boost sag question - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 02-03-2011, 07:54 PM   #1
Junior Member
Thread Starter
iTrader: (6)
 
Join Date: Mar 2009
Location: Los Gatos, CA
Posts: 120
Total Cats: 0
Default boost sag question

I have a boost sag problem. Boost is stable up to ~5500rpm. Then it steadily drops from ~12psi to ~9psi from 5500rpm to redline.

Name:  saggingnuts.jpg
Views: 1
Size:  46.5 KB

Hallman MBC is sourced just prior to TB.
Full 3 exhaust with high flow cat
Stock intake
Bell cast manifold and DP
Garrett 2554 with 6psi actuator

Is this turbo just too small to keep boost up at the higher rpms?
Or is the wastegate being pushed open?
Do I need a helper spring or could it be something else?

Thanks
Slayer is offline   Reply With Quote
Old 02-03-2011, 08:02 PM   #2
Senior Member
iTrader: (2)
 
Join Date: Aug 2005
Location: Granbury, TX
Posts: 567
Total Cats: 1
Default

I would think that your wastegate is the issue, and either a stronger one or helper spring would be needed.

Not that this anything to do with it, but your injector DC sure does get high?
greenday3437 is offline   Reply With Quote
Old 02-03-2011, 09:10 PM   #3
Junior Member
Thread Starter
iTrader: (6)
 
Join Date: Mar 2009
Location: Los Gatos, CA
Posts: 120
Total Cats: 0
Default

Quote:
Originally Posted by greenday3437 View Post
Not that this anything to do with it, but your injector DC sure does get high?
yeah, and it was way rich at high RPM in this log. duty went down as we leaned out the high rpm cells in subsequent pulls. I used this pull because it most clearly depicts my boost sag condition.
Slayer is offline   Reply With Quote
Old 02-04-2011, 02:43 PM   #4
Elite Member
iTrader: (2)
 
Join Date: Jun 2006
Location: ABQ, NM
Posts: 1,850
Total Cats: -8
Default

Throw a new wastegate actuator at it. Something in the 10psi range should help.
BenR is offline   Reply With Quote
Old 02-05-2011, 06:06 PM   #5
Senior Member
iTrader: (2)
 
Join Date: Aug 2005
Location: Granbury, TX
Posts: 567
Total Cats: 1
Default

Yes.. I'm sure you know this already, but the ideal setup is to have a wastegate that holds closest to your target boost level. Then if you need a few more psi then use the boost controller to up it a few psi.

Not that people really do that, but most likely that's your problem.
greenday3437 is offline   Reply With Quote
Old 02-05-2011, 08:21 PM   #6
Junior Member
Thread Starter
iTrader: (6)
 
Join Date: Mar 2009
Location: Los Gatos, CA
Posts: 120
Total Cats: 0
Default

Quote:
Originally Posted by greenday3437 View Post
Yes.. I'm sure you know this already, but the ideal setup is to have a wastegate that holds closest to your target boost level.
Nope, didn't know that. But it makes sense. Thanks.

Would a helper spring effectively be the same as a new higher rate wastegate actuator, or no?
Slayer is offline   Reply With Quote
Old 02-06-2011, 01:21 PM   #7
Senior Member
iTrader: (2)
 
Join Date: Aug 2005
Location: Granbury, TX
Posts: 567
Total Cats: 1
Default

Quote:
Originally Posted by Slayer View Post
Nope, didn't know that. But it makes sense. Thanks.

Would a helper spring effectively be the same as a new higher rate wastegate actuator, or no?
It may help, or even hide your problem, but it's somewhat a band-aid.

It's a cheap way to fix the problem, but of course it's not the "most correct" way to do it.
greenday3437 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 Yesterday 09:00 PM
LucaCarMods's Boosted Dutch Miata Build! LucaCarMods Build Threads 11 02-14-2016 07:13 AM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM
Bad head gasket or ? shooterschmidty Engine Performance 8 09-30-2015 11:28 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 03:40 AM.