[RAIIIJudge]

Happy 4th, everyone ..

How and where exactly is QJ receiving fresh air from RA system?

The two vacuum activated circular flaps in hood pan open ... directly into the two enclosed areas of RA foam. But is fresh air also entering carb via the large open area between those hood-flaps, directly over where air cleaner lives?

If yes ... whats the point of flaps opening into that isolated area of foam?

Also .. I've got that tube that comes up off exhaust manifold shroud but have been hesitant to put it back on motor cause I dont run a choke and I dont want the extra heat up there. Is that a real concern? I wonder if hose should be avoided, if there's any point in closing up opening at underside of pan where hose attaches?

(sorry for pic size! been trying to figure out how to embed pics directly into post)

[Formulajones]

On the heat riser I always keep it looking functional for aesthetic reasons but I have the tube blocked and stuffed with aluminum foil.

The scoops work surprisingly well on the 69 despite being small and in the middle of the hood. With a inlet temp sensor I can watch the temp come down when moving and nearly match outside ambient temps within a couple degrees after moving for a couple miles.

[RAIIIJudge]

So tube's being blocked by wadded up tinfoil inside tube alone? Or is there something else involved?
Unused shroud does bug me so I'd like to get that thing back on there.

If air cleaner is receiving outside air from that large open directly above it I still dont get point of vacuum flapper things and why they literally open into a confined foam-space?

Thanks for comeback, FJ,
M

[SD455DJ]

The way I understand the RA heat riser function is the flapper doors on the hood mounted pan have rubber vacuum lines that run to a common ‘T’. From there the single rubber vacuum line runs to one of 2 nipples on the bi-metallic ‘AC’ valve mounted on the RA base pan. Another rubber vacuum line then runs to a vacuum source (usually to the vacuum ‘tree’ at the rear base of the carb). The bi—metallic valve is open when cold allowing engine vacuum to open the 2 flapper doors on the hood pan, thereby allowing heated air from the riser stove to be pulled into the large center chamber with the air filter element, then into the carburetor. Once the bi-metallic valve ‘sees’ enough heat it will close the orifice that supplies vacuum allowing the spring pressure to shut the flapper doors shutting out the heat. This function is to allow faster warm-up and higher warm operating efficiency. I’m open for corrections…

Dennis

[RAIIIJudge]

Your description of components involved is spot on, Dennis, and explanation of their function makes sense, I hadn't thought of that before, thanks.

Guess the 041 RAIV needed extra help on cold morning's judging by the added stove?

[NeighborsComplaint]

A bigger mystery to me is how that valve cover gasket doesn’t leak.

[RAIIIJudge]

Ha, do you really mean how do all four gaskets not leak?

The rockers are Comp Cams Magnum XD 1.6 and don't fit under stock valve covers so each has a spacer. I'm not crazy about them.
I did have car on a lift a few days ago and saw I might have a small leak out the back of driver side valve cover. Thanks for reminding me.

[steve25]

The added heat riser was due to how much faster the Aluminum intake dissipated heat since there was no connection between the intake and the crossover and the engineers still wanted the choke to come off near as fast as a iron intake .

[Kenth]

From the 1969 Pontiac Service Manual:

[SD455DJ]

Actually, the vacuum source is from the nipple screwed into the no. 1 intake manifold runner, not the vacuum tree behind the carb...thanks to Kenth's diagrams!

Dennis