PI : DI Ratio Discussion

[Kodename47]

A01G is the same as A02G.

B01C (and all C series OFT Defs):

<table name="PI Ratio Thresholds" storageaddress="10DE04" />
<table name="PI Ratio Threshold (RPM)" storageaddress="10DE14" />
<table name="PI Ratio Threshold (Load)" storageaddress="10DE18" />

B01D (and all D series OFT Defs):

<table name="PI Ratio Thresholds" storageaddress="10DDC4" />
<table name="PI Ratio Threshold (RPM)" storageaddress="10DDD4" />
<table name="PI Ratio Threshold (Load)" storageaddress="10DDD8" />

A01I (and all I series OFT Defs):

<table name="PI Ratio Thresholds" storageaddress="10C6CC" />
<table name="PI Ratio Threshold (RPM)" storageaddress="10C6DC" />
<table name="PI Ratio Threshold (Load)" storageaddress="10C6E0" />

NOTE: I have copied these direct from my definition, the names have been edited slightly so you will need to correct them or make them the same as ztan's above for them to appear. I shall update my own definitions for download later today.

[KoolBRZ]

Originally Posted by ztan

Def for above A01G:

    <table name="PI_Ratio_Thresholds" storageaddress="10C70C" />
    <table name="PI_Ratio_RPM_Threshold" storageaddress="10C71C" />
    <table name="PI_Ratio_Load_Threshold" storageaddress="10C720" />
    
    <table type="2D" name="PI_Ratio_Thresholds" category="Fueling - Injector Ratio" storagetype="float" endian="little" sizey="2" userlevel="4">
      <scaling units="PI Ratio %" expression="x*100" to_byte="x/100" format="0.0" fineincrement="5" coarseincrement="10" />
      <table type="Static Y Axis" name="" sizey="2">
              <data>PI Ratio 0% under</data>
              <data>PI Ratio 100% above</data>
       </table>
      <description>If PI Ratio RPM and Load Thresholds are not exceeded, PI Ratio is set to 0% if this value is not exceeded</description>
    </table>
    <table type="2D" name="PI_Ratio_RPM_Threshold" category="Fueling - Injector Ratio" storagetype="float" endian="little" sizey="1" userlevel="4">
      <scaling units="Engine Speed RPM" expression="x" to_byte="x" format="#" fineincrement="250" coarseincrement="1000" />
      <table type="Static Y Axis" name="" sizey="1">
              <data>PI Ratio thresholds not applied above</data>
       </table>
      <description>If this RPM threshold is exceeded, PI Ratio full on and full off thresholds are not applied</description>
    </table>
    <table type="2D" name="PI_Ratio_Load_Threshold" category="Fueling - Injector Ratio" storagetype="float" endian="little" sizey="1" userlevel="4">
      <scaling units="Load g/rev" expression="x" to_byte="x" format="0.0" fineincrement=".05" coarseincrement=".2" />
      <table type="Static Y Axis" name="" sizey="1">
              <data>PI Ratio thresholds not applied above</data>
       </table>
      <description>If this Load threshold is exceeded, PI Ratio full on and full off thresholds are not applied</description>
    </table>

Does that show the limits that are already there, or does it impose new limits?

[Kodename47]

Originally Posted by KoolBRZ

Does that show the limits that are already there, or does it impose new limits?

Say what??

[KoolBRZ]

I went for a drive with PI showing on my OFT. PI was off almost all the time. That means that those are the limits that were already there. Then I came back and added this code to my def file. I changed the lower limit to 19%, and filled my PI tables with 20 and 24 percent cells. Went for a drive again and this time watched PI and DI on my OFT. Now they are both working all the time, except when I idle, or decelerate. This is a really good addition to RR. Thanks @ztan
P.S. My hyper-sensitive butt-dyno feels like there is more low-end torque now with the PI running all the time. @shr133 You've got to get this code added to your def, so you can use these controls to run PI all the time. Your theory seems right. It definitely feels like it runs better with PI on all the time.

[KoolBRZ]

Here's a pic of what I'm trying now. I lowered the PI percentage and threshold even more. I think even 20% might be a bit much. Here's a pic of what I changed so you can see for yourselves what I'm talking about. I lowered it to .047 in the middle of my cruising rpm's to see if I can get a bit better mileage.

[thambu19]

Originally Posted by KoolBRZ

Here's a pic of what I'm trying now. I lowered the PI percentage and threshold even more. I think even 20% might be a bit much. Here's a pic of what I changed so you can see for yourselves what I'm talking about. I lowered it to .047 in the middle of my cruising rpm's to see if I can get a bit better mileage.

Interesting. Do you think the drive feel could better with higher percentages of PFI?
In part load conditions PFI wins hands down especially as the speeds increase. At lower speeds OEMs use DI to have better fuel control. PFI tends to have a puddle effect and OEMs sometimes even have a puddle model (accumulation and evaporation model)
The change you are feeling could be down to the fact that as we switch from DI to PFI without changing spark we are changing the location of peak cylinder pressure (LPP) to a more advanced position. This is because the charge cooling effect of DI makes the combustion speed slower and hence to get same LPP we need a bit more spark advance. Now when we keep the same spark advance and just change the ratio we can be speeding up combustion. So how does this help in the drive feel.
Okay so in combustion there is something called Combustion variance. This is the variability in LPP cycle to cycle. Typically there is a LPP that gives best torque/efficiency at a certain speed. Say for example at 1200rpm it is 14deg ATDC (just an example). OEMs generally tune spark to get the LPP at this precise angle. But it has been observed that as you advance the LPP a bit closer towards TDC say by a degree or so the variance in LPP drops but efficiency suffers. Meaning combustion gets more consistent but less efficient. Now for drive feel this variation in LPP is critical but for fuel economy it is not.
If I were to tune a race car I would tune it differently than tuning a street car for FE.
Back to the topic. By adding more PFI at same spark timing we are advancing LPP slightly and as a result getting better feel.

As a science experiment we should feel a better idle, accel, etc when we add a degree or so spark across the part throttle region (non knock limited). This should feel much like the way it felt with more PFI.

Okay so a lot of I said is theory, yes but being a dyno/vehicle calibrator myself I have experienced most of this.

[KoolBRZ]

Originally Posted by thambu19

Interesting. Do you think the drive feel could better with higher percentages of PFI?
In part load conditions PFI wins hands down especially as the speeds increase. At lower speeds OEMs use DI to have better fuel control. PFI tends to have a puddle effect and OEMs sometimes even have a puddle model (accumulation and evaporation model)
The change you are feeling could be down to the fact that as we switch from DI to PFI without changing spark we are changing the location of peak cylinder pressure (LPP) to a more advanced position. This is because the charge cooling effect of DI makes the combustion speed slower and hence to get same LPP we need a bit more spark advance. Now when we keep the same spark advance and just change the ratio we can be speeding up combustion. So how does this help in the drive feel.
Okay so in combustion there is something called Combustion variance. This is the variability in LPP cycle to cycle. Typically there is a LPP that gives best torque/efficiency at a certain speed. Say for example at 1200rpm it is 14deg ATDC (just an example). OEMs generally tune spark to get the LPP at this precise angle. But it has been observed that as you advance the LPP a bit closer towards TDC say by a degree or so the variance in LPP drops but efficiency suffers. Meaning combustion gets more consistent but less efficient. Now for drive feel this variation in LPP is critical but for fuel economy it is not.
If I were to tune a race car I would tune it differently than tuning a street car for FE.
Back to the topic. By adding more PFI at same spark timing we are advancing LPP slightly and as a result getting better feel.

As a science experiment we should feel a better idle, accel, etc when we add a degree or so spark across the part throttle region (non knock limited). This should feel much like the way it felt with more PFI.

Okay so a lot of I said is theory, yes but being a dyno/vehicle calibrator myself I have experienced most of this.

I just made several tunes with slightly different tables. See pic below. I'll let you know which one seems best.

[Kodename47]

@KoolBRZ if you want full ratio control above idle, don't worry about the max/min ratio just set the load and RPM thresholds to around 1000/0.2. In your setup, the 5% DI will run no PI at all,so in your cruising you'll be full DI and I'd avoid that for the cleaning effects of PI.

[thambu19]

Originally Posted by KoolBRZ

I just made several tunes with slightly different tables. See pic below. I'll let you know which one seems best.

Id be surprised if there was any difference at all because the amount being changed so small between the different cals.

[KoolBRZ]

I think you both have good points. I changed the injection ration thresholds to be off above .2 Load, and above 500 RPM, and also raised the lower limit to 74. I then added more percentage to each of the three tunes, so the changes would be more definitive.

[KoolBRZ]

Full time PI isn't looking good so far. I'm getting only 26 highway mpg on tunes 20 and 21. Loaded tune 22 just now. We'll see how it goes.

[KoolBRZ]

Strangely enough, more PI, in tune 22, sucked less than tunes 20 or 21. I have a Phantom ESC, and found 22 works better under light boost, (~3 PSI), than 20 or 21. It's obvious the PI thresholds are to enable mileage as high as 30 mpg.
So, if PI automatically cuts off when the throttle is zero, and I only want PI at off-idle tip-in, and above 5200 under higher loads, the thresholds still do me no good. I've rescaled it and changed the tables, but I'm still not turning them on, off, and on again. Now they are on, then off, or just on. depending on the load.

[KoolBRZ]

I tried the table shown, 23, and a new one, 24, which turned out to be better. From the stock thresholds and my experiences, I conclude that anything less then 35% is worse than nothing, and anything more than 75% might as well be everything. I'll keep on trying out different tables and posting them here, all by myself. (sound of crickets chirping)

[KoolBRZ]

This is almost the same as the ESC OTS tune's table and threshold. I lowered the RPM's to 2200, raised a few cells, rescaled the rpm range, but it's very close to the way it started.