I have my WG dumping to atmosphere. While browsing the intraweb today I ran across some stuff that made me think about open WG dump pipes affecting AFR because not all of the exhaust is monitored. The info i was reading was suggesting that i could be running more lean than the sensor is showing. Or that is the most common side effect. Now i know others run open WG dump pipes for their external setups (mine is Tial). Anyone know any truth to this or have any experience with this?
This was all compared to running a downpipe with the WG reintroduced before the sensor so that it would read all the gas coming from the turbo.

 

The exhaust gas is more like a solution than a mixture. You'll have less volume going down the exhaust pipe, but it will be less volume of the same composition of gasses.

Here's one of them analogies.
You and your girlfriend go to marble slab and split a $6.95 strawberry shake. You have one cup of shake with 2 straws, you drink from one and she from the other. Are you both going to drink strawberry shake, or suddenly do you taste strawberry and she tastes vanilla?

Ben

 

I saw no effect. Nor would I expect to for the reasons noted above... unless you had reversion you won't either.

Mark

 

I have read that a leaky downpipe before the O2 will actually make the readings leaner than they actually are. But a mix is a mix, so I don't know why it would. Unless the decreased back pressure has some effect, if you were running a stock exhaust. Can't always believe what you read.

 

High exhaust back pressure will cause an O2 sensor to read richer. If release of the wastegate causes large changes in back pressure, it could change the O2 reading. I've only seen this mentioned when talking about placing an O2 pre-turbo in the manifold.

 

Couldn't have said it better myself.