Manifolds

[glmoore001]

Ok, I have been lurking around here, reading posts. I know a little about machinery, auto and industrial, dont know crap about boats. What is it about marine inboard engine manifolds.

On cars they are never a problem to the point of being nonexistant, on boats they seem to be the largest problem of all. Why is that?

thanks..gm

 

[Alpheus]

Re: Manifolds

If not taken care of in salt water applications there are lots of places that they can rust out and leak. If these start to leak and water enters your engine it equals bad news.

 

[glmoore001]

Re: Manifolds

It still seems funny to me. First of all, how does that water get up to the manifold in the first place and could that problem not be solved by installing stainless headers or something to that effect? thanks...gary

 

[Stamey]

Re: Manifolds

Look at the bottom of the manifold in the pics. There are ports where water is force through. Typically the water goes through the water pump on the front of the engine, through the block, and thermostat, then into the bottom of the manifold and out through the elbow, pictured also, on top of the manifold.
The reason this is done is because there is not much air circulating around the engine, like a car, and so the exhaust manifolds would get very hot, likely causing a fire in the engine bay of a boat, so water is circulated around them to keep them cool.
The problem, which is worsened with salt water, is the water in the manifolds and elbows corrodes the inside of those parts and when the metal corrodes it expands and come apart, causing restrictions in the water flow, causing an overheat condition.
Stainless is a great idea, but besides being expensive, still is not forever. I was checking into that last week and when I searched I found people discussing their stainless manifolds lasting about 7 years, in salt water. Perhaps in fresh water they would last much longer, but I have not seen any discussions regarding that.
Stainless headers brings you to the same problem as auto manifolds, they need a lot of air around them to cool things off. The "headers" I have seen for boats are set in engine bays that are wide open, for air flow, and still have a port on them to spray water in to cool the exhaust gases.

Chris

 

[Simoniz]

Re: Manifolds

@Alpheus,

Great pictures, do you have any of the 3,0l manifold and riser?

 

[HT32BSX115]

Re: Manifolds

It still seems funny to me. First of all, how does that water get up to the manifold in the first place and could that problem not be solved by installing stainless headers or something to that effect? thanks...gary

Howdy,

You can buy SS manifolds for most engines. ($2000+ for a v-8) They still have to be jacketed though or they would get hot.....(VERY HOT)

The cast iron and aluminum manifolds are much cheaper.

Non jacketed "headers" or even cast iron automotive manifolds are not a problem on an exposed engine (with no engine compartment)

In an engine compartment NON-jacketed exhaust would quickly get so hot that you would have a fire or explosion (even if the engine ran long enough before it vapor-locked!!)

Jacketed manifolds with the right amount of water flow though them barely get hot enough to burn you (even if you hold your hand on them)

All the cooling water going to the engine (or heat exchanger if closed cooled) MUST be exhausted overboard through the riser/elbows. You have elbows to prevent the water from getting back into the exhaust either during normal running or immediately after engine shutdown.....


There's really no choice. In an enclosed engine compartment (which most all I/O boats have) you MUST use jacketed exhaust with some sort of riser.



Regards,


Rick

 

[glmoore001]

Re: Manifolds

It all makes sense now. I never thought about the heat from the exhaust causing problems. There is a lot more to this boat thang then I expected..thanks guys..gary

 

[singlesupra]

Re: Manifolds

Something is still confusing me here... on some of todays engines you get very little airflow to the engine and the manifolds still don't have a problem,even on turbo cars where the headers get
hot enough to turn red. Some coating and wrap and they are cool enough to touch.
It would be a simple task to install a few vents forairflow if needed. Justseems to me like running water through the header is a big pita way of addressing a simple fix, resulting in new problems

 

[singlesupra]

Re: Manifolds

Something is still confusing me here... on some of todays engines you get very little airflow to the engine and the manifolds still don't have a problem,even on turbo cars where the headers get
hot enough to turn red. Some coating and wrap and they are cool enough to touch.
It would be a simple task to install a few vents forairflow if needed. Justseems to me like running water through the header is a big pita way of addressing a simple fix, resulting in new problems

???

 

[Stamey]

Re: Manifolds

Fuel leaks.

If you're in your car and there is a fuel leak, causing a fire, you can pretty much just pull over and get out of the car. This is a bit harder on a boat, where you may not be able to see land, much less swim to it. Now, considering that, wouldn't you want it to be as safe and cool in that engine compartment as it can be?

Furthermore, in many boats the engine compartment is under some type of living area for people, and the extra heat that would permeate everything in the engine compartment would radiate up into the living area, making the people uncomfortable. As you probably know, the firewall on a car is thick, and sometimes insulated, to add to the comfort of the people inside, as well as to protect them from a fire.

Chris

 

[fishrdan]

Re: Manifolds

Something is still confusing me here...

Water cools the manifold, then dumps out the riser to cool the exhaust and everything downstream. Without water mixed in the exhaust it would burn out the; rubber shutters, rubber couplers, rubber seals. The drive wouldn't live a long life with 1000*+ exhaust flowing through it, it would cook the drive.

 

[Alpheus]

Re: Manifolds

Correct. Boats engines run hard like a truck pulling a 2 ton trailer up a hill at full throttle in first gear. Thats allot of heat.