I would like suggestions or feedback for an idea I have as to how to properly tune an engine with a variable geometry turbo using speed density. Since the newer ms3 alpha code allows a simple direct interface with the he351vgt factory controller I think more people may be interested in experimenting with it now. One of the main advantages of megasquirt has always been based on speed density tuning. The problem is the range of change with the turbine's effective A/R is pretty huge and the relative change in exhaust back pressure it creates. The problem with that being the obvious unaccounted for affect it will have on engine VE and obviously the SD tune.
My plan is to run a pressure sensor in the exhaust before the turbo. Then use a blend curve between 2 SD maps. One tuned with the vanes full open and one full closed. Then use the back pressure sensor as the input for the blend % between the 2 maps.
Is this a sound theory? Any obvious problems or reasons it would not work?
SD tune with variable geometry turbo
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timiacobucci
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elutionsdesign
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Re: SD tune with variable geometry turbo
I see no reason why it wouldn't work, I would use a short length of stainless steel tubing (1/16" OD) between the TIP (turbine inlet pressure) port and the sensor itself to dissipate excess heat. I have that exact setup on one of my cars, without the variable geometry turbine, I was just curious about TIP.
At first thought I would want to believe that a variable geometry turbine actually evens TIP out across the range of compressor pressure instead of spiking when the A/R is too small or never really building above compressor pressure when the A/R is large.
At first thought I would want to believe that a variable geometry turbine actually evens TIP out across the range of compressor pressure instead of spiking when the A/R is too small or never really building above compressor pressure when the A/R is large.
Graduate of EFI University.
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
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timiacobucci
- MS/Extra Newbie
- Posts: 8
- Joined: Mon Jun 23, 2014 3:01 pm
Re: SD tune with variable geometry turbo
I have setup the sensor off a copper line on one setup but I have not logged it yet. Do you have any logs you might be willing to share? What size turbo and what is the setup and what sort of pressures were you seeing?
I did think of another potential issue but I would need to experiment further with actually implementing this to see how different solutions would work. That is the need for a wastegate on a gas engine and its control and interrelation with the variable turbine control mechanism. My first thought is to setup the turbine for the most aggressive spool in closed loop so it will stay closed until the desired boost level is achieved then set a manual controller for the wastegate slightly above the closed loop target so the turbine will stay full open once it has spooled up.
My question is what if you desire a variable boost target table? I would think the turbine control alone might work ok at lower throttle openings for a lower boost target but it will certainly creep at higher load and throttle and the wategate will still only be waiting as a backup at full boost. What about setting a generic closed loop output for the wastegate control solenoid using the boost target as the load axis? Set it just above the boost target pressure so it will only start to open after the turbine has lost control.
I did think of another potential issue but I would need to experiment further with actually implementing this to see how different solutions would work. That is the need for a wastegate on a gas engine and its control and interrelation with the variable turbine control mechanism. My first thought is to setup the turbine for the most aggressive spool in closed loop so it will stay closed until the desired boost level is achieved then set a manual controller for the wastegate slightly above the closed loop target so the turbine will stay full open once it has spooled up.
My question is what if you desire a variable boost target table? I would think the turbine control alone might work ok at lower throttle openings for a lower boost target but it will certainly creep at higher load and throttle and the wategate will still only be waiting as a backup at full boost. What about setting a generic closed loop output for the wastegate control solenoid using the boost target as the load axis? Set it just above the boost target pressure so it will only start to open after the turbine has lost control.