I just ran across this website that says a Bosh LSU 4 wdeband is as much as 15% inaccurate at 2 bar (29 psi) exhaust pressure. Has anyone heard this? How high does exhaust pressure get in our truck's exhausts, between the engine and the turbo?
I just thought that I would present this for discussion.

 

Us turbo guys don't run the WB pre turbo. I always install a bung in the down pipe for wb after the turbo. I did a pressure check on a customers truck a while back and only saw 1-2psi in the down pipe.

 

OK, so in a right-side turbo, it is only the narrowbands that I have read about, the left one between the left and right manifolds, and the right one between the right manifold and turbo? I never paid attention to the location of the wideband.
And it wouldn't matter for the narrowbands since the engine is in open loop at that point.

 

I see on their graph that at 1.2 bar, the error is 5%. So I imagine that (17 psi) is a high pressure on the engine side of the turbo? Anyway it doesn't matter if nobody mounts their wideband on the engine side of the turbo.

 

Yep, you are correct in your thinking of where the narrows go and that they in open loop at WOT.

And 1.2 bar the way they are talking about it is only 3psi. 1 bar is NA. Less than 1 bar is vacuum.

I good turbo setup is about 1:1 with boost/back pressure but 1:2, even 1:3 in high boost applications isn't unheard of.

 

Most of the typical turbo kits for these trucks have about 2:1-3:1 backpressure/boost depending on turbo size, engine size, rpm, and boost. Really really good is 1:1-1.5:1, but by good I mean flows well at high rpm. One with that low of backpressure will be much lazier and is really meant for race only.

 

If nothing else, this thread can serve as a warning to not install the wideband pre-turbo, and gives the reason why.