 |
|
|
1994-2002 [Subscribe to Daily Digest] |
There are three pressure losses associated with the snorkle tube.
1) entrance losses
2) friction losses along the length of the tube
3) exit losses where the kinetic energy of the flow is lost.
1) The larger the opening, the lower the entrance losses. The bell mouth helps a great deal as a straight cut pipe is the worst condition.
2) These are small and can be ignored. The losses will go down with a larger pipe with lower velocities.
3) For a given flow rate, the velocity of the flow will vary with the ID area of the pipe. To get the outside air to go through the pipe, it must be accellerated to a velocity. This accelleration requires a force or pressure. The pressure drop times the flow volume represents work. The kinetic energy of this flow is lost as the air exits the tube and encounters the filter. If you double the flow cross section you cut the velocity to 1/2 of the original. The kinetic terms vary as the square of the velocity. So the forces and pressure loss drops by a factor of 4. As the flow rate does not change, the mass flow rate is the same.
So it is more complicated that this, but those are the major considerations. You never want to accelerate a flow with a small inlet tube as this will generate dynamic pressure drops. Saab put in the 2" x 15" snorkle tube to act as a silencer. They use the flow dynamics to filter out turbo whine sounds. It is a low pass filter. So it is really a flow muffler in the stock form. It was not designed for optimal performance. They also put in a turbo compressor discharge silencer which also creates a smaller flow section and more dynamic losses. That needs to be removed. And the throttle body transition casting has a sharp edged ID restriction, creating entrance losses, dynamic losses and horrible turbulance. Grind that out and you get more power and the engine runs smoother too. The turbulance creates uneven fueling and cylinder charging. The turbulence probably has some nasty interactions with the throttle plate in the throttle bore. So the induction design on the NG900 turbo's was driven by noise considerations, not performance. The transition casting design was a farse.
posted by 207.43.19...
, Mon, 12 Nov 2001 17:26:19, Tue, 13 Nov 2001 10:10:53, Tue, 13 Nov 2001 11:02:08, Tue, 13 Nov 2001 11:06:51, Mon, 12 Nov 2001 20:42:02, Tue, 13 Nov 2001 09:29:36
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
