304 Schedule 10 or 40 for Exhaust

[JohnV8r]

Hey Guys,

Getting down to it. Need to know whether I need:

1. Schedule 10 or Schedule 40

2. 304 or 316 stainless pipe

for the dry exhaust between the engine and the exhaust mixing elbow.

Thanks in advance!

Johnv8r

[Carl]

316L is the preferred, followed by 316 and 304 last

[Carl]

That goes more so for the filler being used as the welds are the 1st areas to see problems

[Carl]

Schedule 40 is very heavy for exhaust. If you use, make sure to add supports to carry the weight instead of hanging off turbo.

[bob lico]

i use 316L SS schedule 10 with zero problems in 16 years.

[scenarioL113]

John

Make sure you study all the info you can before you start welding. Numerous guys right here on this site have excellent designed exhaust systems. You can search on the seaboardmarine forum as well and their website for marine exhaust systems and ideas.

It is important to design a system that is NOT "doomed to fail". When you are on the seaboard (sbmar) website you can prob search those words "doomed to fail" and you will get plenty of info on what NOT to do.

"Up and Over" the top is a good design and is pretty straight forward setup. You just need to place the mixing elbow in an area where it is aiming straight down (if you can or close)... I think Bob L has info on that if you search this forum...


...anyway good luck and post pics of course

[JohnV8r]

Frank,

Thanks for that. Yes, I have read Tony Athen's articles on exhaust systems. I think I have a fairly cogent plan that includes surge tubes and risers, but I don't think I'm going to add a tee to allow water to bleed off overboard as Tony Athens suggests. I have read everything I can find here, but have not read that anyone here has installed that type of water bleed to relieve pressure Tony Athen's suggests. I think I have designed the exhaust so there should not be any pressure issues, and more importantly any chances for water to travel up in the exhaust and into the engines. If I've missed something, feel free to speak up now.

I made these exhaust pieces that are 4" upright Vernatube pieces that the mixing elbows will connect to with a Shields silicon bellows. The 4" Vernatube pieces will be trimmed down once have the engines hung in place so the water entry point from the mixing elbow is as low and far away from the turbo as possible. The 4" pieces are going into 5" Vernatube so I don't have to worry about back pressure on the 84 degree entry angle from the 4" to 5" connection. I used 5" so I can use my existing Vernatone mufflers.



When I replaced my deck, I put 6" exhaust from back of the muffler to the custom through hulls I glassed in. That leaves me with a relatively short run on the 5" exhaust of 20" + the muffler (38.5") before it opens up to 6".



Here are the mixing elbows I had made. I left plenty of length on the top to trim and/or create a minor angle adjustment coming in from the dry side:





Based on the sum of Bob Lico and Carl's recommendations, I have ordered 316L Schedule 10 pipe with the same long radius 45 degree elbows. I ordered extra 45 degree elbows to ensure I can take the exhaust as high as possible under the motor box hatches.

I also bought a pair of these 6" pipe pressure test pieces to keep birds from nesting in my exhaust while I am out of the water. I may use these as an extra precaution at anchor or during the winter when I might get some kind of surge into the exhaust.



If there is something I'm missing here, now's the time to chime in. I do appreciate all the feedback!

Thanks,

JohnV8r

[Carl]

John, I don't recall if you went Cummins 6BT or with the Hyundai's.

In either case exhaust looks great.

I believe the idea of the water bleed was when you Do Not have enough Exhaust Diameter to keep the back pressure down.

If 6BT-
4" with 6BT's is ok, till you add a muffler and they recommend 5". You are 5" after the mix, right? If so your there, no need to bleed off water to reduce pressure.

[Tony Meola]

Carl

I think John has a Turbo so maybe 6BTA and if 250 to 270 HP he can get by with 5 inch exhaust. Those are 5 inch coming off the engine.

[Carl]

I thought I read John had 4" going into the 5" veratone muffler then 6" to the transom

[JohnV8r]

Hi Guys,

I went with the Hyundai Seasall S270's. I'll put a post up on why later.

My exhaust starting from the turbo will be 316L Schedule 10 stainless steel 2" to the mixing elbow which then comes out at 4". From the wet end of the mixing elbow, there will be approximately 10" of 4" exhaust including the bellows off the mixing elbow. That 4" exhaust does an 84 degree connection to the 5" Vernatube which has a 10" surge tube on one end and the exhaust on the other. That piece (pictured above) then connects to my original 5" Vernatube muffler. On the backside of the muffler is a Vernatube "reducer" that takes the exhaust to 6".

This is an old photo from 2018 when I test fitted the exhaust when I replaced the deck, fuel tank, and put in custom fish boxes. You can see where the exhaust changes to 6" on the backside of the muffler. From this photo just figure everything from the front of the muffler that is horizontal is 5". The vertical piece that will connect the mixing elbow is 4".



Hope that gives a better visual.

JohnV8r

[JohnV8r]

One other thing real quick while I'm thinking about it.

I love the original Vernatube mufflers and the good job they do. I remember Bob stating in a post some time ago that he wasn't thrilled with the straight mufflers he put on Resolute. I always thought after that I would keep the original Vernatube mufflers if I repowered.

However, I had a minor exhaust leak for a couple of years somewhere before I pulled my deck off. Capt Patrick told me once in a phone call that the only place the original Vernatube mufflers could fail is at the seams where the two ends attach to the round middle piece. He told me if they were going to leak, that was the place (unless they had a hole in them). To keep this short, I pressure tested mine by capping one end and filling the muffler with water while standing it up. I did in fact have a leak in one of those seams.

I faired and glassed the seams on both mufflers. Pressure tested them again. Painted them and reinstalled them when I put the new deck in. It's like they're brand new.

Thanks,

JohnV8r

[Carl]

Hi Guys,

I went with the Hyundai Seasall S270's. I'll put a post up on why later.

JohnV8r

Why...because you thought they were the best decision for your needs. Best of luck with them.

The Cummins motors are real sensitive to back pressure and it has to be kept low. That is not the case for all motors, my buddy has 240 Yanmars in his Albamarle, his factory exhaust would not be adequate for my old 440 gas motors, never mind my 6Bt's.

What is the permissible back pressure allowed on your motors? I'd assume the recommended diameters and runs are stated in the motor manual. Use that over what we know as it may not be what you need. Although the basic design stays the same and seems quite good.


My old veretone mufflers leaked at the hose fitting. Prior stewart must have snugged up the clamps a bit much cracking the fitting. He loaded it and the hose up with silicone. It was fine till I changed exhaust manifolds disturbing the seal. I pulled muffler, glassed the crack, a quick grind and was good till the day I pulled it all some 20+ years later. I guess its common as they make crush sleeves for them.

[Tony Meola]

John

It looks like you ran the exhaust down the outside alley. I did not think those 5-inch mufflers would fit. I remember others going with the low profile Veratones.

[Snipe]

John I purchased all my 316 pipe schedule 10 from https://pipingnow.com/