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JRSC loses boost toward redline

 
Old 10-19-2018, 09:18 AM
  #21  
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Yes, I counted 19 teeth between timing marks.
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Old 10-19-2018, 09:23 AM
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You can have 19 and still be off. Confirm cam/crank timing at TDC.

edited
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Old 10-19-2018, 09:27 AM
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I'll look into that as it seems like the best theory so far.
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Old 10-19-2018, 12:49 PM
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Ted, are you saying that the cams may be out of alignment with the crank? I checked the crank and cam timing marks when I had it apart and they all line up at tdc.
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Old 10-19-2018, 02:22 PM
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Yeah, it can be pretty easy to get a cam gear off by 1 tooth. A screenshot with WOT starting earlier in the RPM band might be helpful too.
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Old 10-21-2018, 02:21 PM
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Here's a screenshot with wider RPM band WOT from 2700 to 6200. The logs look like this every time. Start at about 5 psi, up to nearly 8 midrange, then down to 5.5 up top.


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Old 10-21-2018, 02:58 PM
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What is your VE doing there?
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Old 10-21-2018, 03:22 PM
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Here you go. Added VE to the top plot in yellow


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Old 10-21-2018, 04:25 PM
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Yeah, see how it dips? Miata motors are not supposed to do that. That should be the torque peak range. Your engine is consuming less air there than it should, which is why you have higher manifold pressure. Basically, manifold pressure is equal to the supercharger output volume divided by the engine intake volume. When the engine intake volume decreases, the manifold pressure increases. What is your idle map reading?

edit: and idle RPM
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Old 10-21-2018, 04:52 PM
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I idle at 900 rpm and 20-21 in hg
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Old 10-21-2018, 05:21 PM
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My guess is that your intake cam is retarded by 1 tooth.
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Old 10-21-2018, 05:23 PM
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Or the TBelt slack wasn't taken out properly.
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Old 10-21-2018, 05:42 PM
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Thanks for the help. I'll definitely look into that. So what does the idle value tell you? I'm curious how that plays into this.
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Old 10-21-2018, 06:16 PM
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Exhaust cam off can really show up in idle vac.
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