[eschaider]

The closer to the exhaust port the better, Ace. The greater the distance from the exhaust port, the later the ECU will see the change in oxygen content and the later it will adjust the fuel mixture. While many ECU's have an adjustment for the timing of the changes based on the location of the sensor the inescapable fact is the farther from the exhaust port, the greater the time delay before the ECU can respond and the more potential detonation damage you expose the engine to.

If the sensor is just for tuning purposes with a carb then the time delayed response is less meaningful because the carburetor does not possess the ability to manipulate the fuel delivery in real time like an ECU does. That said, you still want the sensor as close to the exhaust port as is practical with or without an ECU to minimize any backwash of ambient air that enters the exhaust system from the open collector, skewing the sensor reading towards the lean side of it's range.


Ed