grainy;

...very good info from all, but I don't think I saw anyone mention that the crankcase gases are mixed into that (prewarming) chamber which the intake mixtures are routed through under part throttle (under full throttle, the seconcary throttles were opened and the mixtures ran directly into the head - to call it a rudimentary form of variable-tuned intake is not incorrect, Al).

But this mixing with oil vapor/droplet containing crankcase gases is what I believe causes the problem which this manifold is known for: Poor and/or unrepeatable idling.

From my observations, the crankcase gases cause deposits in that chamber when the oil components hit the chamber surface during hotsoak after shutting engine off (naturally, the higher the mileage on the engine, the more blowby, the more deposits), these build up and eventually catch fuel dropplets and can even cause them to puddle...after that, there's now way to get any kind of repeatable idle control...and we haven't even mentioned any additional false air getting past the secondary throttles...idle, what idle?

So the intake side is kinda hopeless, but the exhaust side is possibly the highest flowing 4 into 2 casting from the factory! That's why it's not unheard of to separate the two...replacing the intake side with a <'66 alu unit, and leaving the stock exhaust...it's not a header, but it won't rust through in 10 years either! I works great, I've done it too!

Cheers