Pre Turbo 02 sensor

Hi everyone, I've a mad mid-engined prototype with a LSX Turbo . I'm building the exhaust system as we speak and it just occurred to me what difference does a post turbo 02 sensor make compared to a Pre Turbo 02... In my head the excess fuel and oxygen content still in the exhaust gasses tend to combust some what and would that not show up as a leaner mixture post turbo..... In my defense this would be my first EFI from scratch system so i may be over thinking it...... Thanks anyway for your comments Clive aka Dragon Prototypes

Despite what you might think, normally, combustion is complete before the exhaust valve opens.

What is a problem is that O2 sensors are sensitive to exhaust pressure, and mounting them pre-turbo means you really should be using one with pressure compensation (AEM had one, not sure if it's still available). So, mount your sensor post turbo....