Installing my oil catch cans today and noticed intake tubing had another hose connecting to crankcase.

Does anybody know its purpose? Is it also part of the pcv system? (red hose in photo)

 

yes it is

 

So I wonder how much blowby is recirculated through the intake tubes vs the manifold...

I suppose it's possible to run a catch can with two inlets and two outlets? Then both crankcase blowby outlets run through the catch can.

I don't know... It just seems strange to me that everyone has catch cans for the manifold but not for the tube/throttle body. Seems like half a solution.

 

I have stock tubing more or less but from the guys at the 370z boards, catch cans are where its at. They can make a big difference in octane readings while getting a tune. I'm probably missing your point but as far as I know, there's only one option when it comes to catch cans. You either run one to help with crank case pressure or you don't and have blow-by.

 

From what I understand our crankcase blowby is vented via 5 hoses: 3 in intake manifold (one in the rear, two in the front) and one each on left and right in intake tube, right before the throttle bodies.

Our catch cans are designed to catch the blowby from the two hoses in the front going into the manifold. So why is the blowby from the left and right intake tube neglected? Is the blowby there significantly less?

Hope this clarifies my question.