Why install a Wet Manifold?

[rjohnbriggs]

I would like some thoughts here regarding the possibility of eliminating the wet manifold for a four cylinder diesel (Isuzu c240).

The wet manifold appears to fulfill two primary design functions. First, provide a surge volume and cap for your coolant system. This could easily be done using much cheaper components.

The second function would be to reduce engine room temperature. This is something I am familiar with. The wet manifold does little to cool the exhaust gas. That is accomplished where your raw water is sprayed into the exhaust riser. The surface area of the exhaust manifold is very small, and could easily be wrapped with ceramic fiber tape just like your exhaust riser. This would reduce the temperature somewhat.

I can understand the need for a wet manifold if you have a very small engine compartment, but mine is large, and easily vented. I called the coast guard, and they stated that if they boarded my boat, they would not look for any engine features such as a wet manifold.

I may be missing some design detail here, but in my case it seems that the expense of the wet manifold is not justified. Any thoughts?

[PowerTech]

I have actualy seen a izusu powerd generator that was keel cooled in a shrimp boat that had a dry manifold.It had a dry stack though I bet you could stick a wet elbo on it and it would work.If you are comfortable with any fire hazard from the dry manifold go for it.It is not sweat or nice but it will not hurt engine function.Dang shure cheaper.

[FAST FRED]

One advantage is the water cooled is quieter than the cast iron auto version.

A really nice powered vent systen should keep the engine compartment temps (hopefully below 100F ) at rational levels.

FAST FRED

[mari.larry]

Have seen fordson diesel with half inch copper pipe wrapped around all the inlets and exit of cast manifold. Guess it sucks up a bit of heat .Not sure if it was used to preheat the raw water before entering the block.

[FAST FRED]

This could also have been a Po Boy method of getting hot domestic water .

FAST FRED

[tom kane]

On of the bad aspects of wet exhaust manifolds is that the pulsing of the exhaust drives sea water back against the valve seats,this of course makes the valves rusty and liable to stick.A wet,hot,salty, steamy exhaust is not a good environment.

[gonzo]

No it doesn't. Only a badly designed system or a leaky exhaust valve would cause that.
Dry stacks are used in commercial boats. However they are much hotter which can cause a fire and power loss too.

[tom kane]

Hi Gonzo,You did tell us previously,that marine engines did not use oxygen sensors because they could not distinguish between steam and oxygen.You can stop to a limited degree the exhaust pulses driving water back against the exhaust valves,but marine engines do not have that idea incorporated.Pulsing in induction and exhaust systems is a fact of life.If you install a dry exhaust it would be sensible to insulate or water jacket the hot exhaust,and if you wanted to quieten the exhaust noise,inject water at the tail pipe.

[stevel]

I think the original post is asking about the exact opposite. No water jacket, but injecting water into the exhaust gas.

[gonzo]

The location of the oxigen sensor is very critical to its functioning. It needs a fairly high temperature to operate, which a wet exhaust negates. Also, it needs to be far enough from the exhaust ports so it reads the average exhaust mixture. This works out to about 12-20" from the head. An engine with a dry stack can use oxigen sensors. However, that would also mean reconfiguring an ECU for marine use.

[tom kane]

High temperatures are normal in dry exhaust systems.A dry exhaust in a boat or auto would not necessarily lead to the need of altering a ECU or preferably using an after market Programmable Engine Management System.No moisture in an exhaust should be best.

[tom kane]

Originally Posted by gonzo

No it doesn't. Only a badly designed system or a leaky exhaust valve would cause that.
Dry stacks are used in commercial boats. However they are much hotter which can cause a fire and power loss too.

No water in a wet exhaust would soon stop you with burned out plastic/rubber parts as used in some wet exhausts,leading to a fire,a dry insulated/water jacketed all metal exhaust with a closed cooling heat exchanger/radiator would not have that problem.

[PowerTech]

Tom do you even know what a boat looks like?Wet exhaust is the best in a plesure boat or yacht.It is safe and clean.You dont have a big pipe and crap running throught the cabbin.There is no problem with eather system when intaled corectly though.It is used on comertial boats because its simple and cheap.When they have a keel cooler and a dry stack they have cut down on alot of posible trouble also.I am talking about diesel engines.I dont know what they do for gas dry stacks..(((No water in a wet exhaust would soon stop you with burned out plastic/rubber parts as used in some wet exhausts.)))Come on now he dont meen no water in a wet exhaust he meens no water on the inside dry part except if its instaled wrong.

[tom kane]

We know what the advantages and dis-advantages of wet and dry exhausts are.I prefer to combine the two together.An all metal insulated/water jacketed manifold with a metal wet tail pipe (with anti-polution scrubbers) which has no problems running dry.Closed motor water cooling which does not rely on raw water cooling so it can be run any where,any time.

[Carioca]

Tom Kane wrote:

An all metal insulated/water jacketed manifold with a metal wet tail pipe (with anti-polution scrubbers) which has no problems running dry.Closed motor water cooling which does not rely on raw water cooling so it can be run any where,any time.

A promising solution , with the added advantage of not stealing any power if the original automotive engine is turbo-charged (cooling the exhaust charge that feeds the turbo entails lowering available power output by at least 5%, if not 10%).

Now take a modern automotive diesel, for example, the likes of VM Motori´s 200HP V-6 (Italy) and the new tandem-turbo International Engines (USA) 200 HP V-6. Both have EGR (exhaust-gas-recirculation) cooling for emission reduction.

How would a metal-shroud/water-jacketing arrangement over the exhaust manifold affect the ECU set-up , as the (shrouded) exhaust manifold gas temperatures would tend to be higher than the design value ?

Even if there were no EGR, say, just a standard mechanical-injection diesel. What is the downside of using a metal-shroud/water-jacketing solution ?