Ayrton Oneill
The exhaust manifold in a boat engine collects the exhaust gases from the engine's cylinders and directs them to the turbocharger, which uses the energy from the exhaust gases to spin a turbine. This spinning turbine then compresses the intake air, increasing the engine's power output. The exhaust manifold can be designed to bolt directly onto the turbocharger, or it may require some modifications, such as flipping the manifold around and mounting a turbo with a T4 flange. The heat generated by the turbocharger and exhaust manifold can be an issue, and some manifolds may require water cooling or upgraded radiators to handle the increased temperatures.
| Characteristics | Values |
|---|---|
| Purpose of exhaust manifold | Collects exhaust fumes generated from the engine during combustion of fuel and redirects it into the exhaust pipe |
| Purpose of turbo | Forces more air into the engine, increasing the strength of the combustion and producing more power |
| How exhaust manifold works | The exhaust comes out of each exhaust port and each port is run to an exhaust pipe and exhaust ran out the back |
| How turbo works | The exhaust from the cylinders spins the turbine, which is connected by a shaft to the compressor, which pumps air into the cylinders |
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What You'll Learn
Twin turbos on boat exhaust manifolds
I couldn't find much information on how boat exhaust manifolds work with turbos, but I did find some forum posts discussing the possibility of twin turbos on boat exhaust manifolds.
One user suggests that twin turbos could be mounted on a boat exhaust manifold with a T4 flange, but they would need to do more research. They also mention that they would likely need to run internal waste gates with these manifolds. Another user agrees that twin turbos could work with a T4 flange, but suggests that a T3/T4 hybrid turbo might be a better option. They also recommend plumbing the heater core hoses to circulate water through the manifolds to deal with the increased heat.
Some concerns are raised about the heat cycles that the manifolds would need to withstand. One user suggests that cast iron manifolds should be able to handle the heat, as cast iron cracks and melts above 1400 degrees. Another user questions whether the manifolds need to be cooled, as boat exhaust is typically only cooled due to the enclosed environment. They suggest filling the water jacket of the manifold with block filler if needed.
Overall, it seems that twin turbos on boat exhaust manifolds are possible, but there are some technical considerations to take into account, such as the type of flange, the need for internal waste gates, and the cooling of the manifolds.
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Mounting a turbo with a T4 flange
I couldn't find much information about how a boat exhaust manifold works with a turbo, but I did find some details about mounting a turbo with a T4 flange.
One user on a forum said that they were thinking of adding twin turbos to their formula and that they thought they would have to mount a turbo with a T4 flange. They thought it would be a direct bolt-on but would have to do more research. They also thought they would have to run internal waste gates with these manifolds. Another user replied that they couldn't see why they would need water, but one user suggested filling in the water jacket of the manifold with block filler if needed.
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Running internal waste gates
An internal wastegate is a built-in bypass valve and passage within the turbocharger housing which allows excess exhaust pressure to bypass the turbine into the downstream exhaust. Internal wastegates are designed into the turbine housing and generally have one or two pucks (a round piece of metal that acts like a valve) that block passages that are drilled or cast into the scroll of the turbine housing. When the pucks are closed, the exhaust flows around the scroll (the passage inside of the turbine housing) and through the turbine wheel like a non-wastegated unit. When the pucks are moved (or open), some exhaust will flow through the scroll and some will bypass the scroll and turbine wheel.
The bypassed exhaust is directed back into the main exhaust stream after the turbine wheel, but usually before or right at the down pipe. Control of the internal wastegate valve by a pressure signal from the intake manifold is identical to that of an external wastegate. Advantages include simpler and more compact installation, with no external wastegate piping. Additionally, all waste exhaust gases are automatically routed back into the catalytic converter and exhaust system. Many OEM turbochargers are of this type.
However, compared to an external wastegate, an internal wastegate has a limited ability to bleed off exhaust pressure due to the relatively small diameter of the internal bypass valve, and less efficient performance under boost conditions. To get more boost pressure (or delay opening the gate), installers can put more tension on the actuator rod by shortening the rods (either by physically cutting them down or by threading them down) which puts more strain on the internals of the regulator, but it does make the gate stay open later.
Internal and external wastegates work well when sized and positioned correctly. When setting up an internal wastegate, it is important to get the spring selection right based on your lowest and highest boost targets.
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$462.98
Heat cycles and cast iron manifolds
It is possible to add twin turbos to boat exhaust manifolds. The manifolds can be flipped around and mounted with a T4 flange, although one user suggests that a T3/T4 hybrid turbo would be a better option.
One user wonders whether the manifolds were designed for such extreme heat cycles, but another replies that they are made of cast iron, which can handle the heat. Cast iron cracks and melts at around 1400 degrees. The manifolds will reach around 1200 degrees without water, so the water jacket should be filled. However, one user points out that boat exhaust only needs to be cooled due to the enclosed environment, so water may not be necessary.
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Cooling boat exhausts
There are two types of exhaust systems: 'wet' and 'dry'. In a 'wet' system, engine cooling water is injected into the exhaust line, reducing the exhaust gas temperature to between 104°F-122°F (40°C- 50°C) and reducing diesel exhaust fumes. This is preferable to a 'dry' exhaust system, in which exhaust gas temperatures can reach 1,112°F (600°C) or more.
One example of a 'wet' exhaust system is the VETUS marine exhaust system. In this system, the cooling water is injected into the exhaust line, reducing the gas temperature and fumes. This system also transports raw water or seawater and protects the engine against water ingress.
Another way to cool boat exhausts is to use a lift muffler, such as a Centek Vernalift. These are vertical mufflers mounted below the waterline, with an outlet line coming off the top of the container. Exhaust gas and expended cooling water are mixed shortly after the exhaust manifold and travel together into the muffler's chamber, where the cooling water collects before the exhaust gas pressure pushes it out the remainder of the exhaust hose.
It is also important to consider the cooling water injection point. When this is less than 15cm above the waterline, the cooling system can siphon water through the intake when the engine is turned off. To prevent this, an air vent should be installed at least 40cm above the waterline.
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Frequently asked questions
Yes, twin turbos can be added to a boat exhaust manifold.
You can mount a turbo with a T4 flange by flipping the manifold around.
Boat exhausts need to be cooled due to the enclosed environment.
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