To continue this discussion:
- The Limitation on the R34 not allowing TP higher than 255 may be the first legitimate reason I've seen for not performing a rescaling the way we are suggesting.
- The limitation of the S13 not being able to set a K constant high enough would also be a limitation.
It should be noted however that your proposed setup would result in TP SOMEWHAT being inaccurately referenced in other maps the ECU uses.
One thing that I think needs to be nailed down is the function of the MAF lookup table and it's relation to K and TP.
Do we agree that the MAF lookup table basically converts the non-linear voltage input to a data scale representing a percentage mass of air (g/sec)?
I look at it as a translation unit for the MAF we are using. Though the voltage is non-linear, the table lookup should be linear to airflow. meaning a 0 lookup value = 0g/sec and the maximum lookup value = max g/sec = 65535, along with every other value in between. The Nistune table even labels it as such with "percentage" as the second line in the table.
For example:
Z32 maf:
Lookup table
2v = 3111 = 4.7%
2.96v = 11189 = 17%
4v = 29324 = = 29234/65535 = 44.7% of full flow = 223.5hp
4.21v = 34864 = 53.2% = 266hp
5.12v = 65535 = 500hp
compared to a S14 Lookup table:
s14 maf:
2v = 4108 = 5.55%
2.96v = 12126 = 18.5%
4v = 30525 = 46.6% =
5.12v= 65535 = 100% = 266hp.
So now the ECU after looking up the Maf voltage, knows what PERCENTAGE of volume of air is coming into the engine (relative to the total capacity of the MAF).
This is where the K constant comes in. The ECU knows whether we are 10% or 100% of airflow, but it doesn't know how that corresponds to load on the engine and actual airflow. The K constant further converts that percentage flow to actual airflow.
Lets say we're on a stock s14 map.
K=33017
the Lookup table Multiplied by the K constant should equal the same thing regardless of what MAF we're running.
S14 maf: max HP = 33017*65535 = 2.16^10
If we switched to a Z32 MAF, the K would have to go up by 500/266 = 1.87x = 62062
Then lets say the engine is operating at the exact same HP level
266hp.
This will read about 4.21v on the Z32 maf. The lookup table will read 34864. multiplied by K = 2.16^10.
Though this is just for maximum HP. The same applies to all the other critical maps that rely on load (g/sec) or the TP (which is simply derived from RPM and load and injector size).
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Do we agree up to this point? If we can't agree that you should be able to change the MAF combined with K and run the engine exactly as is without changing anything, then we should settle that first.
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Some background (based on actual tuning, not theoretical), we found massive issues with using a HPX MAF (3" 640rwhp) calibrated on my R34 prior to FP, whilst we could get K constant set correctly during warm dyno runs, the K constant resulted in higher TP and therefore high vlaue TP scales, that all ended up affecting O2 feedback and warmup.
No one is arguing that the FP and TIM isn't needed. On the contrary, it is always needed for injector changes (or as I've now found out, in cases where K constant or TP value will "max out" due to binary reasons.
You also mention here that changing the MAF resulted in higher TP Scales. I think this is also an area you misunderstand us. When we chose to change maf, we are not advocating rescaling the TP index at the
same time. You can only adjust TP index if you tune or rescale the entire fuel and igntion maps.
Was this MAF swap combined with an injector swap as well? Or were you hitting much higher TP levels on stock injectors?
If you left the TP scales stock, swapped in the HPX maf, and decreased the K constant (probably a lot), it should track the exact same cells as it did before the MAF swap (on stock injectors). If VTC kicks in at TP=24, then it should do that at that TP regardless of the MAF. If you are now wanting to increase Boost, you will be accessing TP values that are not even in the Fuel or ignition map. This is when you'd have the adjust index values to make room, and at the same time appropriately "compress" the stock map into fewer columns. This would require properly setting O2 flags for cells and such. But creating more room in the fuel maps for higher boost has no effect on the ECU knowing that TP =24 is the time to kick on VTC.
Current scales:
24 32 40 48 56 64 72 80 88 96 104 112 120 128 144 [160]
New scales
41 55 68 82 96 110 124 137 [151] 165 179 193 206 220 248 255
At 12psi where our MAF reads previously at 160 at full boost, looking at the above table we should now be maybe half way here. However VQ map is exponential, so actual position may be less with the Z32 MAF
1) The above scale would be bad
a) because you now have no lookup values near 24 in your new scale. These would be the low load values. While the new scale maximum can change, the base should stay the same. driveability would be bad.
b) The fact that the map traces near the middle should not effect driveability. if 160 was in fact your maximum load you'd expect, It would be a very poor use of the map, as you have lower resolution and would never use any of the area on the right of the map. We still would agree that the maximum TP load you need should correspond to the horsepower range you're expecting to run the engine in. But we believe it should be set by adjusting the index, as opposed to the K constant. And if you do adjust the Index, you better move the map data to proper corresponding columns.
One area I may have overlooked is if the INDEX values are used in other maps. Since they are specifically specified for Fuel and Igntion tables, I assume they are not used elsewhere. I believe elsewhere, the ECU uses the current reading TP value, not the index position or column number.
Thank you for highlighting the facts of sometimes hitting binary limit on K constant or Load value.