low dyn cyl air ?
low dyn cyl air ? what would cause relatively low Dyn Cyl Air on a heads/cam/bolt on car ? stock MAF, long tubes, full exhaust...only seein .73 at WOT in 4th gear....timing is at 26, AFR 12.9...thanx
IDK about HPT .pids. You might want to make sure you have the right one selected - especially if you have as many as we do. I know in EFI Live, we have a .pid that's a direct look-up* for cylinder air mass for when we are in MAF mode and a different direct look-up* .pid for when we are in SD. These are the ones to use for spark reference.
There's also the GM.DYNCYLAIR.pid that's considered a 'predicted' air mass value. I don't use that one because I want actuals, not predicted. Then, we have a general, calculated .pid that takes the MAF airflow (in grams/second) and multiplies it by 15/RPM. I don't use that .pid either becuase I'm not sure if the MAF is 100% correct.
*FYI for the EFI Live guys - Direct look-up .pids are distinguished by their Parameter name on the PIDs (F8) tab. They all end in _DMA, which stands for Direct Memory Access. The data from these .pids is pulled directly from the operating RAM as the current conditions the PCM is operating under. Further details about DMA .pids are available in the help file for the scanner (hit F1 and scroll to page -88- of the document).
There's also the GM.DYNCYLAIR.pid that's considered a 'predicted' air mass value. I don't use that one because I want actuals, not predicted. Then, we have a general, calculated .pid that takes the MAF airflow (in grams/second) and multiplies it by 15/RPM. I don't use that .pid either becuase I'm not sure if the MAF is 100% correct.
*FYI for the EFI Live guys - Direct look-up .pids are distinguished by their Parameter name on the PIDs (F8) tab. They all end in _DMA, which stands for Direct Memory Access. The data from these .pids is pulled directly from the operating RAM as the current conditions the PCM is operating under. Further details about DMA .pids are available in the help file for the scanner (hit F1 and scroll to page -88- of the document).
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I am seeing similarly low CylAir on the H/C/I car I've been working
on. I suspected the MAF, swapped on my saved virgin stocker and
it changed from 0.71 to 0.76, still well short of the 0.80 - 0.84 I
saw on mine (with less mods, but a good commanded=actual tune).
With the low airflow numbers the car apparently was showing lean
on the dyno.
Dynamic Cylinder Air and Dynamic Airflow follow MAF airflow pretty
much, at least up top. It will vary some with elevation (your BARO
vs 105kPa). Me, I'm 4 feet above sea level.
I wonder what the ideal CylAir number is for our displacement and
100kPa ambient. Too lazy to try and calculate it. But that would
be a good sanity check for a 4000RPM WOT number (where the
airflow is not limiting it).
on. I suspected the MAF, swapped on my saved virgin stocker and
it changed from 0.71 to 0.76, still well short of the 0.80 - 0.84 I
saw on mine (with less mods, but a good commanded=actual tune).
With the low airflow numbers the car apparently was showing lean
on the dyno.
Dynamic Cylinder Air and Dynamic Airflow follow MAF airflow pretty
much, at least up top. It will vary some with elevation (your BARO
vs 105kPa). Me, I'm 4 feet above sea level.
I wonder what the ideal CylAir number is for our displacement and
100kPa ambient. Too lazy to try and calculate it. But that would
be a good sanity check for a 4000RPM WOT number (where the
airflow is not limiting it).
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So a 85-90 GM.DYNCYLAIR.DMA would be consider good at WOT on a H/C/E car? (98 Ls1 logged with EFILive with grams/cylinder).
Does nitrous have an affect of this calculation?
I just see that my 98 PCM used that PID and RPM to calculate HIGH OCTANE SPARK (B5913)
Does nitrous have an affect of this calculation?
I just see that my 98 PCM used that PID and RPM to calculate HIGH OCTANE SPARK (B5913)
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Joined: Apr 2002
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From: So.Cal.
Stock runs out at 0.76-0.77 g/cyl.
H/C takes it up from there, typically 0.80-0.90 g/cyl depending on H and C.
My understanding:
GM.DYNCYLAIR [g/cyl] and GM.DYNCYLAIR_DMA [g/cyl] are computed from VE.
GM.CYLAIR_DMA [g/cyl] is computed from MAF.
H/C takes it up from there, typically 0.80-0.90 g/cyl depending on H and C.
My understanding:
GM.DYNCYLAIR [g/cyl] and GM.DYNCYLAIR_DMA [g/cyl] are computed from VE.
GM.CYLAIR_DMA [g/cyl] is computed from MAF.
Seems to be around .91 g/cyl at WOT.
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