I have HPT's 2 bar speed density program for my truck. We were wondering ..How the timing table knows what kpa the vehicle is at since it still uses Mass Air numbers ?

Thanks

 

so you don't plan to use the MAF? speed density program doesn't mean it has to be in SD. U plan to be FI...that's a turbo in the pic, wouldn't it be advantageous to use the MAF?

I am sure the answer to your qeustion has to do with running equations from the VE table.

 

When in SD (and not in SD), the PCM converts the values in the VE table to airmass units that directly relate to those in the timing tables.
Equation listed in EFI Live is:

The air mass per cylinder can be determined from the VE table using the following formula:
g/cyl = VE*MAP/charge temperature
Ve is in g*K/kPa,
MAP is in kPa,
charge temperature is in degrees Kelvin.

When not in SD, the PCM uses a "blend" of the MAF and VE table values.

 

gms/cyl is not related to MAP.

Well, it is, but it isnt. gms/cyl is not derived from the reading from the MAP sensor typically speaking. Although, if the MAF is gone altogether, then there's another way to get those values.

 

It is calculated from the value referenced at a specific MAP/RPM value in the VE table AND through the MAF sensor calibration. The default PCM units for VE is Grams*Kelvin/kPa. Without the MAF, the ONLY way for the PCM to retrieve g/cyl is through the VE table.

 

Interesting info ... this just elaberates even more why the VE table should be spot on.

 

No not using maf, yep FI . Don't know if it would be advatageous to use the maf, but it does ok like this.

 

Thanks for the info

 

So.........Why didnt they change the reading to KPA under the timing table? Like most standalone unit just makes it easier to read . Does anyone have a table converting GMS to KPA

 

Dunno what the thought behind it is, but having it in g/cyl allows more precision than the other kPa tables in the PCM.

Also, in a boosted motor with stock MAP, you run blind on any MAP-based table while in boost. That is not that case with timing in g/cyl.