Thats a really nice looking Z3 there, also in Silver, must be fun with a revvy m44
I think turbo could be a issue for the RHD guys like NZ/SA/AUS/UK/JAP you know. At least it was for them in the 6 Cyl department, But I look forward to it. Let me know if you figure something out or help with prototyping things. Now as for engine management goes, since its M44, I think you would definitely want some larger injectors, delete the pcv system or use some brake boosters to ensure the crank case doesn't get pressurized, a good rising rate fuel pressure regulator, then maybe the innovative data logger with a wideband for afr, then find a good tuner. The maf will definitely need rescaling, I wonder if you can use a HPX PMAS? As the BMW MAF doesn't like being a blow through setup and even then they max out quite fast.
That said you may be able to save some money by just going to end tuning since you are in the UK, Enda does great work. Just get it tuned from there.
For wideband, innovative is good but which ever it is, put a off switch to the ground so the sensor will last a life time as in off when you dont use it.
If a simple manifold is what you are after and come up with a good concept, I could help R&D and develop it at our factory.
