Ron240zxt Posted November 29, 2001 Share Posted November 29, 2001 Hello, would like to throw something out there about my zcar. Here is a few things that ill like to get some of your knowledge on. A: I have a custom intake manifold made for my turbo z car. The intake manifold has airhorns through out the plenum, with a 70mm throttle body attached to it. Here is the delema im running in to. At idle my Vacumm is right at 12 in hg. on my boost gauge and is steady. My map sensor reads -18.5 and is also steady. Why does a electric and manual gauge differ so much? The Next question i have is at the same idle. I have a whistle accuring (supercharger sound) until i have my foot a little more on it and the vacumm is approx above -10.0 the sound goes away. First thought was vacumm leak. i grabed the stethoscope to check around for vacumm leaks, I went around the injectors, throttle body, Head, exhaust manifold and im coming up with nothing. I tryed spraying all the joint parts with wd40 to see if the tone of pitch would change, once again nothing... Im running out of ideas.. (sorry this post is drawn out) Next thing i have to ask is this... Valve adjustment...Any tricks out there or should i just do the conventional way.... I originally adusted the valves cold and when its hot in goes clink clink clink.......Hum time for more work on the car.... Thanks for the advise Ron240zxt Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted November 29, 2001 Share Posted November 29, 2001 Whistle - can you say air going supersonic past the throttle blade? I've got that problem on my Mustang and I've heard it on other cars too. The crack of th eblade is just right and it whistles! The BOV on my RX7 does that too when I have the throttle just right. Vac in the intake but boost in the pipe apparently, whistles like mad! Are you sure both vac guages are right? Are they sourcing vac from the same place? Neither has a crimp in the hose and the hose isn't collapsing? MAP sensor could be wrong, is it's refrence voltage okay? I'll bet that would screw it up if it wasn't receiving the voltage it expected as a supply... Just some ideas - oh and Autometer boost gauges can sometimes be a little off it seems so if that's what you're using that MIGHT be an issue. Let us know what you find! Quote Link to comment Share on other sites More sharing options...
Nigel Posted November 29, 2001 Share Posted November 29, 2001 My 240ZT and my Subaru Legacy Turbo both idle at around 18 in hg according to the mechanical guages I have in each. The reading on the 240ZT is backed up by the reading from the MAP sensor for the SDS computer. So, I'd be inclined to believe the MAP sensor in your car. But a lot depends on your engine setup. I'm running a stock ZXT cam with a '75 280Z intake manifold with a stock ZXT 50mm throttle body. Idle speed is 1000rpm. So, there's a point of reference for you... Nigel '73 240Z Turbo Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 1, 2001 Share Posted December 1, 2001 Okay - just a quick question - what MAP sensor do you have that actually shows vacuum readings? Is this some sort of gauge or are you using this with a FI system of some sort? Usually MAP (Manifold Absolute Pressure) sensors don't show vacuum, since that's a relative reading, not an absolute reading. Vacuum is pressure referenced to atmospheric pressure. So, if you have some sort of MAP sensor setup that reads vacuum, it would need to be calibrated to the current atmospheric pressure in order to work properly. Does it read zero vacuum when the engine isn't running? Quote Link to comment Share on other sites More sharing options...
Ron240zxt Posted December 3, 2001 Author Share Posted December 3, 2001 Sorry Tim, I confused myself on that one. You are right. Thanks ROn Quote Link to comment Share on other sites More sharing options...
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