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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 03-18-2014, 11:25 AM   #1
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Boost creeping!!

Well here's the scenario. I have a rb25 Freddy intake, tomei mild cams, cx racing top mount manifold with a bb gt35r. Wg dump tube is a screamer pipe. Hks bov and Tial 38mm with a 6 lb spring. The wg is vented to atmosphere on top port and bottom port is connected to a nipple on the intake housing on the turbo. As I drive the boost creeps slowly up to about 22 psi. So I pulled the wg out to check for leaks. Only a small leak around the valve which is said to be normal. When connected to a Manuel bike pump the wg opens fine at around 6 psi. Also checked the wg on the car with the car running, again connected the pump to the wg (wile car is running) and you can clearly hear the valve open. When I checked the port on the compressor housing for vaccum it's around -5 to 0 psi at idle. When at the manifold my aem gauge says I'm -20 psi at idle. Any ideas?!?
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Old 03-18-2014, 11:58 AM   #2
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You shouldn't see any vacuum at the turbo unless you have run a vacuum source over there. Right off the turbo you're going to see boost pressure only. If you see -20in/hg on your AEM, that's because your MAP or vacuum source is reading that directly off the intake manifold after the throttle body.
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Old 03-18-2014, 12:10 PM   #3
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Okay so no vaccum before tb is normal. Yes the aem is connected to manifold after tb

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Old 03-18-2014, 12:11 PM   #4
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check your vac lines for leaks. The wg line might be leaking when you get into boost.

..and be careful. 22psi is a hell of a creep on a 6 psi spring
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Old 03-18-2014, 12:35 PM   #5
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OP, please take apicture of wher the WG connects to the turbo houseing, I feel, for some reason, the wastegate may not be routed to a boost only source.
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