dual port manifold ends -- what's with the notch?

What, no one else wondered about this, too?

I've often wondered myself, but never spent too much time on it. It's just like the gaskets for the intake end castings, there is a hole punched in the gasket between the cut-outs for the ports to the head. Why? It's just a solid casting under that section of the gasket, so what good does the hole do?

You can see it here:

Chris

some of the factory heads had a locating dowel for the intake manifold...that's why there is still holes in the gaskets...(I've only owned one vw with the dowels, so i have absolutely no information on years, etc...mine was a 71, the first year of the dual port...maybe something they had but later deemed unnecessary...)

From what i read years ago(sorry no source) the notch in between the ports is to help with the reverberation that happens when the intake valve closes.... never gave it much more thought after hearing that....my aftermarket intakes don't have it, but they are designed for port on port so it wouldn't make sense...

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I have them on my 1300 cc AB engine too. Pretty hard to get the old gasked out due to that dowel. It´s also a ´71. The old AR engine (´73 ) has had them too if i´m not mistaken...

Roger

I always thought they were there as part of the intake 'tuning'. To damp down reflections when the valves close etc. sort of like how you tune an exhaust by linking the rear pipes ?

never seen a dowele'd bug so wouldn't know about that

Rich

I believe the type 3 heads came with the dowels.

Good to know..I've not encountered it yet but explains the hole. After all, why make two versions of the gaskets if you can make one that will work for everyone.

I guess with dual carburetors and a setup where each cylinder has it's own venturi it wouldn't really matter if the notch was there or not. I don't recall seeing that notch on the intake manifolds for the webber IDF 40's I had years ago.

Might be interesting to see if a synchrometer would give a different reading(read: needle/float jumping a bit) with the notches blocked on an otherwise stock engine.

Chris

i'd say it may affect the idle quality....somewhat similar to dual kadron carbs needing the "balance tube" that runs from manifold to manifold... just a guess on my part...