MGP vs MAP for Turbo GDI

[Scott33]

I'm curious why it's recommended to use MGP instead of MAP as an axis for the fuel table.  If we consider two scenarios, both with the same MAP/IAT value, both with the same Fuel pressure level, but at different BAP values, then IMO:

1. The mass of air in the manifold is the same (same MAP/IAT = same mass, unless the manifold changed size?)

2. The mass of air in the cylinder is the same, for the reasons above

3. The fuel injected for a given pulsewidth is the same (same fuel pressure as stated above, and same pressure where the fuel is being injected into due to 1/2 above depending on whether direct injection or not)

The only things I see being different are exhaust backpressure (but that just affects how much effort it is to push the mixture out) and different crankcase pressure (but I don't see why that matters).

I do think it's important to take BAP into account when creating target boost levels (since the turbo may not be able to generate high boost levels at altitude simply due to the lower density of air, which may result in the turbo heating up), but that's not actually configurable AFAICT.

Anyways, if you could clarify how MGP results in better fueling tables for turbo engines, direct injection or not, I'd appreciate it.  Thanks!

[Scott33]

bump.. I think I posted this when everyone was still on vacation. 

[Adamw]

There is some theory's for and against, but here is an explanation: 

 

Most theory suggests MAP divided by BAP would be a more correct way to model it but I believe Link originally came up with the strategy and proved it when many of their customers where involved in a popular hill climb here called "Race to the sky".  I have recently tested it pretty well with a gyrocopter (NA) and was surprised how well lambda stayed on target over its full working range.