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Removing Cats from EXT CAT manifolds...

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Long story short... 2007 LSV23 with Monsoon 340. Engine has the EXT Cats manifolds. Boat has been running/stalling on the trailer since the thermostat started sticking. Cooling system is fixed. I changed the plugs/wires/cap&rotor. Pulled the rubber muffler coupling off the elbows/muffler and found a broken CatConverter in the muffler. I'm going to pull the manifolds and pressure test them for leaks then remove the other cat and test again.

REAL WORLD EXPERIENCE, has anyone run their Monsoon340 WITHOUT cats? What was the result?

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There is nothing extra special about the exhaust manifold gasket, but the Indmar gasket is a pretty good one.  Before catalyst exhaust, high temp silicone sealant was used to seal the manifolds to the head and there were no gaskets.

There shouldn't be any post cat O2 sensors or exhaust temperature sensors on the 2007 ETX CAT manifolds, so the only real problem you should have with no catalyst elements in the manifolds, or using non cat manifolds, is the increased CO and NOx coming out of the exhaust, but there shouldn't be any alarms or running issues.

There is a re-plumb kit available that keeps the ETX CAT manifolds cooler and extends the serviceable life of them.  I have been told that the re-plumb kit is required when replacing manifolds to get any kind of warranty coverage on the replacement manifolds from Indmar.

Edited by csleaver
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Previous owner of my boat didn't have the replumb kit when I bought my 08 VLX from him.  After one season, one cracked riser from surfing a lot on the starboard side (port side was higher in the air - gravity - means less water flow on the port side = leads to cracked riser).  Replumb kit made those new risers and that engine run MUCHO cooler.


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