Thru transom dry exhaust.
03-12-2026 | 04:00 AM
#11
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From: Finland
Dry exhaust frome what I know is only used for Cam overlap issues. The other thing it is loud. In my new build it has to be Dry for the Cam overlap. There is about a 10 inch drop from the header collectors at a 45 degree angle to the exit out the transon. The O2 sensors are in the header collectors, they are very sensitive to mosture as well. Outside pipe is 4.5 inch OD and inner is 4 inch ID. I am welding up the lower half to the tails at the exit end to retain some water at idle but think the pipes will be full with the pump I am using. A small hole in the bottom is added for drainage after the engine is off. The top half the pipes are open with the standard 1/8-3/16 inch gap betten the innner and outer pipe. This will caise the water to go out over the exhaust and quite it down some as well. I can not see how any water at idle could travel up a 45 degree incline with a 10 inch rise but we will see. I'll have to carry a few O2s just in case it could. An O2 failure would show any water intrusion well before getting to the valves at idle.
03-12-2026 | 10:34 AM
#12
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Your tail pipe Angles/style looks exactly what I am doing right now, except mine IS going to Be with 3.5" innner Pipe and 4" outer. Do you Have a picture of 02 sensor bungs location?[/QUOTE]
I don't have a photo od O2 bungs. But the headers are CMIs and the bungs are in the collectors and straight out the side, in the standard location for boats. One in each collector.
I don't have a photo od O2 bungs. But the headers are CMIs and the bungs are in the collectors and straight out the side, in the standard location for boats. One in each collector.
03-12-2026 | 03:17 PM
#13
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From: Omaha/LOTO
This is what I have for a dry exhaust. First time for me as well and think it will work. Any input would be helpful.
Baffles are for two reasons, for reducing sound at idle and stop reversion. They bolt in at tail end. Old school spiral baffles that do work at idle but no real reduction at anything past half throttle.
Baffles are for two reasons, for reducing sound at idle and stop reversion. They bolt in at tail end. Old school spiral baffles that do work at idle but no real reduction at anything past half throttle.
Even if your tails were normal wet and mixed just inside the transom, I can't see them sucking any water back up with that much downward angle.
03-16-2026 | 04:26 PM
#14
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From: Finland
You Mean here.
03-16-2026 | 09:52 PM
#15
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Yes, that is the spot, same in each collector.
Not easy to put a O2 bung there after the fact. The O2 bung will be fine in the front of the tail pipe just after the clamp maybe an inch or two, should be easy to weld in there.
Not easy to put a O2 bung there after the fact. The O2 bung will be fine in the front of the tail pipe just after the clamp maybe an inch or two, should be easy to weld in there.
Last edited by LakeBoat4; 03-16-2026 at 09:57 PM.
03-16-2026 | 10:11 PM
#16
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Found a photo of the O2 bung hole in my collectors. Look at the crossover bung on top of the collector. The blue tape under it is the O2 bung hole.
Acually on another boat the O2 bungs are in the tail pipes as they were added with the new EFI system last year.
Acually on another boat the O2 bungs are in the tail pipes as they were added with the new EFI system last year.
03-17-2026 | 11:14 AM
#17
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This is what I have for a dry exhaust. First time for me as well and think it will work. Any input would be helpful.
Baffles are for two reasons, for reducing sound at idle and stop reversion. They bolt in at tail end. Old school spiral baffles that do work at idle but no real reduction at anything past half throttle.
Baffles are for two reasons, for reducing sound at idle and stop reversion. They bolt in at tail end. Old school spiral baffles that do work at idle but no real reduction at anything past half throttle.
Then installed 3/4 stainless bungs on the top side of tails per CMI recommendations 6" back from the inner transom wall. Plumbed accordingly out the side of boat. 4 yrs later no cracks from welding
the tails up. Basically no signs of water reversion. I'll see if i can post picts later tonight.
