed in the correct locations they counteract the turbulence caused by the transition between the two plenumbs to help equalise flow amongst the runners.

As a reference point a large plenumb chamber with a correctly designed taper and throttle body position is capable of flowing almost near perfect flow distribution amongst it's runners.

However the downfall is that the turbo has to shift more air to fill the plenumb and build up pressure before it sees the engine resulting in what people describe as lag. By utilising a correctly designed twin plenumb design which utilises a smaller plenumb volume you can get the same even flow distribution whilst benefitting from quicker throttle rsponse. Ideally suited to track cars that have to go in and out of corners a lot. Whereas the single big volume chamber is more suited to Drag racing where it benefits from the ability to hold boost better till redline.

If you want to throw a real spanner in the works you can now tune the runner lengths/trumpets to the correct harmonic relative to your engine capacity rpm and cam profile to free up further flow into the engine. As achieving the correct 2nd/3rd order harmonic will assist flow into the engine whereas anywhere inbetween will create harmonic turbulance by introducing shockwaves that the airflow has to overcome resulting in the manifold never achieving it's laboratory ideal test figures in the real world. This is ultimately always going to be the downfall of any mass produced manifold as not everyone runs the same engine configuration, so it always has to be a compromise, where some people are going to be lucky and some not.

hth JP

[ian4455]

thanks, great information.

[repo]

Twin chamber is especially preferred in high power low boost apps. Less boost on same power means more flow speed. More speed means more inertia.

Usually also the room in engine bays limit the possibilities of designing a proper single chamber.

[Lupo911]

Twin chamber is especially preferred in high power low boost apps. Less boost on same power means more flow speed. More speed means more inertia.

Usually also the room in engine bays limit the possibilities of designing a proper single chamber.