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Upper intake vaccum/PCV routing

727 views 7 replies 3 participants last post by  dmo 
#1 ·
Curious if anyone knows for certain why the PCV was routed to the side of the plenum as well as the bottom at the vacuum distribution on the 86-93 intake. I'm assuming it was to provide as much PCV evacuation as possible by using two ports. The Track Heat intake is set up the same way as the OE intake was. I called Trick Flow and got "I have absolutely no idea why......." followed by awkward silence, indicating the conversation was over.

I'm in the process of chaning a few things around and wanted to be sure.
 
#3 ·
I've been thinking about this entire system far too much for the last few weeks haha.

I am obviously missing something. The pcv goes to a tee on the side of the intake. The other side of the tee goes to the bottom of the upper intake. I was trying to understand if that was to increase flow of the pcv (two ports to draft from), or because of some flow characteristic where the center of the plenum pulls better at a certain rpm range and the corner at another. Or.....????

I've not seen a cutaway view of an upper intake, so im not certain how the positions coincide with the runners or how that effects the system.
 
#5 ·
On the Cobra and GT40 intakes, the main vacuum source for the PCV is the center port on the upper intake. The port on the end of the upper plenum (closest to the master cylinder when installed) should have a 90* fitting with an approximate 0.125" hole drilled in it. The plenum port/fitting is there to offer a drain for any condensation or oil that accumulates in the upper plenum. The second vacuum source with the restriction is figured into the design of the PCV system.
 
#6 ·
The way you described that setup sounded wrong, but I think I follow how you were describing it. It sounded like the plenum port just had a 90 to drain oil and the pcv went to the central port. That would be draining up hill haha. I pulled
a stock intake and cobra intake out to look. So you are saying the tee has a small orifice to drain oil and that is the primary purpose of that port? Ive not stripped one of these down in forever so I didn't recall the tee having a small hole.

I had thought the Cobra had it on the side, but there it is on the bottom.

I guess Trick Flow didn't get the memo with theirs being on the side, or they were only concerned with draining oil once it was pooled up more than 1/4".
 

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#7 ·
---snip--- So you are saying the tee has a small orifice to drain oil and that is the primary purpose of that port? ---snip---
Yes. I didn't know the fitting on the plenum had an orifice until I engaged in a conversation with an engineer who worked for Roush back in the Windsor days. Condensation in the plenum was found to be an issue in cold weather testing and we all know about the PCV dragging in oil. The restricted plenum port was the solution.
 
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