I was explaining some stuff to some people on a volvo forum and I think it might be helpful to anyone doing a little modding. This mainly applies to people with turboed cars. This is not a 100+ whp mod (you will need a giant APC windshield sticker for that) but just a little tip that can make things easier down the road.

What I am suggesting is a Mod that I feel should be made by anyone upgrading their DP or exhaust where the initial O2 censor is placed. I am proposing that you should make a place for an additional O2 censor. The Reason for this is 2 fold. 1: you will want to get a Yband a/f gauge eventually if you keep modding and this is where this O2 censor will need to go anyways. 2: If you are modding then you are the type of person that will end up on a dyno at some point. This hole can be used for air/fule readings on the dyno and be made more easily accessible and you can leave your factory one where it is so to not throw a CEL.

The cost. I would be suprised if this mod even cost 30 bucks. It is mostly labor and takes 5 minutes and a welder.

How to. You will want to drill a hole in the DP and weld the appropriate nut to the DP with the same threads an O2 censor will use. If the hole is not going to be used then get a screw(with corresponding threads) and a washer and screw it in the hole till you need it down the road. One thing that is important here is placement. You need to ensure that when the flow goes through the exhaust that it can pass evenly by the censors. In other words stagger them a little and don't put one right behind the other. Here are a couple shots of mine.