Another question, another post - blow off valve and the mysterious vacum lines... - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 01-18-2003, 10:01 PM Thread Starter
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Another question, another post - blow off valve and the mysterious vacum lines...

My HKS blowoff has two vacum ports, both 1/8", One comes out the side, the othe out the top. One ties in with the manifild vacum. I know this because the directions are clear on that. The same manifold vac would tie into the FMU, but I ain't got one. What about the second? Cap it? As usual, thanks.


Mike Smith
1990 LX Coupe 5.0 5 speed w/ 2000 Exploder GT-40 engine, P heads, mystery cam (F cam per previous owner) 3.73, and not much else. In the parts pile - UPR tubular K member, CC plates. Future plans - Megasquirt & On3 turbo system.
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post #2 of 5 Old 01-18-2003, 10:26 PM
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On my Turbonetics one and on most that I have seen, the top one runs to manifold vacuum and the one on the side runs to a boost reference point (like on the side of the compressor housing), but alot of people leave that one open. Turbonetics told me if I still got some air reversion after I let out of the throttle to connect the side port and this would make the valve open faster because when you shut the throttle manifold vacuum goes sky high, which is then in turn pulling through the top connection and the compressor outlet would see a quick spike in boost pressure which would push the diaphragm from the side port. But if you don't use it, you need to leave it open.
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post #3 of 5 Old 01-18-2003, 10:32 PM Thread Starter
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Thanks Mike!
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post #4 of 5 Old 01-18-2003, 10:34 PM
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No problem, glad to help.
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post #5 of 5 Old 01-19-2003, 12:36 PM
 
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I'd say to hook it up like Mike suggest.. With the lower port going to the compressor outlet.. Remember, a blowoff valve is suppose to remain closed, even when the top port is subjected to 18+ inches of vacuum that your motor may see at idle..

In bench testing my HKS blowoff valve, it wouldn't open even with 22 inches of vacuum to the top port..That's about all the vacuum a motor will pull, even with the throttle closed and dragging the car down from high rpms... Now if I had some boost acting on the face of the valve, it might crack open..But when I also put boost pressure to the bottom port, the valve would open wide with authority..
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