The intake manifold is the part of the engine where the air that is sucked through the airfilter is collected and divided among the cylinders.

And although it is roughly made out of 1 piece of casted aluminium, we can still name a few differents parts of the manifold.

In the picture above, you can see the completely disassambled intake manifold of my Bigport 4A-GE. In the background, you can see the throttlebody that is usually bolted onto the manifold.

As you can see, the manifold doens't consist of much more than the collector (Sometimes also called the Plenum) to which the runners are attached.

The Collector really isn't much more than a sort storage/buffer for the air to collect. You might wonder why the air isn't directed right into the runners and why the collector has this shape and size. This is to reduce pressure waves to the rest of the intake system and to make sure all the cylinders have a good airflow. If the collector wouldn't be there, the last cylinder might be starved of air because the airflow is directed of disrupted by the first cylinder it encounters.

A look into the Collector just after I cleaned it

The 'pipes' going from the collector to the cylinderhead are called the runners.

You might have looked at a picture of the intake manifold and wondered why they're not just straight pipes going to the cilinderhead. Most people don't even realize it, but  a great deal of thought has gone into those simple pipes! Their shape and length can even help make the engine more powerfull or efficient.

I'm going to try to simplify and explain something pretty complicated.

 To let air flow into the cylinders, the intake valves will open and the air is sucked in. When the intake stroke is finished, the valves will close again. Now you can imagine that when the valves are closed again while the air is sucked in, a pressure wave will be formed by the sudden change in pressure.

That pressurewave will go back up the runner, to the collector where it will 'bounce' off the walls of the collector and the throttleplate etc. and eventually it will find it's way back into the runners.

This process takes place a few hundred times a second so a pulse is formed that travels back and fourth between the intake valves and the collector.

That isn't always a good thing. Air going into the cylinders could meet that pressurewave going in the other direction what really messes up the airflow. There is nothing that really can be done about it. As long there are valves going up and down, there will be pressure waves.

But luckily for us, those pressure waves can also be used to benefit from them.

If the pressurewave travels from the collector to the cylinders right at the moment that the intake valves open, the pressure wave will force some extra air into the cylinders.

To get back to the shape and lenght of the runners. When they have a certain volume and lenght, engine manufacturers can predict how long the pressure wave will take to travel through the runners.

When we know that, we can 'tune' the runners and collector to profit from the pressure waves at certain RPM's when the pressurewaves will be in sync with the opening times of the intake valves and thus forcing air into the cylinder every time they open!

The Bigport 4A-GE engines have a additional feature in the T-VIS system (See the article dedicated to the T_VIS system elsewhere on the TechTalk pages). This is an additional trick Toyota pulled on the 4A-GE Bigport engines to create some more torque down in the rev range, where these engines really need it.

As you might have noticed in the pictures above, the 4A-GE Bigport intake manifold has 8 runners, instead of the four runners you would expect on this four cylinder engine.  That means that there are two runenrs for every cylinder.

The T-VIS system has a valve in every other runner (So for the two runners for each cylinder, one is closed of with a butterfly valve) This effectifly changes the lenght  of the runners for that cylinder. This affects the presurewaves in a positieve way to create just that little bit more torque, we would be lacking otherwise. When the rpm's go up, the pressure waves will change frequency and the engine will need more air going into the cylinders. To counter all of this, the ECU will activate the T-VIS system, and the valves in the runners are opened (at 4350rpm) to let more air in and change the frequency of the pressure waves so we can profit from the again! I think it's a very clever disign and it gives a nice little kick in the butt when the system is activated.

So there you go. There is a lot more to that simple intake manifold than you would think!