GM.DYNAIR vs GM.DYNCYLAIR

[wadesns]

Based on what I have read and my knowledge from talking with others the gm.dynair is basically the hp that an engine creates and the gm.dyncylair is the torque. What I can not grasp is how they are computed. It only seems logical to me that the dyncylair should be dynair/(#of cyl) but if you look at a graph it obviously is not. So what exactly is the difference between the two other then the obvious one is total airflow and the other being airflow per cylinder? Also how can these numbers be converted into hp and tq numbers and would this be hp/tq at the flywheel? Is this how the ecm calculates engine load?

Here is an explanation of the two in a sticky I found:


GM.DYNAIR
PCM calculated airflow [g/s] based on VE.
Used in MAF rationality test and in MAF failed mode (speed density).


GM.DYNCYLAIR
PCM calculated cylinder airmass [g/cyl] based on VE.

[joecar]

Hi wadesns,

what graph are you looking at, can you post it;


yes, TQ tends to follow airmass[g], and HP tends to follow airflow[g/s]...

but also note that HP follows both TQ and RPM:

HP[hp] = TQ[ftlb] * RPM[rev/min] / 5252[ftlb*rev/min/hp]

(units are in [ ] square brackets)


the equations relating airmass (per cylinder) to airflow (per engine, i.e. N cylinders) are as follows:

( airmass[g] is DYNCYLAIR[g] and airflow[g/s] is DYNAIR[g/s] )

airmass[g] = VE[g*K/kPa] * MAP[kPa] / DAT[K]

airflow[g/s] = airmass[g] * RPM[rev/min] * N / 120[s*rev/min]
= airmass[g] * RPM[rev/min] * / 15[s*rev/min] when N = 8 cylinders

you can see that airflow[g/s] follows both airmass[g] and RPM, same as HP follows both TQ and RPM.


so for example, a typical VE would have VE = 2.2[g*K/kPa] at 100[kPa] and 6000[rpm]...

DYNCYLAIR[g] = 2.2[g*K/kPa] * 100[kPa] / 300[K] = 0.733[g]

DYNAIR[g/s] = 0.733[g] * 6000[rev/min] / 15[s*rev/min] = 293[g/s]

if you log DYNAIR, MAF, DYNCYLAIR, VETABLE_DMA you will see very close to those numbers.

[joecar]

To convert airlfow and airmass into flywheel HP and TQ you will need a few more parameters, for example cylinder pressure and/or compression ratio, ignition timing, fuel's energy density...

I don't have the equations handy, but the theoretical HP and TQ can be calculated from equations which consider the engine's physical dimensions/geometry.

[joecar]

Different ECM's compute load in several ways... for example: percentage airmass compared to maximum airmass; percentage MAP compared to BARO; throttle position; calculated torque (based on airmass and ideal ignition timing).

[joecar]

DAT[K] = dynamic air temperature [in Kelvin] = PCM's modelling/blending of intake air temperature modified by engine heat.

300K = 80°F which is a reasonable air temp for a Firebird with Ram Air (i.e. CAI).