Engine exhausts and water intake

Designs for inboard or outboard power

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Tony Hain
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Joined: Fri Aug 26, 2011 3:01 pm
Location: Queensland Australia

Engine exhausts and water intake

Post by Tony Hain » Sun Apr 21, 2019 3:40 pm

So do I have this right?
1.You do not reduce your engine exhaust diameter. So if your motor has a 4 inch exhaust outlet then your exhaust system will be 4 inch all the way through.
2. You increase you water intake. So if your intake is 1 1/4 inch then your water pick up will be 1 1/2 inch.
Tony Hain
"Never under-estimate the bounds of human stupidity" (Robert Heinlein)
and on a more optimistic note "nor the capacity for human brilliance"

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Roberta
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Re: Engine exhausts and water intake

Post by Roberta » Sun Apr 21, 2019 4:03 pm

That's what I did on the Torpedo. Everything works fine.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Tony Hain
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Joined: Fri Aug 26, 2011 3:01 pm
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Re: Engine exhausts and water intake

Post by Tony Hain » Sun Apr 21, 2019 6:17 pm

That is what I thought. Thanks Roberta.
Tony Hain
"Never under-estimate the bounds of human stupidity" (Robert Heinlein)
and on a more optimistic note "nor the capacity for human brilliance"

TomB
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Re: Engine exhausts and water intake

Post by TomB » Sun Apr 21, 2019 7:08 pm

Tony,

I don't think it is quite that simple. There is an engineered amount of cooling water required and a maximum acceptable amount of back pressure. Both can be radically affected by a convoluted piping system.

I've seen 30 gpm (114lpm) listed on a similar 5.7l engine(Crusader) for cooling. Water pulled through the inlet, seacock, elbows, strainer, interior surface of the pipe all generate flow restrictions. You are probably ok with 1 1/4" throughout the system. Like Roberta, I am going with 1 1/2" from inlet through the strainer, then I am reducing to 1 1/4" straight hose the last 3'. I see several 1 1/4" systems on the forum and in the gallery.

On the exhaust side, I think you have a 3 1/2" exhaust elbow if you have a PCM EX343. In addition the convoluted piping, puddles in the pipe can also cause unwanted back pressure and condensation that may find its way into the engine. Crusader says 4" diameter, single or double exhaust for the 5.7l and has requirements about minimum pipe slope and minimum height between the top of the above the waterline for the top of the exhaust elbow. I am just getting to this point myself and I'm considering two options, 3 1/2" for everything or 3 1/2" to the muffler and then increase to 4" for a side exhaust. I wouldn't consider reducing the exhaust pipe diameter as there is too much risk of having to do it over.

Tom

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Roberta
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Re: Engine exhausts and water intake

Post by Roberta » Mon Apr 22, 2019 5:07 am

I used 4" for the entire exhaust. The black parts are 4" Centex Ski Mufflers. They have two crescent shaped baffles in them. The system has a nice slope to it to keep out water. There are flappers on the exhaust outlets, but after losing one, I took the other off because they are noisy as they clatter quite loudly. The elbows are Stainless Steel and positioned nicely to direct the exhaust out.

The intake piping is 1-1/2" off the 1-1/2" inlet strainer. The seacock is 1-1/2" with a 1-1/4" hose nipple. The hose to the strainer and to the engine is 1-1/4" and there is a 1-1/4" flushing Tee between the seacock and strainer.

This setup has worked fine for 5 seasons in all temperatures encountered while boating.

Roberta
Attachments
exhaust system 012.JPG
exhaust system 011.JPG
intake piping 002.JPG
Strainer 002.JPG
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

Tony Hain
Posts: 360
Joined: Fri Aug 26, 2011 3:01 pm
Location: Queensland Australia

Re: Engine exhausts and water intake

Post by Tony Hain » Wed Apr 24, 2019 1:09 pm

The PCM with catalytic convertor has only a single exhaust outlet. I still want 2 exhaust ports for symmetry. Might be a bit obsessive / compulsive. Any reason I can't put in a divider in the exhaust line? Any thing I need to consider?
Tony Hain
"Never under-estimate the bounds of human stupidity" (Robert Heinlein)
and on a more optimistic note "nor the capacity for human brilliance"

TomB
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Location: Holland, MI

Re: Engine exhausts and water intake

Post by TomB » Wed Apr 24, 2019 3:24 pm

Tony,

Wye'd together for the catalyst, why not wye back apart, seems reasonable to me.

I received the beginnings of my exhaust today, the muffler. It is basically a 6" dia. x 36" long fiberglass tube with a few baffles in it that will lie athwartship. Engine exhaust comes in from the side of the tube and "quiet" exhaust goes out the ends of the tube. So, like you, I will be mingling the exhaust streams before putting it out through dual exhausts.

Tom

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hoodman
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Re: Engine exhausts and water intake

Post by hoodman » Thu Apr 25, 2019 1:34 pm

I've seen video where an H or crossover pipe in a dual exhaust system showed an improvement in horsepower.
Matt

Building a Geronimo......!
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Tony Hain
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Joined: Fri Aug 26, 2011 3:01 pm
Location: Queensland Australia

Re: Engine exhausts and water intake

Post by Tony Hain » Thu Apr 25, 2019 6:38 pm

Thanks folks for your replies. I guess I will make a final decision when I drop in the motor. Did a test fit and had to cut away a frame for the sump but the motor should be lower than the hatch which was one of my concerns. Making up reinforcement for the cut away frame and working on the engine mounts.
Tony Hain
"Never under-estimate the bounds of human stupidity" (Robert Heinlein)
and on a more optimistic note "nor the capacity for human brilliance"

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