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Old 07-13-2013, 08:35 PM   #1
Scooby Newbie
Member#: 82786
Join Date: Mar 2005
Chapter/Region: TXIC
Location: Plano, TX
2004 WRX

Question Best practices: WGDC table or actuator arm for target boost

I was looking for an opinion from tuners far more experienced than I. If a tune is not quite reaching target boost (1-1.5psi short). Is it a better practice to modify the Wastegate Duty settings or make a small adjustment to the actuator arm (.5-1 turn shorter)?

I've read that you don't want to run a duty cycle too high due to "wear" on the solenoid but other than Cobb's whitepaper mentioning "keep it below 95%", I've not found reference to what too high really is. The stock duty cycle for my 04 WRX starts at 96.1 but tapers down as the RPM and Throttle combinations rise. So is the 95% rule for any table settings or just the lower RPM and Throttle entries?

Alternatively, I've read mixed information about adjusting the wastegate arm. Some say it's a valid and correct way to adjust issues with target boost while others vehemently state that you don't address target boost issues with an arm adjustment.

In my recent tuning (due to replacing my stock TD04 with a like unit) I've been doing some changes and logging. (Lesson learned that you have to use the old actuator between 2.0 and 2.5 turbos.) I'd run into some boost spikes but then compensated for them to the point where it's now just shy of reaching target boost, around an average of 1psi over the rev range. For that final tweak, would modifying the wastegate duty table be better or just do a half turn on the wastegate arm. I think both might give similar results but I'm not familiar with the best practice. Does it matter and are the advantages/disadvantages to each? There does not seem to be much, if any pre-load on the wastegate at this time.

Currently logs show a wastegate duty cycle in the 70s range in the 2500-5500 RPM and then dropping incrementally lower as revs rise. Below 2500 its in the 80-98 range. Is there room to raise this higher in that 2500-5500 range without premature wear to the equipment Cobb references? Is 1 psi within variances and I should just leave it as-is?

I can post a log if needed for a better picture. Not promising all needed fields would be represented though.

Thanks for the time.
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rt4me is offline   Reply With Quote
Old 07-13-2013, 09:22 PM   #2
Scooby Specialist
Member#: 137405
Join Date: Jan 2007
Chapter/Region: MAIC
Location: Baltimore
2011 WRX


id say get an aftermarket ebcs and tune the wgdc's.
bluemax189 is offline   Reply With Quote
Old 07-14-2013, 11:35 AM   #3
NASIOC Supporter
Member#: 235338
Join Date: Jan 2010
Chapter/Region: South East
Location: Georgia
2002 Faggin Wagon


There is a correct way to adjust the arm on the wastegate actuator and I don't have the picture/explanation on this computer.... Remove the "e" clip and slip the adjustment loop off the wastegate flapper door stud at the back of the turbo. With the flapper door completely shut, the wastegare arm should have to be pulled over the stud the distance of half the diameter of the hole in the adjustment arm. After this is done, tune WGDC as you wish. I preffer MBC's to 3-ports but either one is better than the factory solenoid.

If you want the picture/diagram I have created, email me and I will get it to you.

Steve @ Pullz-On Tuning
dux10 is offline   Reply With Quote
Old 07-14-2013, 12:59 PM   #4
Scooby Newbie
Member#: 82786
Join Date: Mar 2005
Chapter/Region: TXIC
Location: Plano, TX
2004 WRX


Thanks for the info. I'm familiar with the wastegate arm adjustment procedure but wasn't sure if there should be any "pre-load" (pull the arm over the stud). Mine wasn't. I'll make an adjustment and then re-log.

I've got very few mods (gutted stock uppipe, cat back, silicone hoses...that's it.) and have a tweaked "Stage1" map with what I think are fairly conservative settings. Peak target boost is 15. I didn't think with the light mods I have that I would need an aftermarket BC. I'm just tuning for safe, smooth drivability, not peak power.

I'll look into the aftermarket BC, adjust the wastegate arm to take out the slop and then log. If that doesn't work then I'll investigate further duty cycle changes.

I'm still wondering what is too much on the WGDC. Thanks again for the advice and keep it coming.
rt4me is offline   Reply With Quote
Old 07-14-2013, 09:27 PM   #5
Scooby Newbie
Member#: 280926
Join Date: Apr 2011

+1 to pre-loading the wastegate arm.

The stock boost control system is adequate for your needs. I get the feeling that many of the advocates for MBCs and EBCSs began using them in situations when they were unable to adjust the ECU WGDC tables and just continue to use them now because they understand them better. Plus they definitely make it easier to adjust the boost. However they are not a requirement to make more boost.
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