Boost target issue?

[Evo_Jay]

So I'm tuning an EVO with a Link ECU. Tuned the boost in open loop first, had it holding 20psi just fine. Got a good wastegate duty map from that.

Next moved to closed loop boost control and I don't know if my settings are wrong (Set them up according to the instructions) but the P&I is pulling a bunch of wastegate duty, even though I'm below boost target.

Any idea why?

[Vaughan]

Attach your log and tune please

[Evo_Jay]

okay. here you go.

Mitsubishi Evo 5 (Tim) V8b.pclxPC Datalog - 2023-05-2 8;18;26 pm (B).llgx

[Vaughan]

Boost target table values are in MAP not MGP and so where you have a target of 20kPa that is absolute, I suspect at that point you are wanting 120kPa (20kPa over Barometric pressure at sea level)

[Evo_Jay]

36 minutes ago, Vaughan said:

Boost target table values are in MAP not MGP and so where you have a target of 20kPa that is absolute, I suspect at that point you are wanting 120kPa (20kPa over Barometric pressure at sea level)

I have it targeting 20psi, not 20KPA. Since I have everything scaled in PSI, a boost target of 20psi should be 34.7 PSi absolute. And even the graphing shows this, as my target psi is higher then the actual psi.

I don't want anything in KPA. Where I'm from, we use PSI, not KPA.

Why is there no ability to change the pressure scaling for the boost table? And are you saying the boost table is absolute psi, and if I want to target 20psi, I should put 34.7 psi in the table?

[Vaughan]

1 hour ago, Evo_Jay said:

I don't want anything in KPA. Where I'm from, we use PSI, not KPA.

If you want things displayed in psi use the imperial display setup by pressing the 'U' key, which units are used in each mode can be specified in Options -> Units -> Options. All calculations in the ECU are done in SI units.

1 hour ago, Evo_Jay said:

I have it targeting 20psi, not 20KPA

In the supplied basemap it absolutely is targeting 20kPa at 1500RPM/30kPa MAP or 2.9psi at 1500rpm/30%TPS. I was looking at it in kPa and took the first value I saw as my example not the highest boost value which might explain the confusion between my 20kPa and your 20psi.

1 hour ago, Evo_Jay said:

Why is there no ability to change the pressure scaling for the boost table? And are you saying the boost table is absolute psi, and if I want to target 20psi, I should put 34.7 psi in the table?

The reason for using absolute pressure is that if you travel to a lower or higher altitude you want the amount of air being shoved into the motor to be the same. Yes if you want 20psi of boost on top of atmospheric pressure and assuming your atmospheric pressure is 14.7psi then you would target 34.7psi.

[Evo_Jay]

15 hours ago, Vaughan said:

If you want things displayed in psi use the imperial display setup by pressing the 'U' key, which units are used in each mode can be specified in Options -> Units -> Options. All calculations in the ECU are done in SI units.

I have mine setup for imperial units. You don’t. That’s why it’s in kpa when you look at it. 

In the supplied basemap it absolutely is targeting 20kPa at 1500RPM/30kPa MAP or 2.9psi at 1500rpm/30%TPS. I was looking at it in kPa and took the first value I saw as my example not the highest boost value which might explain the confusion between my 20kPa and your 20psi.

what I was saying is I was not trying to target 20kpa. I was trying to target 20 psi. Or 34.7 psi absolute. But links unit labels suck like I explained below. 

15 hours ago, Vaughan said:

The reason for using absolute pressure is that if you travel to a lower or higher altitude you want the amount of air being shoved into the motor to be the same. Yes if you want 20psi of boost on top of atmospheric pressure and assuming your atmospheric pressure is 14.7psi then you would target 34.7psi.

 

the confusion is that link doesn’t label their units correctly. “Psi” means relative psi. “Psia” means absolute psi. They need to put “psia”, not “psi” if they want people to know it’s absolute psi. Even in all their instructions, they don’t mention that the table is absolute psi  

And I totally understand absolute pressure. You don’t have to explain it. Been tuning cars that use absolute pressure for about 20 years now.  It’s just that link didn’t have it labeled as absolute pressure. They had it labeled as relative pressure. 

[Vaughan]

6 hours ago, Evo_Jay said:

Even in all their instructions, they don’t mention that the table is absolute psi

I have added notes in a couple parts of the help manual to clarify that the target tables are in absolute pressure not gauge pressure.

[Adamw]

Note for closed loop boost control, even once you update the target table values to absolute pressure, the smallest value in your target table shouldn't be any smaller than the lowest "spring pressure" the turbo system can provide.  The stages switch based on how far away from target you are so with values below spring pressure it there it is going to switch into stage 3 before the ecu is even providing any control.  Stage 1 is open loop, stage 2 is proportional and derivative control, stage 3 is proportional and integral, so it is important to have these switch at a suitable point in the control curve.