DRY-JOINT EXHAUST...
What is Dry-Joint Exhaust? Skip to examples of Dry-Joint Exhaust
Dry-Joint Exhaust is an innovative exhaust system featured on all Mercruiser V6 and V8 models through 425 horsepower, dry-joint exhaust systems virtually eliminate the opportunity for water, either from condensation or from seawater, to find its way into critical engine components.
| While externally the V6 and small-block V8 systems appear very similar to previous designs, the real new technology is hidden inside. The internal geometry is totally new and was developed using computer-aided modeling to contour the surfaces, reducing exhaust restriction while ensuring precise temperature control of crucial areas. Take a look at the results in the illustration to the right. |
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Notice Those Two Red Rings? Those are special 4-lip
high temperature silicone seals that secure the coolant flow between the exhaust
manifold and the elbow. Check out the distance between those seals and the
large open area where the exhaust flows. There's no way that coolant can
find its way into the engine here. Those seals are mated to an engineered
GrafoilŪ gasket that is made up of a stainless steel core bonded to a special
graphite material that provides a precision high temperature seal for the
exhaust gases. The cone that you see on the gasket around the large
opening is called a "turbulator ring". Its job is to help catch any small
droplets of water condensation that may collect downstream in the exhaust system
that try to find their way back to the engine, where they can wreak havoc on
internal engine parts. You might say: "Condensation! That means
water! If the exhaust system is so well-sealed, where does that come
from?"
Here's the answer - water in the exhaust of a marine engine can come from two
sources: one is the water that exits the engine through the exhaust system
to help reduce the temperature of the exhaust gases and the exhaust system.
The water also works to help reduce the noise level of the exhaust. The
other source of water is the water created from complete combustion. Yes,
water is a product of combustion and can condense on the inside of the exhaust
system when the inside surface temperatures are not high enough to evaporate it.
So, these exhaust manifolds and elbows are designed to run at higher
temperatures on the inside, while still staying as cool as possible on the
outside. There are still times when condensation could form, like when the
engine is warming up or when operating in very cold water for long periods at
idle. The "turbulator ring" is for that extra margin of insurance.
