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Jaguar V12 Auxiliary Air Valve Differences

Jaguar V12

Auxiliary Air Valve Variations

Due to the various configurations of the engine itself, the EFI system, and the emission controls over the years, the AAV has had to be varied to provide acceptable cold start performance.  Due to the nature of the design, any amount of airflow desired at any temperature up to operating temperature can be provided by merely revising the shape of the port in the side of the cylinder.  The same bulb can be pushing the same piston against the same spring in any iteration; as long as its motion is related to temperature, a port shape can be devised to provide the optimum cold start performance.

Of course, if the owner starts fiddling with his engine, operating it with low-temp thermostats, removing emission controls, or pretty much any other modification, the amount of air provided by the AAV may no longer suit the conditions.  This page presents photos and/or illustrations of the cylinders from various part number AAV's so that tinkerers can make informed decisions when trying to purchase a different AAV or modify the one they already own.  It may also help those who purchase AAV's from the junkyard and then find they have the incorrect version and would like to know what the differences are.

Data is arranged in sequential order of part numbers.

Note: the distance from the inside bottom of the piston to the upper edge of the piston -- which is the part that slides over these ports to cover them -- is 19mm.  In other words, when the inside bottom of the piston is 70mm below the upper edge of the outlet fitting (as it is at room temperature), then the upper edge of the piston is 51mm below that same datum.  At least one dimension on each illustration of a port below is taken from the upper edge of the outlet fitting, so using Sawyers' AAV performance chart (reproduced at the bottom of this page for reference) you can figure out where the piston is going to be at any given coolant temperature and how much of the ports it's going to cover.

Craig Sawyers provided this illustration of the cylinder from AAV part number 73192:

This is the cylinder from AAV part number 73225:

Shamelessly plagarizing Sawyers' illustration and altering it to represent this part:

The upper edge of this port is interesting; not only does it have that funny scalloped shape to it, but it's also about 2mm farther up from the bottom than the other ports shown on this page.  In other words, when the engine has warmed up enough that the other ports are closed, this one is still a bit open.  Roger Bywater suggests that this design may provide a sort of automatic idle speed correction at operating temperatures.

This is the cylinder from AAV part number 73352:

Can't even get the entire port in the picture, since it wraps fully 180º around the cylinder.  The pic was taken a little to one side to show one end of the slot; the other end looks exactly the same.  Clearly, the engines this AAV came on needed all the air they could get when the piston was below that slot.

An illustration, again made by revising Sawyers' original:

It should also be noted that the horizontal slot is located closer to the bottom of the cylinder than the openings on other ports; the upper edge of the wide slot is lower than the horizontal edge at the bottom of the 73225 port shown above.  This means that, after other AAV's are fully open, this one will continue to open farther as the temperature continues to fall.  In fact, at room temperature the wide slot should actually be closed by the piston; you will need to get this unit below freezing to see the port fully open.

As mentioned above, here is the AAV performance chart provided by Craig Sawyers:

Chart Jaguar V12 Auxiliary Air Valve Piston Motion

The dimension described along the left scale in this chart is easy to measure, even with the AAV still mounted in the car.  For comparing against the illustrations of the ports on this page, you would need to subtract 19mm from this scale -- the distance from the inside bottom of the piston to the upper edge of the piston.  This will give you the location of the "closing edge" of the piston in relation to the port at a given coolant temperature.

It is believed that this chart will apply to all AAV's regardless of part number or port configuration.  At least, all AAV's on which the bottom of the bulb is marked "-30º".

If you have an AAV that doesn't appear on this page and would like to add it, there are a couple methods.  First, if you don't want the AAV in question, you can send it to:

    Kirby Palm
    3 Wanda's Way
    Havana, FL  32333
    +1 850-539-7775

and I'll tear it apart, take pictures, and add them to the page.  I cannot promise to return the AAV, though, in either working or non-working condition.  If you'd like to negotiate that, you can write to me.

Another method, of course, would be for you to take it apart yourself, take digital pictures, and send the pictures to me.  Be sure to mention the part number, please.


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