Boost tapering at high RPM? - Subaru WRX Forum
 
LinkBack Thread Tools Display Modes
#1 Old 12-31-1969, 07:00 PM
Moderator
 
Join Date: Nov 2001
Posts: 311
Images: 3
Gerlando is an unknown
I've heard that boost starts to cut back at higher RPMs and I never really noticed this effect, but today I decided to see what people were talking about. I was surprised to see that at about 6000 RPM, boost dropped dramatically from 14psi to about 7psi! Is this normal? I'm thinking my catless uppipe and 3" exhaust might have something to do with it,.. or I have an exhaust leak,... or its normal,..



Anyone out there notice the same thing
Gerlando is offline  
Sponsored Links
Advertisement
 
#2 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
mikeWRX's Avatar
 
Join Date: Nov 2001
Posts: 252
Images: 5
mikeWRX is an unknown
The Stock ECU and FBC is programmed to taper boost at high RPM's. If your using a MBC then it probably has to do with the TD04 turbo being out of it's efficiency range, or you have an exhaust leak.
mikeWRX is offline  
#3 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
HRTATAK's Avatar
 
Join Date: Nov 2001
Location: Mississippi
Posts: 194
Images: 9
HRTATAK is an unknown
Hey Mike...are you saying that a MBC wouldn't help....because I was thinking about buying one because it's so much cheaper than an electronic one...
HRTATAK is offline  
#4 Old 12-31-1969, 07:00 PM
Moderator
 
Join Date: Nov 2001
Posts: 311
Images: 3
Gerlando is an unknown
An MBC DOES help. I had one on my WRX and set it to 13psi and got it just about anytime I wanted. I threw a CEL so I took it off and never put it back on.



I later found out that having full boost at partial throttle isn't a good thing for EGTs so I'm not putting it back on without an EGT gauge.
Gerlando is offline  
#5 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
HRTATAK's Avatar
 
Join Date: Nov 2001
Location: Mississippi
Posts: 194
Images: 9
HRTATAK is an unknown
hey G...does the turbo hold max boost until redline with the MBC? The CEL won't bother me that much. If it does...I'll take the bulb out of the dash...

[ This message was edited by: HRTATAK on 2001-12-11 21:27 ]
HRTATAK is offline  
#6 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
Join Date: Nov 2001
Posts: 9
BugEyed is an unknown
Beware, the stock ECU retards the ignition and richens up the fuelling if you run high boost and revs. You will still get some benefit, but not as much as you hoped for.



More importantly, beware the high EGTs that Gerlando mentioned above if you have full boost on part throttle. I suggest that if you use an MBC then you should pick one that allows you to avoid this problem (such as the TurboXS one).



Duncan
BugEyed is offline  
#7 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
mikeWRX's Avatar
 
Join Date: Nov 2001
Posts: 252
Images: 5
mikeWRX is an unknown
Oh yeah, a MBC will definitely help. Just get one that combines the ball and spring design with the bleed off valve type. That way you can set the ball and spring to a lower boost for part throttle and set the bleed off one to high boost for full throttle.



Here is a link that shows you how to make one of these type of MBC's.



Low boost/high boost boost controller



Gerlando, you already have the first part of this, all you have to do is add the needle valve section after the ball and spring MBC and set the ball and spring boost to around 7psi for partial throttle position.
mikeWRX is offline  
#8 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
HRTATAK's Avatar
 
Join Date: Nov 2001
Location: Mississippi
Posts: 194
Images: 9
HRTATAK is an unknown
Do you need a needle valve after the ball and spring MBC....or just use a restricter like some of the others.....

[ This message was edited by: HRTATAK on 2001-12-14 14:13 ]
HRTATAK is offline  
#9 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
mikeWRX's Avatar
 
Join Date: Nov 2001
Posts: 252
Images: 5
mikeWRX is an unknown
I suppose you could just use a restrictor. The needle valve just adds a lot more adjustment to the amount of restriction. (Thereby offering more adjustment to the max boostlevel.)
mikeWRX is offline  
#10 Old 12-31-1969, 07:00 PM
WRXtuners Member
 
HRTATAK's Avatar
 
Join Date: Nov 2001
Location: Mississippi
Posts: 194
Images: 9
HRTATAK is an unknown
Thanx Mike....this is a good MBC for less that $50....It's just going to take some trial and error to adjust...but saving money is always a good thing...
HRTATAK is offline  
Reply


Currently Active Users Viewing This Thread: 3 (0 members and 3 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On