Does anybody know if there is a "good" place to weld in pyrometer bosses on CMI E-top headers? I plan to put O2 sensors in the tailpipes and see clearly where to do so, but am concerned about where the pyro bosses should go in. I am concerned about welding stress and cracks due to same. I figure location is critical. Any thoughts?

Different EGT kits will need to be at different locations in the primary tube. Too far from the exhaust port, and it will read low no matter what, too close and you'll get a high reading. Generally 2-1/2 to 3-1/2 inches from the exhaust port. Best bet is to determine what cylinders you want it in, and send them back to CMI and have them do it. What type of O2 sensor have you found that will live with water ?

Hi,

RumRunner is on target. In the perfect set up, you'd have 1 EGT sensor for each cylinder, mounted about 2 1/2 inches from the exhaust port. For pleasure boating however, that's pretty rare. Ours is mounted about 2 inches stern side of the collector on the center engine. It's an 18 mm bung that is welded on the inside and outside thru the water jacket. The outer engine sensors are mounted in the tail pipe about 1 inch stern side of the flange joint. We only use them for dyno work or lap top dial in of the ECM's, otherwise they are plugged.

We're getting pretty good general data with 1 per engine. What we can't tell with one, is if we have a particular cylinder leaning out from a bad injector. We will see an indication on the O2 sensor, but we wouldn't know which cylinder in particular was the culprit. Knowing we have a problem would hopefully allow a repair before a failure.

Best to have them installed by CMI if that's the brand of header you're running. Otherwise have the original header builder put them in to assure they are well sealed on both sides of the water jacket. As to stress and cracks, haven't experienced a failure due to the O2 sensor. Have indeed had problems with electrolysis or internal corrosion, but no cracking. Ask for Jeff at CMI, decent fellow and should take care of your needs.

Good luck,

Steve

Steve:

What kind of O2 sensors are you using now, and how are they living ?

Doug

Hi guys,
Spinetickler just had one welded onto his header in his Cigarette so we could read the 02 readings and CMI put his about 2" past the collector where all 4 pipes come together. Hopefully they put it in the correct place, we havent had a chance to do any readings yet to see how well that location reads. We'll keep you posted.

Pwrbt33
Offshore Performance

Doug,

We only use it on the dyno or when using the lap top on the water in real world running. So it probably doesn't see constant use in salt water for more than 1 hour. It's an aircraft O2 sensor, I don't recall the make, but I do remember it was something on the order of $900 when new. It's stainless. You might e mail Bruce, moderator of this section. He uses one in his shop in St. Louis.

Good luck Doug.

Steve

Steve:

Thanks, I've got NGK sensors we use, but @ $1100 each they get pricey when you want to use 8.

Doug

As far as the O2 sensor and water, I was figuring (hoping) that the sensor mounted in the elbow before the tailpipe flange would stay dry. The tailpipes don't dump water until a good ways astern of the flange. I know that you must keep an O2 sensor hot to get readings worth a flip, but planned to use sensors with integrated heating elements in them.

If somebody has had problems doing what I am planning, please sound out.

I will, however, send the headers to CMI for the proper installation of the ports.

RumRunner & mcollinstn,

Rum, I'm with you, that gets real expensive! For the type of boating I do, which is predominantly cruising with (WOT maybe 1 minute out of 60), 1 sensor per engine pretty much gives the info we need. I do make it a habit to check the plugs after a hard run to determine where we're at. Generally, they are a fair cocoa color, a tiny bit on the fat side.

mcollinstn, sorry I didn't make it clear about the O2 sensor and salt water. The "bung" is welded on both sides so the actual sensor doesn't get wet. However, in a salt water environment there will be some inevitable misting in the header, whether it be reversion or the ambient mist created by airflow thru the air ducts and digested by the blowers.

Sounds to me like you're on the right course.

Take care, good luck.

Steve