Exhaust Riser Drawings

[Marshall Mahoney]

Does anybody have drawings for exhaust risers on their Cummins?

[scenarioL113]

If you search on sbmar.com you will see many custom exhaust designs for Cummins engines.
search the word "exhaust" and "doomed to fail". This will show you what NOT to do.

The most important thing is to create a "hump" in the system which can be done directly off the turbo and the mixing elbow or straight fitting (depending on how you configure it). The mixing fitting will be downward from the hump and preferably in a "straight down" position before it straightens out to find its way towards the transom.

The hump would just be stainless steel pipe 5" or 6" directly connected to the turbo. This hump would need a "turbo blanket" or multiple wraps of heat tape cloth but once the mixing elbow comes into play the rest of the system does not need the blanket.

The factory Cummins wet elbow is rarely used in the custom exhausts that you will see out there.

The new way is to create a "trap" to prevent the seawater from finding its way into the turbo... Unfortunately the "doomed to fail" scenario is the way boats have come delivered brand new for years...GOTO SBMAR.COM

[Marshall Mahoney]

Thanks -- I am familiar with Sboard and the theory of design. Just seeing if someone had drawing to give me an easier place to start. I am looking to have them fabricated locally -- not purchase them. I have a lot of blowby in both of my engines. There is a good chance that I have had water back up into the engines over the years. When I have them re-built, I would like to add risers.

[Carl]

To get my design I bought aluminum dryer vent hose and mocked up.

Make it fit, check your clearance, and connections, remove and it holds its shape. Now you have something to measure.

It comes in sizes relatively the same diameter of tubing, the bends formed are very close to standard off the shelf tube bends.

[Marshall Mahoney]

Dryer hose -- I like it. I found a picture of your starboard elbow on the bench. Did you post pics of starboard and port risers installed before insulation?

[Carl]

I thought I did, I’ll have to check and see if I have others.

[Carl]

As my port box is right up to the riser I slathered some high temp silicone (good to 600 degrees wrap was just under 200) over making it quite touchable...leave a hand on and you know it's hot, but that's about it. Down side is its not pretty. The starboard side needed an additional pass or two with the wrap. I bought blankets, but with insulation, I put on I am happy with temps...maybe as it ages some I'll change, modify or...

[JeremyD]

I wonder if you could design this using Silicone Hose.

[Snipe]

It is pretty easy to fabricate the exhaust I did buy the mixing heads from seaboard marine they weren’t cheap but definitely made the job easier!

[Marshall Mahoney]

Thanks guys -- these are really great pics. 5" ID pipe would be ideal for my 300 HP but harder to come by. Now I need to figure out how to open my wallet.

[Snipe]

https://pipingnow.com/pipe/
This is where I got all pipe and elbows.

[Marshall Mahoney]

Y'alls engines are so pretty and white -- so weird.
Jason -- it looks like you have a 3" x 4" reducing elbow coming out of your turbo, then the rest of your pipe is 4" correct? Also -- what is your HP?

[bob lico]

almost exactly mine but i rotated 90 degree fittings to use 70 degree at bottom. 4" ID out of turbo is perfect iand 6" wet pipe for 330 ,370 hp cummins any more than 4" ID on the hot pipe and you lose on volumetric efficiency .

[Marshall Mahoney]

Bob-- not sure what you mean by "volumetric efficiency" -- those are some mighty big words. You are saying that 4" is plenty for the hot piping in a 300HP? Seaboard seems to indicate 5" but he mentions 4" as well. 4" is certainly cheaper and easier to route than 5".
No issues with 316L for the mixing elbow? It seams that hot salt water is a pretty severe service (stress corrosion cracking). Sounds like that is what everybody is using.

[Tony Meola]

Marshall

More than I bet you want to know.

https://help.summitracing.com/app/answe ... y-%28ve%29

You have to remember Bob is speaking in Racing World terms. Something most of us are not worried about unless you are going for the ultimate results from an engine.

Bob has done a heck of a job squeezing every ounce of power and fuel efficiency he could out of his engines.

[Marshall Mahoney]

If Bob says 4" hot pipe will work, I am good with that. In fact, I am very happy with that...
Guys -- thanks for all of your input. Got to love Bertram31.com!