Ok, checked into Merc H/P engines...they are tuned on a dyno, without water, then ECM's burned so they do not use 02's on the production engines...

I'd run the exhaust completely dry. And I don't mean dry to the tailpipe end and mix water in. I mean pull the water out of the tails right before or right after the transom, and dump it away from the tail pipe via a hose/fitting/bung welded in.

Too loud you say? You can install some mufflers. Drill a small hole in the very end of the jacketed tailpipes right before the muffler. You just want a pisser of water to keep the mufflers from turning blue. The other 95% of the water will be dumping elsewhere via the bung/dump setup.

The problem with the 02's getting wet is a lot of times at idle speeds. You have some reversion going on, and full water mixing in, even far away from the sensor, can be enough to kill it. The 02's can handle a little bit of moisture, but they cant be getting sopping wet. Even cars get a little condensation in the pipes at times.

Something like this. See the water exit bungs?

That is how mine are setup now. There is a 1/4" hole about an 3" from the end of the pipe on the top side of the inner tube. In the video that is where the water coming out of the pipes is coming from but the majority is coming out the dumps. As you can see the 1/4" holes let quite a bit if water into the pixies, I wonder if reversion would still be a problem with the O2 sensor? I have never had a reversion problem but these things do sound sensitive. For me I would probably end up making an adaptor plate that goes between the manifold and the riser to install the sensor into!

http://m.youtube.com/watch?v=Xy-7UolI1No

Goog to know but I am surprised that they "set it and forget it"

I would think you want a setup that is always making small tweaks?? Opinions?

I thought you might fine this interesting. Aqua Power Ltd tested their mufflers on a boat that has reversion problems a couple of weeks ago. Open exhaust clearly had reversion at idle but when the mufflers were used there was no sign of it, the pipes were completely dry. One test doesn't prove that they always stop reversion but they did work on that engine.

Ezstriper, from your pics, it appears that you are running silent choice type exhaust. If so, then the water is entering the exhaust right at the end of the collector. That can't be more than 2-3" behind your sensor. If that's the case, you will never get a sensor to live. I have looked high and low for a sensor that can handle water and there is no such animal. They are all highly allergic to water.

It was asked previously what we do. We tune them on the dyno with O2's. We then tune them in the boat with O2's. Even if we have 2 engines that are completely identical, they will have slightly different cals. We almost never build the same engine twice since we are a custom builder and everyone wants what they want and everyone has different needs and budgets. Even if we did build the same engine again, I would never just put a cal in it and send it out the door. You might be able to get away with that on a 400-500 hp engine, but I wouldn't attempt it on something in the 1000 hp range. When tuning them in the boats, we do go through quite a few sensors unfortunately. I would say that I buy 15-20 per year. For a while, I had O'Reilly's swapping them out, since they have a 1 year warranty. They did it for a while but eventually they caught on that we aren't using them what they were intended for. We use Bosch sensors that are about $60 each.
Eddie

Eddie, excellent detailed answer - thanks from all of us who might benefit from your expertise. How long do the sensors typically last before they expire? I was thinking about installing a bung in one of my divorced collectors for my Lightning headers (they have an internal tube that slips into the collector to extend the dry run of exhaust). That would put the sensor about 4 inches from where the water is introduced. Is that far enough away if I don't use a muffler with it? I figured after the tune I could swap my set of silent choice collectors much like EZ has on his setup.

Thanks again!

The amount of time really depends, but it's not long. I would say that we get, on average, about 5 hours of runtime out of a sensor. I have 4 of the dual sensor FAST units and at least 12 sensors. It's hard to tell which ones I'm using since I just grab a sensor out of the box. Since I work on triple engine boats as well, I keep all 4 of the widebands and the sensors in one large waterproof case. It seems that everytime I tune a boat a have at least one sensor go out. Sometimes, 2 or 3 take a dump.

The distance they need to be in front of the water varies with engines. The larger the cam, the farther away the water needs to be. 4" isn't very much. If it is any sort of an aggressive cam then the sensor will probably get wet at idle. It should be fine while running though.
Eddie

Eddie - thanks for chiming in and I am a little glad that you deal with the same issues as some of these oter guys! If I convert to EFI my O2 sensors will be about 38" from where the water dumps in. I would assume I will be okay!