Notices
Supercharger Discussion For all you misguided souls.

JRSC loses boost toward redline

Thread Tools
 
Search this Thread
 
Old Oct 19, 2018 | 09:18 AM
  #21  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

Yes, I counted 19 teeth between timing marks.
Old Oct 19, 2018 | 09:23 AM
  #22  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

You can have 19 and still be off. Confirm cam/crank timing at TDC.

edited
Old Oct 19, 2018 | 09:27 AM
  #23  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

I'll look into that as it seems like the best theory so far.
Old Oct 19, 2018 | 12:49 PM
  #24  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

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.
Old Oct 19, 2018 | 02:22 PM
  #25  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

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.
Old Oct 21, 2018 | 02:21 PM
  #26  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

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.


Old Oct 21, 2018 | 02:58 PM
  #27  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

What is your VE doing there?
Old Oct 21, 2018 | 03:22 PM
  #28  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

Here you go. Added VE to the top plot in yellow


Old Oct 21, 2018 | 04:25 PM
  #29  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

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
Old Oct 21, 2018 | 04:52 PM
  #30  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

I idle at 900 rpm and 20-21 in hg
Old Oct 21, 2018 | 05:21 PM
  #31  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

My guess is that your intake cam is retarded by 1 tooth.
Old Oct 21, 2018 | 05:23 PM
  #32  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

Or the TBelt slack wasn't taken out properly.
Old Oct 21, 2018 | 05:42 PM
  #33  
cyclopat's Avatar
Thread Starter
Junior Member
 
Joined: May 2017
Posts: 59
Total Cats: 0
Default

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.
Old Oct 21, 2018 | 06:16 PM
  #34  
Ted75zcar's Avatar
Tweaking Enginerd
iTrader: (2)
 
Joined: Mar 2013
Posts: 1,873
Total Cats: 383
From: Boulder, CO
Default

Exhaust cam off can really show up in idle vac.
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
fatalist
Supercharger Discussion
12
Oct 31, 2016 11:33 AM
terrorik
Supercharger Discussion
40
Mar 25, 2016 01:17 PM
Sentic
DIY Turbo Discussion
7
Oct 14, 2013 04:37 PM
Kuksi
Engine Performance
2
Sep 12, 2011 05:40 PM
yanik
Engine Performance
12
Jun 10, 2010 08:58 AM




All times are GMT -4. The time now is 08:16 AM.