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Link G4 boost control

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Hi guys,

i am having problem where I can’t get a flat boost curve on my twin turbo RB26

No matter how many times i take it for a drive and adjust the duty cycle to try and get it as flat as possible. The next time i drive it, it’s oscillating again. It spikes and drops way below boost target constantly. I feel like I’m fighting a losing battle

Any ideas what could be causing this?


Attach a log and your tune.

Tune and log attached

Attached Files
  • Lee-r32-gtr-tune.pclr
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  • Log-2020-03-22-34303-pm-1st-tune-and-boost-control-adjustment.llg
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Ok, the log is no good since you dont have any of the boost control parameters logged, I suggest you use PC Logging next time and hit the "Add all" button in the logging set up screen so it will just record everything.

But from just a general browse through your set-up I suspect the main problem is because your system needs too much duty cycle to achieve you target boost - the MAC valves will typically be wide open somewhere 75-85%DC and become very erratic around that point where they top out. You have 77-82% in your feed forward table so closed loop is going to have no chance of making a quick correction when starting from there. So you need to get your DC operating down in a region where the valve behaves more linear and repeatable (30-70% is a good place to be). This will likely require some strategically placed restrictors in the plumbing.

Ah ok that makes sense, where do you place these restrictors? Never had to use any before. This is the first time i have had boost control issues like this

Info below from the Link help file. Note, you dont need both the yellow restrictors, just whichever end is the easiest. Often a MIG welder tip is a good ready made option.

So could I basically put the stock restrictor back in? As the rb26 had a restrictor for the stock boost solenoid which i removed when fitting the mac

It will be well worth a try. Too many variables to guess, but basically what you are trying to do is restrict the flow of the pressure source to level that the mac valve can adequately bypass with a moderate duty cycle. If you restrict too much your wastegate will be slow to fill and you will get overshoot, if you dont have enough restriction the boost valve duty will be too high.

Ok thanks Adam. Will give it a go

I am still confused as to how it requires so much duty cycle when the target boost is only 1.3bar. I thought normally you would need to restrict for bigger boost levels. Turbos still have room to be pushed too

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