986 Forum - The Community for Porsche Boxster & Cayman Owners - What's the function of the Venturi Tube on a Tiptronic?

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- - What's the function of the Venturi Tube on a Tiptronic? (http://986forum.com/forums/performance-technical-chat/56336-whats-function-venturi-tube-tiptronic.html)

Quote:

Originally Posted by KRAM36 (Post 441071)

Went out and disconnected the line to the brake booster. It works opposite of how I thought it does. The line to the brake booster pulls air from the booster, a massive amount of air. So the engine isn't losing air, it's getting air added to it.

So you have the venturi tube adding air and the AOS adding air after the MAF sensor, how does the ECU actually know the amount of air going into the engine?

Not quite. The brake booster is a closed system. The booster uses the force of the vacuum to move a diaphragm when you apply the brakes, but is not open to allow intake of new air. The volume of air passing the MAF is still to TOTAL volume of air being drawn for combustion (Except for the SAI system).

There are some good "How it Works" diagrams and videos if you Google it.

You got me curious about the whole venturi tube. Why just on automatics and what does it do....

It seems like it is common on German cars: VW, Audi, BMW, and in most applications the venturi is called a "suction jet pump".
There is some good reading about it:
How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail? - Bimmerfest - BMW Forums

Post #4 in this thread addresses it: *DIY* - B5 1.8T Vacuum/Check Valve/SAI/PCV - Delete & Simplification

Ok, yes that makes sense. So the venturi tube basically has zero affect on the air volume to the engine?

So do the O2 sensors sort out what the AOS does? The AOS adds air and gases, correct?

Never thought about the SAI. From what I saw during the intake work, it looks to be pretty crucial to the operation of the engine and Tiptronic trans. Not sure how people delete that?

The SAI is an emissions control device and only runs for a very short period at start up. Apparently this is only in North American cars and doesn't exist in ROW cars. It can be deleted by flashing the ECU but the file is different for tiptronic cars than for manual cars. It doesn't seem to affect the performance of the engine, only the emissions at startup.

The venturi keeps air speed up during gear changes with the tip. Removing it will create a loss of performance between gear changes, especially between 4-5 gears.

Whhoooo. A loss in performance. I think that is a no go for KRAM36. :D ;) :cheers:

Quote:

Originally Posted by Jake Raby (Post 441353)

The venturi keeps air speed up during gear changes with the tip. Removing it will create a loss of performance between gear changes, especially between 4-5 gears.

Jake thanks for the input. What would happen if I moved the port that goes into the intake pipping to the air box, like this?

http://i58.tinypic.com/16c191c.jpg

Move it to here? This would also allow me to use larger pipping and not worry about putting that connection into it.

http://i60.tinypic.com/rvbpds.jpg