I’m wanting to fit an Air/fuel ratio gauge to my car, however I have a stock downpipe, where’s the best place to weld a bung on the downpipe?

I run mine in the standard v3 onwards o2 sensor bung , as that position isn't used on the v1/v2.  

There was a spec sheet in my aem x wideband box that tells you where it's best to fit it . Unfortunately I threw it away but sure it said at least 18" from turbo outlet and slightly higher than horizontal. 

Mine has been fitted closer than 18" for about 4 years without issue but it makes sense to fit the sensor at a angle that wont let moisture pool in the sensor .So definitely fit it at a horizontal or higher angle 😉

Cheers for the help man