Unless I'm not understanding everything correctly, a turbo IP should behave exactly like a NA IP until the ALDA sees boost in the intake manifold. Right? Because a turbo motor at idle behaves just like an NA motor, no boost and just taking in an air charge at 14.7 psia.
The only thing I can think of is that the 2 valve 60x engines use 115 bar injectors for NA and 135 bar injectors for turbo engines. If the 4 valve motors are the same, perhaps your timing is off because of that? I don't know, I'm just thinking aloud.
I'm curious as to what you'll find out OP.
