Just to echo what
@ZuMBLe has already said:
- The ecu meters fuel based on
calculated airmass
- It
calculates that airmass based on the flow characteristics of the engine (VE).
- The only sensors it has to do that are the air pressure (PUT, MAP, and ambient) and air temp. I.e. the airmass is based on the pressure and temperature of the air entering the engine, given that the engine can flow with xx efficiency at a particular operating point.
To put it plainly - you could run a hybrid on an is12 tune and your air/fuel will be fine. When tuning for a hybrid you need to make no changes to the airmass/AFR related tables.
Where you run into issues is that the closed loop boost control is only so reactive. Proactive (open loop) wastegate duty cycle is based on modeled values given certain known characteristics of the turbine housing. Hybrids blow that up entirely. So at a certain boost pressure, the ecu won't open the wastegate the right amount and it CAN lead to overboost situations. It's really only a problem at boost levels far above the is12 efficiency range (where the gate would need to stay closed for the little turbo to keep up.)
But I'm not a pro tuner, so what do I know.