Where is the best place to place them?

 

Do you mean a crankcase evacuation system driven by connecting a line from the crankcase, perpendicular to a high velocity section of the headers (eduction system)? If so, it going to pull air/vapor out of the crankcase, into the system, and if the O2 sensor is after the connection, its going to screw up the sensor readings.

 

So basicly if it is behind the o2 it should be Ok?

 

The exhaust gas has to be moving fast to create a vacuum in the evacuation line. The farther away you are from the engine, the slower the exhaust gas moves, because its cooling down. You should keep the connection at least a foot past the O2 sensor, so backwash at low RPM does not affect the sensor.

 

sounds good, Thanks