So, looking this up for a friend. AEM has the wideband failsafe gauge for monitoring your air/fuel ratio. Do you need an EMS system to use that? Or can you use that gauge as a stand alone AFR monitor?

 

If you use the gauge stand-alone you'll have to drill another hole in the exhaust for the sensor since you'll be keeping the stock one so the car can still run but other than that and tapping a power source, you're golden. The question is raised as to why though, being that this means the car is still on stock ECU so there is already perfect management of this kind of thing in place for operating within the normal bounds.

 

Vortech v3 super with piggie-back management.