headers

[brainsboy]

Why are the headers water cooled? Can you use car headers? The only reason I can think of, would be so that when the exhaust exits throught the haul, it doesnt burn the fiberglass, so why couldnt you just use auto headers then bend 3" tubing out the back and only water cool the section that exits the boat transom. This would be alot easier then trying to water cool each exhaust tube of the header.:P

[mmd]

Most boat motors have "open-system" engine cooling rather than "closed-system" (some form of heat exchanger such as a radiator & fan combo or a hull-mounted heat exchanger) to reduce weight and mechanical complexity. Basically, this involves picking up seawater from outside the hull, pumping it through the block to strip the engine heat away, then dumping it overboard. Since the exhaust manifolds need to be cooled to prevent fires in the engine compartment, it makes sense to use the engine block cooling water to do this job - two birds with one stone, so to speak. Because hot seawater is tremendously corrosive, it would eat ordinary car headers within a week. Therefore marine exhaust manifolds are made of heavy castings so they have a reasonable life span.

[gonzo]

Exhaust manifolds heat up to about 500 F. If you don't cool them there will be a fire hazard. Also, the engine compartment temperature will rise so much the engine will overheat.

[fcfc]

Not all exhaust manifold are water cooled.
First, for dry stack, I do not know.

Second, on deutz oil cooled engine, the exhaust manifold is neither water or oil cooled. But it is insulated. it helps increase the efficiency of the turbo and reduce back pressure in the exhaust.

It is all engineering choices, and each engineer may have a different set of parameter to optimize. engine cost ,installation cost, efficiency, thermal, noise, vibration , fashion/marketing , etc etc ...

[longliner45]

in the 80s alot of guys used pvc for wet exaust,alot of boats sank, dry exaust is good because its one less hole in the hull to worry about,,,,but the draw back is you need a muffler ,,for example my 471 detroit had a muffler the size of a 40 gallon barral, and once it caught fire 90 mi off shore,not good gentalmen make your choises accordingly ,if your on a lake for a few hrs a week ,wet is great ,never cut corners,dry has its pluses,,, again one less hole ,,,,,,,,,please pardon me for thowing this in ,,in my book porta pottis beat toilets any day,lot of sailboats and cruisers sink because of toilets,everyone on the back deck fishing or sunbathing whatever! the high water alarm goes off ,the capton looks at the engine rm first ,by the time he finds out whats happening he has 10000 gallon in the hull.all choises have consequence,,,,,,take that to the bank,longliner

[gonzo]

How does a dry exhaust avoid a hole in the hull? Also, where do you get the data about so many boats sinking in the 80's?

[longliner45]

hey gonzo how are you ?I was a commercial fisherman in the gulf of mexico for 10 yrs or so, the dry at least lets the exaust exit much higher than the wet exaust which is usually at or near the waterline.,,,as for data on boats sinking .it is from firsts hand expieriance ,there was a fishing bonaza in the 80s and for some reason a lot of boats used pvc for wet exaust,,,,,,,thier reasoning? I dont know.some boats sank because the pvc melted and was in a inconveint location under decks,probably ok at the waterline but not loaded.I can say I know of three comercial boats that sank,our sister boat broad bill 2 assisted one,as for toilets sinking boats I can only say I have heard of only one firsthand and 2 or 3 others secondhand Im just trying to be honest as I can ,as a gulf fisherman you hear whats going on in galveston while your in tampa,

[gonzo]

I can see that with a vertical stack. I know of at least four boats that sank from water siphoning through the toilet. These were sailboats with toilets below the waterline and the antisiphon valves were old and stuck shut.