Installing WB 02 in IMCO power flow elbow
 

Wanting to swap carbs and tune the AFR. I've heard you need dry pipes and I've also seen posts where folks have installed them in wet systems by drilling thru the 2 layers of the elbow and welding in bungs.
Will this work with low-rise elbows? How far fwd does the sensor need to be away from the point where exh and water mix? I've seen 15" quoted. Anyone got away with less?? I'm looking at less than 12"..

I know just a little bit of water hitting a heated sensor will destroy it.

Is it safer for the sensor when eng is at higher RPMs? Reason I ask is if it's less likely to get wet when on plane, I could hold off switching on the WB 02 heater until I was on plane. Then switching it off before coming off plane.

You should be ok with 12" from where the water enters the exhaust. You want to put the bung as close to the manifold as you can. When putting the bung in a jacketed pipe, there is an easy way to handle it. First, drill a hole through both pipes. In the case of the bungs I use, they are about 1" diameter, so we drill a 7/8" hole with a hole saw. Once you drill through both pipes, take a look at the gap between the 2 pipes. If it is small enough to Tig weld, then just weld up the gap. If it's to large to weld closes, then lay the rounded end of a ball pein hammer on the hole and hit it with another hammer. The rounded end of the ball pein will roll the edges of the hole in so that it tightens up the gap. Once the gap is small enough to weld, then weld it up. At this time, take the time to pressure check the weld. This will seal off the water so it doesn't leak. If it leaks, it will kill the sensor. You can just blow some compressed air through it while you put some soapy water on the weld. Once it sealed, them you can weld the bung on top of the pipe. You already sealed the water off, so the sensor can just be welded in place.
Hope this helps.
Eddie

Thx for the reply. Any thoughts on if a higher RPM will help keep the sensor dry? Seems like it would but I have very little experience with reversion.
To make matters more complicated, the engs have aftermarket cams and the prev owner doesn't know the specs or have any paperwork.

Reversion is only an issue at idle, or below around 1200 rpm or so. The exact rpm will vary based on cam, exhaust type, runner length, etc. The sensor will definitely stay dryer at higher rpm. However, you don't want to run the engine without the sensor powered up. That will kill it in no time. Your idea of turning off the sensor before slowing down will not work. You are better off keeping it powered up so that it has a chance to burn off any water that may hit it. Whether it gets wet or not, running the engine without the sensor powered up will take it's toll on the sensor in short order.
Eddie

That's what I thought, just wasn't 100% sure.

Thx Eddie!

What port's do you recommend putting the sensors in?

Put them in the collector of a header or the riser in a manifold setup. You want the O2 sensor to be at a point after all of the cylinders merge.
Eddie

Do you need to use a stainless steel bung and a special type of weld? I'm not a welder, so I have no idea. I was considering putting a set of bungs in the divorced collectors for my Lightning headers - they have a stainless steel inner pipe and a mild steel outer. Is there something special that has to be done with these, or just a regular old MIG or TIG weld?

I have heard of people putting them in the exh heat riser passage in the intake manifold. but I have a feeling it will only read exh from 1 or 2 cylinders.

Not to mention most aftermarket manifolds and heads do not have these passages.