Control would be much simpler all around if the WG had an electric-powered 
actuator.  The boost-powered version requires compensation for 
continuously-changing boost pressure and it can't do anything at all when boost 
is too low.  
  ----- Original Message ----- 
  From: Jason C 
  To: [email protected] 
  Sent: Monday, June 23, 2008 6:49 PM
  Subject: turbos and fuel economy


  I know some of you guys don't surf the miataforum so here.

  This article shows the BSFC plots of an engine before and after turbo:
  
http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/image/Final_30.gif

  Here's the specific graph:
  
http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/image/Final_30.gif

  On a slightly different topic, the BMW 335i offers very good MPG for the 
car's power and weight.  One strategy they have is that the wastegate is open 
during cruise.  This would presumably reduce backpressure and thus reduce 
"blowdown" losses during the exhaust stroke.

  I've always advocated using a large-diameter, low-PSI wastegate can, and 
using TPS-controlled EBC, for driveability.  One downside is that tuning boost 
control will be tricker.





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