EagleMark
03-25-2011, 02:03 AM
This conversation was started elsewhere and copied here
EagleMark Said: The $42 has been around a long time, wondering if there is any more in there to get like Injector Size, cylinder volume etc... I see these in maf chips and the 16197427.
Robert Saar Said:Glenn, it sounds like you're referring to the $42 XDF.
it's a bit OT, but i can elaborate on it a bit since it's came up before.
the $42 mask(and quite a few others as well) doesn't use an injector size scalar or a cylinder size scalar either... they are actually both combined into a single scalar/table, usually referred to as BPC/BPW vs EGR%.
couldn't tell you why GM did this, but you'll notice that as EGR% increases, the value decreases, this is due to the gases recirculated by the EGR valve(s) taking up space that combustible air would otherwise occupy, so less fuel is needed, this is how the ECM accounts for that.
so, knowing that smaller numbers deliver less fuel, you can now account for injector flow and engine displacement changes.
larger injectors need a smaller number.
more displacement needs a larger number.
ideally, get an engine tuned on stock injectors(idle fueling correct at least), then:
change your injectors and adjust the BPC/BPW table/scalar until the fueling is corrected again(without playing with the VE tables since VE should not have changed from injectors alone)
or
bore/stroke/drop in a different block with the original injectors and adjust the BPC/BPW until correct. if you go far enough you'll likely need larger injectors on a larger engine anyway, so you can probably skip this step if necessary and make intelligent decisions about VE and BPC/BPW values.
EagleMark Said: wow thanks for the time to share that! Big light went off in my head why that engine I tuned with EGR DELETE was so far off...
Now my question is: If EGR is turned off and everything in chip for EGR is deleted? Where would you make these big changes before you start messing with VE tables?
EagleMark Said: The $42 has been around a long time, wondering if there is any more in there to get like Injector Size, cylinder volume etc... I see these in maf chips and the 16197427.
Robert Saar Said:Glenn, it sounds like you're referring to the $42 XDF.
it's a bit OT, but i can elaborate on it a bit since it's came up before.
the $42 mask(and quite a few others as well) doesn't use an injector size scalar or a cylinder size scalar either... they are actually both combined into a single scalar/table, usually referred to as BPC/BPW vs EGR%.
couldn't tell you why GM did this, but you'll notice that as EGR% increases, the value decreases, this is due to the gases recirculated by the EGR valve(s) taking up space that combustible air would otherwise occupy, so less fuel is needed, this is how the ECM accounts for that.
so, knowing that smaller numbers deliver less fuel, you can now account for injector flow and engine displacement changes.
larger injectors need a smaller number.
more displacement needs a larger number.
ideally, get an engine tuned on stock injectors(idle fueling correct at least), then:
change your injectors and adjust the BPC/BPW table/scalar until the fueling is corrected again(without playing with the VE tables since VE should not have changed from injectors alone)
or
bore/stroke/drop in a different block with the original injectors and adjust the BPC/BPW until correct. if you go far enough you'll likely need larger injectors on a larger engine anyway, so you can probably skip this step if necessary and make intelligent decisions about VE and BPC/BPW values.
EagleMark Said: wow thanks for the time to share that! Big light went off in my head why that engine I tuned with EGR DELETE was so far off...
Now my question is: If EGR is turned off and everything in chip for EGR is deleted? Where would you make these big changes before you start messing with VE tables?