Aux Vents and Stacks

[Clatter]

Trying to do some searching.. But it's not turning up.

I'm finishing up doing my carbs - a set of 44 DCNFs.
They are going into my Fastback, and until the (type 4) motor is in, i won't know how much room i have.
It will be a bit more than a regular type 3, but not a lot, like in a Bug or Bus..

Anyways,
Looking at the pics above, the aux vents stick up into the stacks.

Do the stacks act in conjunction with the aux vents?

Looking at them, it -seems- like some relationship might be at work.

If i cannot run stacks due to clearance issues,
What kind of changes will i be looking to make to the aux vents, if any?
Pierce has a bunch of shorter ones..


Additionally, how much room above the top of the carb body, or stacks, or even the top of the aux vent should i consider minimum?


Lastly at what point does having stacks choke the motor when the cleaner lid is getting too close, and you're better off without stacks?


Bunch of questions..
Any experienced advice is much appreciated.
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Bus Motor Build

What’s That Noise?!?

[modok]

The extended aux vents were used to improve WOT low rpm metering when using wild cams. it both dampens/steadies the signal to the main well.
It is probably BEST for the top of the aux vent to be just below the bellmouth of the stack, to get a consistent airflow into them, free of any random currents that might exist up higher in the filter housing, BUT it isn't critical, it would work if they were above or below probably.

If you do not need extended aux vents for this purpose... then fitting shorter ones is a fine idea, and will probbly need just slightly smaller mains jets.

While it is possible to shorten them, I think the best thing to do would be fit shorter ones, and sell the long ones to me and re-coup most of the cost

In theory, the airflow to the stack would be OK as long as the gap is .25 times the ID of the stack or larger. "key word there being "airflow"
HOWEVER, in practice up to 1.5 diameters may be needed to prevent fuel fog impinging on the bottom side of the lid. or to put it a better way, if the JOB of the stack is to contain the standoff, and your space is limited.... it's more effective use of the limited space, to use a shorter stack with a big gap above than a tall one and a small gap above.
How far the fuel fog will BE, above the venturi, is a function of the runner length and cam timing, and a few other factors.
long manifolds and wild cam timing will have the craziest reversion fog!!