If the BOV isnt 100% atmospheric then that allows some air back into the engin, thus keeping teh car from running to rich between shifts.
If its 100% atmospheric and non adjustable then usually they come with a fitting to seal off the recirc hose.
However I wouldnt run 100% atmospheric, at least not with a basic tune
- Mike
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Rally driving, when you're fertile enough to impregnate women with eye-contact