achris
More fish than mountain goat
- Joined
- May 19, 2004
- Messages
- 27,468
Exhaust systems 101
Mercury’s introduction of ‘dry-joint’ manifolds (and elbows) seems to have caused more confusion than it needs to. So let’s try to unpack that confusion, and understand what is essentially a very simple system.
Before we go much further here’s a picture of the various parts of the exhaust system and their names, so we are all talking the same language.
Wet-joint vs dry-joint.
This seems to be where the most confusion arises. What is wet-joint and dry-joint?
Merc introduced dry-joint exhausts in 2002 in response to a common problem, the metal between the water jacket and the exhaust cavity was ‘under attack’ from both the sea water (salt) and the red hot exhaust gases. Most manifold replacements were because of this problem, and when the joint failed, water would enter the engine cylinders, usually with expensive consequences.
Here is the ‘wet-joint’ exhaust system.
This is the ‘dry-joint’ system.
As you can see, the dry joint has those thin walled water passages closed off so there is no longer a corrosion failure point, and the water flows through specially cast passages to the sides of the joint.
I have also seen confusion arise from the raw water/closed (fresh) water systems.
In a raw water cooling system, all of the engine (heads, block, manifolds) is cooled by sea water (or lake if you’re not in the sea) and flow through the engine, heads and into the manifolds then up to the elbows through ‘open’ gaskets.
In closed (fresh water) cooling the engine (heads, block, manifolds) is cooled by coolant that is cooled by sea water in a heat exchanger. The gaskets between the manifold and elbow (or riser if risers are being used) are closed, keeping the coolant in the manifold and separate for the sea water in the elbow.
The only exception is a ½ closed cooling system, where the heads and block have coolant and the exhaust manifolds have sea water, in which case you would want open gaskets.
The elbows themselves are also quite different and easy to identify by just a quick look.
Changing from raw to closed cooling does not change the system from wet to dry. To change from wet to dry, you need to replace the manifolds and elbows (and risers if you’re using them)… And you can't 'mix and match'. If you have dry joint manifolds, you MUST use dry joint elbows and risers. Conversely, wet joint manifolds can only have wet joint elbows and risers on them.
I hope this clears up the confusion.
As always, comments below if you have any. (And for the really experienced guys, this is a brief overview, an introduction, not a detailed explanation of every aspect of exhaust design. Yes I’m looking at you @Scott Danforth .
) If well received, I'll add it to the stickies.
Chris....
Mercury’s introduction of ‘dry-joint’ manifolds (and elbows) seems to have caused more confusion than it needs to. So let’s try to unpack that confusion, and understand what is essentially a very simple system.
Before we go much further here’s a picture of the various parts of the exhaust system and their names, so we are all talking the same language.
Wet-joint vs dry-joint.
This seems to be where the most confusion arises. What is wet-joint and dry-joint?
Merc introduced dry-joint exhausts in 2002 in response to a common problem, the metal between the water jacket and the exhaust cavity was ‘under attack’ from both the sea water (salt) and the red hot exhaust gases. Most manifold replacements were because of this problem, and when the joint failed, water would enter the engine cylinders, usually with expensive consequences.
Here is the ‘wet-joint’ exhaust system.
This is the ‘dry-joint’ system.
As you can see, the dry joint has those thin walled water passages closed off so there is no longer a corrosion failure point, and the water flows through specially cast passages to the sides of the joint.
I have also seen confusion arise from the raw water/closed (fresh) water systems.
In a raw water cooling system, all of the engine (heads, block, manifolds) is cooled by sea water (or lake if you’re not in the sea) and flow through the engine, heads and into the manifolds then up to the elbows through ‘open’ gaskets.
In closed (fresh water) cooling the engine (heads, block, manifolds) is cooled by coolant that is cooled by sea water in a heat exchanger. The gaskets between the manifold and elbow (or riser if risers are being used) are closed, keeping the coolant in the manifold and separate for the sea water in the elbow.
The only exception is a ½ closed cooling system, where the heads and block have coolant and the exhaust manifolds have sea water, in which case you would want open gaskets.
The elbows themselves are also quite different and easy to identify by just a quick look.
Changing from raw to closed cooling does not change the system from wet to dry. To change from wet to dry, you need to replace the manifolds and elbows (and risers if you’re using them)… And you can't 'mix and match'. If you have dry joint manifolds, you MUST use dry joint elbows and risers. Conversely, wet joint manifolds can only have wet joint elbows and risers on them.
I hope this clears up the confusion.
As always, comments below if you have any. (And for the really experienced guys, this is a brief overview, an introduction, not a detailed explanation of every aspect of exhaust design. Yes I’m looking at you @Scott Danforth .
) If well received, I'll add it to the stickies.Chris....
Last edited:
