Wastegate mod.....

[avos at cochlear.com.au]

     Simon,
     
     I think that the boost controllers do basically what you want to do, 
     but have one advantage over your system. You may be able to get your 
     system to provide a good boost curve by playing with the comparator 
     settings, but you will be optimising for one set of conditions. ie. 
     you may perform you tweaking with light load (first gear), when boost 
     rises quickly, so you need to start to open the wastegate quicker (at 
     lower boost). This will give you good boost in first gear, but may 
     open the wastegate too early in higher load conditions when boost 
     rises slower (as revs rise slower). The Electronic boost controller 
     can calculate when to start to open the wastegate by looking at the 
     gradient of the boostcurve ie. if it is rising quickly (1st gear, or 
     on-off-on at high revs), open the wastegate earlier. if boost is 
     rising slowly, hold the wastegate closed longer (5th gear up a hill).
     
     Ideally you would want to optimise your settings for the situation 
     where boost rises quickest, as otherwise you could over-shoot to 
     catastrophic boost levels in these conditions if you optimised for 
     slower rising boost conditions. I think that the situation of quickest 
     rising boost is if you have high engine load, and high revs, and then 
     back off (close throttle and reduce boost) and floor it. As boost 
     recovers it should rise really quickly due to already in high revs and 
     high load, so alot of exhaust gas going through the turbo.
     
     One other advantages that electronic boost controllers have is 
     accurate setting of boost, but I don't think this is of concern to you 
     since you don't intend to adjust the boost from the wastegate setting.
     
     Basically I agree that EBCs are over-priced, but they do have 
     advantages. I think they optimise the boost curve better than any 
     other method of boost control, but you can probably do 95% as well for 
     alot cheaper using mods like the one you suggested.
     
     Regards,
     
     Adrian


______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: Wastegate mod.....
Author:  diy_efi at coulomb.eng.ohio-state.edu at INTERNET
Date:    13/10/97 14:07


Hi All
     
>      Unfortunately its not (quite) a perfect world,
     
;-) too true
     
>      and if you do not let 
>      the pressure get to the wastegate a few psi before the set boost 
>      level, you will find that boost may fluctuate (oscillate), 
     
This I know, so just to make sure I have this right your micro device is going 
to 
do the same my compariter device, which is only open the wastegate at the last 
possible moment to achieve a stable boost set point.
     
The 2 promo's of the boost controles I saw weren't very clear all they talked 
about was programmed boost control to achieve more power. All I'm trying to find
     
out is is the boost controlled just doing what I want to do?
     
Cheers
     
Simon
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  Simon Quested (E-mail questeds at lincoln.ac.nz)
  Computer Technician, Silicon Graphics & Windows NT Support 
  Centre for Computing and Biometrics
  LINCOLN UNIVERSITY OF NEW ZEALAND
  Phone (64)(03) 3252811 Ext. 8087
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http://www.lincoln.ac.nz/ccb/techs/simon/default.htm 
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Albert Einstein: "Only two things are infinite, the universe and
human stupidity, and I'm not sure about the former." 
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