Thread: If you could make your own intake manifold

sort of...yes^^ I'm still trying to understand the idea of the stacks sticking out into the plenum rather than blending smoothly into the bottom of the plenum. Either way would work good i'm sure. I know that some of the superbikes even make two of their stacks longer than the others, instead of all equal length, and the newest ones actually adjust the length of the stacks as the motor reaches higher rpm's...sick.

There is a picture I saw a long while back that showed exactly why you want the stacks to stick up into the plenum instead of being flush. It was a pressure map showing pressures around a bell mouth.


I haven't been able to find it since though, and I look for it occasionally.

The low pressure area around a bell mouth is in the shape of a mushroom and it curls under the lip of the bellmouth. This means that the pipe is drawing air from around and under the lip of the bellmouth just as strongly as it draws air from above it. When you allow the bellmouth to stick up into the plenum, you're allowing air to be in those low pressure areas to draw in. When you make the bellmouths flush with the plenum, you're loosing the opportunity to put air in one of the spots in which it is the easiest for the pipe to draw it in.

You know, it's funny. You asked the same question and I tried to explain it to you in another thread.

http://www.sr20-forum.com/317694-post16.html

I feel that finding the pressure gradient around a single bellmouth is the key to convincing people. It is just hard to find.

One other thing to mention that @Andreas Miko pointed out a long time ago in one of these intake manifold threads was that the pipes leading into the intake are just as important to get right as the manifold itself.

You can design a good, even flowing intake:


And then have it ruined by the piping that leads up to it:



SEX!! with a Carbon fiber Intake Manifold - Mazdaspeed Forums

annnnnd Ben just blew my mind haha

Now in the second picture. Is it bottlnecking the airflow? What is causing that high pressure zone? "I'm going to make up a set of air straighteners in the mani"

you're going to have higher velocities the closer the air gets to the head. You are taking roughly 2" round runners and dividing them up into two's. It's creating a venturi right about the point that the fuel is being sprayed in. Bottlenecking is not always a bad thing. High pressure wants to be low pressure and can be used to your advantage...or disadvantage.

The second picture is highlighting that the piping before the intake is causing the air to highly favor the left side instead of being equal like in the fist picture.

This happens because air has mass and is compressible. As the air flows around the 90-degree bend right before it enters the intake manifold it tends to gather up on the outside of the turn. Because of this, the left side of the manifold gets much more air entering it than the right side. The air entering the manifold also has inertia forcing it in that direction as well.

anyone know where to find bellmouth velocity stacks at a good price? $32-$40 a piece seems awfully high for something so small.

check this out.

World Of Mysteries: There’s a Giant Hole in this Dam Water! [Bell-Mouth Spillways]

could you imagine fishing and not paying attention and getting sucked into that wowww