Question about AAV

The Auxiliary Air Valve when it’s open (cold) the orifice or the opening is about 4mm to 5mm for the air to go through. So, why is the the vacuum hose attached to it has a 19mm ID, is it more for air volume?

 

Great question!

 

It's just to ensure that the valve in the AAV is what controls the airflow, not the pressure drop in the hose -- and Bosch designed it for being used on other marques so maybe not so necessary to be so big on Ferrari, but maybe more important on others that have very long AAV hoses. Are you sure about that 19mm ID size? My "I'm-not-going-to-check-it-off-hand-memory" is that it's more like 15~16 mm ID hose.

 

Steve, I just measured the diameter and it is 19mm.

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Ack!!! - You've proven once again, Mike, that my "I'm-not-going-to-check-it-off-hand-memory" is often wrong.

I went thru my files and found this picture of a 308QV AAV ...229 with a file name of "AAV cold..." so probably just out of the freezer (i.e., 0 deg F), but shows that the opening can be pretty large and the ID of the 19mm hose fitting isn't much larger:

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Well maybe that’s is the difference between having the AAV coming right out of a freezer and and an AAV that sits overnight with a 50deg F to 60deg F average temp. If that’s the normal opening size then maybe you’re right 19mm vacuum hose isn’t much.