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Spring pressure

Boost Control

Discussion and questions related to the course Boost Control

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Hey Guys,

Was just having a look through my wastegate duty cycle tables and noticed that below 200kpa my duty cycle is set to zero. Is this set up because my wastegate spring is 100kpa - and would hold itself closed at those pressures anyway? Will adjusting the duty cycle near the pressure where the wastegate starts to crack open would result in more preload or just be better practice?


Do you have a datalog of you doing a WOT pull, showing actual duty cycle and boost pressure in use?

Unable to get a good example of a pull at this stage, could this question just be asked generally speaking?

Would altering my duty cycle table around the crack pressure of the wastegate spring affect the pre-load in some way? I'm interested in what others have experienced when doing this is there is anything to be gained.

I currently have an EFR7670 on an RB26 and I feel as though the preload on the wastegate has been reduced too much - just seeing if there's a method in the boost control I can use before actually tightening the actuator arm screw.

Without knowing more about your setup it's a little hard to give a solid answer. If your table values are zero and you're ending up at or above this boost level then it's safe to say your base spring pressure is higher. There's nothing wrong with doing this but raising the duty cycle in the area below your boost target can offer a small improvement in spool.

Managed to get 2 logs of some testing I did today, the "high boost" log is one where introduced some duty leading up to 200kpa to see if that made a difference.

The second one "no duty" is where I used a secondary boost map with no duty at all to see what the spring would work with. This did feel strange as the pressure fluctuated more and I could definitely feel the boost waver.

I'd be interested to hear what you think about these logs, here's a picture of the turbo setup.

Attached Files

Ok there are a few problems here. First of all it looks like your high boost log is using closed loop control yet (I'm guessing) at this point you don't have your base duty cycle table properly tuned. this is why you're seeing the boost drop quickly and then bounce back up. As I've posted elsewhere, the closed loop boost control system in the G4+ currently is ineffective. I'd highly recommend you operate in open loop mode and use the 'passive closed loop' technique described in the course.

For your low boost log the duty cycle is constantly jumping from 90% to around 30% which is why the boost is unstable. Disable the closed loop control and follow the tuning steps in the course and you'll get accurate and stable control.

Thanks for the advice Andre - the more I look at the logs I start to see the holes in where this should be better controlled.

Just in regards to the set up of your "passive" closed loop control (particularly with the RX-7 on your webinar) you set up open loop broadly and then changed your table axis to better focus on control around the target, does the ECU remember the values you set before the table was re-initialised? I have a feeling this is a silly question but thought it'd be best to ask.

The easiest way to do this is to start with a simple 2D table relative to rpm. Once you have good control at your target you can enable the MAP axis and then just copy your single tuned row through the rest of the table. Once you've done that you can make the adjustments above and below your target.