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Boost control strategy


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Hi All,

I'm trying to find a way to stabalise boost with the G4 

Currently using a Mac 3 port, with open loop mode, RPM activation 1500, 100 kpa.

Table is set up with RPM and MGP.

I know there is a dead zone with the solenoid, so <10% doesn't really do anything. Wastegate pressure is 7psi, target 11psi max.

Duty cycle for the solenoid set to 27% from 1500 RPM, the plan was to bleed pressure from the wastegate for slightly better spool, but pressure does spike, it will peak at around 175kpa, or 75kpa positive boost, so a little short of 11, but as RPM climbs boost reduces. To achieve 11 I'd need to reduce spool / lower RPM and KPA numbers, then perhaps increase at the top end, if I go to 29% at lower range, KPA will spike too high (11.5psi).

I'm setting higher RPM, and increasing the duty cycle as MGP reduces at higher RPM, but my concern is that if I was to full throttle at higher RPM, that extra duty cycle will result in a larger spike.

I have MAP limit set to 190 hence 11.6ps a spike on boost will set off the soft cut.

I don't feel like open loop will achieve a stable boost, and that I may need to reduce duty cycle in spool up RPM and lower KPA cells and increase higher up pressure and RPM at the high end.

Is it possible to achieve stable boost with open loop and a 3 port? If so, any advice on a better method of tweaking the table? i also notice some people use RPM rather than pressure.











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Thanks Adam, sorry have been crazy busy re assembling the charge cooler system and building heat shields.

I’m on my mobile right now but will message you the map soon.

That’s a good point, i’ll check at wastegate pressure but can only do that when the car is back together.



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It's set to open loop, it's a MAC 3 port, activation 1500 rpm, 100kpa MAP,  20hz.

I just checked some old logs at wastegate pressure, I guess it is stable, average 60kpa, fluctuates here and there up or down by 1 kpa, so 59 then 60 then 61 then 60, a couple of peaks at 62.

With my setting, it will peak at around 76 on boost when it spools up, and will vary with lows of 69 sometimes less, it won't hold a steady 76ish. I'm looking at a target of 11psi, so close as I can get to 76kpa solid. I am working on the charge cooler system, and need to know that I can maintain steady 11psi with no pipes blowing off etc, and control IAT at a ramp run with stable pressure as close to 11 psi as I can before the final mapping.

I did assume perhaps the wastegate duty cycle is too high low down, but it's a gt28 on a small-ish engine (1.8) so i'd like less pressure seen at the wastegate early to allow a bigger hit when spooling. The setup somehow seems to allow the boost to spike, then it settles down further on. This is a tweaked one, it was around 27 across the board to start, then dropping to 26, then 21, then 0 in case of spikes. I'm going to try and move the duty cycle up to 28 higher up the RPM and in the lower cells to see if it will bring the boost back up but not sure. I need to try and get 11ish PSI fairly stable then I can dial in the settings.

I've got the softcut set at 80kpa, so not much room for a spike, but I don't want to spike as high as 11.6psi anyway.

You can see below it peaks at desired 76, but then is a little unstable eventually dropping 1 kpa at a time until it hits 69, then fluctuates 1 or up or down, quite a big difference, I only get desired boost at spike when first spooling on full throttle.


Thanks for your help!







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