Exhaust System Fabrication Questions

[Vince Luciani]

Hello everyone,

I am preparing to tackle my new exhaust system for my repower (Cummins 330's). I have decided that I want to go with the port crossover system using 4" diameter stainless. I have a good welder who is prepared to do all the fabrication/welding, however, he's looking for some direction from me. He's very compotent at welding stainless steel and is familiar with purging, etc., but he's never done one of these boat exhaust systems.

My question is regarding the riser at the end of the 4" stainless crossover. The Cummins provided riser (shower head) is not stainless, so I guess that can't be used. Any advice or tips on fabricating a stainless riser (shower head)? Should I even consider fabricating my own riser or should I purchase it and have my welder attach to the crossover piece?

I feel like the exhaust system is the last big hurdle for the repower project.

As always, thanks for the advice.

Vince

[In Memory of Vicroy]

Vince - the cupro-nickel sweep off the Cummins turbo is the ticket, then use some exhaust hose to isolate it from the stainless, then take the stainless where you need to go. But 4"? for 330s? You sure? I have 5" on my 250s and most use 6" on 300 and up.

UV

[Vince Luciani]

UV,

I'm talking about coming off the turbo with 4" stainless and crossing over the engine and then attaching the wet elbow. The exhaust hose will be 6" diameter after the wet elbow. Only dry exhaust will go thru the 4 " section. I've seen the setup on Tony Athens site.

[In Memory of Vicroy]

Vince, OK, understand, but you gonna have a very hot pipe you will need to heat blanket, not my favorite way to do it. My view is to cool the exhaust down right after the turbo then duct it out cool.

UV

[Bruce]

Vince,
While it is certainly acceptable to run the crossover as a hot pipe, you will need to make sure it is covered 100% or any little oil leak that hits that pipe will ignite.
The back of the 31 is a tight area including the distance to the engine box cover. Don't be surprised if it changes paint color from the heat.

I would not do it that way.
Here is a pic of the way I do the cummins. D'angelo exhaust in Ft Lauderdale has these.

I left the pic large so you can see detail. This engine is a 330hp. Size is 6".

[CaptPatrick]

Bruce,

One caveate here... That's with the Cabrera engine boxes... I don't think that one would work with the shorter stock engine boxes.

Br,

Patrick

[Vince Luciani]

Capt'n Pat,

You beat me to the punch! I really did want to get into the extended boxes. I like your setup Bruce but it won't fit in my situation. I understand your comment about the oil leaks and will take head. I can fit the crossover without extending my box.

What I'm interested in is the design of the wet elbow that would be attached after the "hot" pipe. Any input if I elect to fabricate these out of stainless.

[CaptPatrick]

Vince,

My recomendation would be to get, least the for the port side, the cross over from Tony Athens.

No offense intended to your local welder/fabricator, but if he hasn't built these units before, why should you be the guinea pig? This is a critical element and improper design and/or execution could be very costly...

Br,

Patrick

[Vince Luciani]

Thanks Capt Pat! That's the kind of advice I was looking for. I agree with you.

I was thinking that way myself, but that crossover is a high dollar item (+- $4500 quote for port and starboard), and I figured I ask about. At times, this repower project has given me "boat brain" (my term for mentally going around in circles) and you need input from others to set you straight. This forum is great for that.

My welder really wants to do one so that he could put it on his resume. I could probably save a couple thousand dollars if I went this route, but I don't want to be "penny wise, pound foolish".

[CaptPatrick]

My welder really wants to do one so that he could put it on his resume.

I can understand his eagerness and desires to add another notch to his TIG handle, but that's his selfish needs...

Once you have the real deal units, let him spend a day studying, making notes, & photographing them. Then he can make up a set to call his own for portfolio purposes. This way, you're Mister Nice Guy, he gets to practice on his own nickle, at his own pace, and work out his mistakes without a guinea pig being involved, (other than himself). He may even avoid a product liability problem before it happens. Win/Win...

Br,

Patrick

[Vince Luciani]

Capt Pat,

I totally agree. Thanks for the straight talk.

[scot]

Vince,

I understand your reluctance to spend $4500 for risers...when a hand full of practically off-the-shelf copper fittings lasted 40 years on you previous engines, with no problems!

Welcome to 2007. You could always go back with some more copper fittings, cover them with insulation and don't tell anyone....or post any pictures. I'm sure the fish won't know the difference and you'll still have $4300 in your bank account.

Good Luck

[Vince Luciani]

Scot,

I thought about it. But, I got too much $$$$ at stake with potential warranty issues if something were to go wrong. If the engines were 40 years old, I would certainly give it a try.

[Carl]

On my car I wrapped the headers with a high heat wrapping made for the application, I was wondering if it can or has been used for a dry crossover in place of the heat blankets?

I tried the stuff on the car so I could work around them without getting burnt, works real well as can touch wrapped pipes and heat in compartment is drastically cooler with the wraps on. I guess the big concern would be the wrap is cloth and the heat blankets I have seen look like they have a sealed outer surface keeping oil and contaminates out.

[Capt. Mike Holmes]

Bruce's picture shows a beautiful exhaust system, I don't see how it could be done any better. Put the wet exhaust elbow just after the turbo housing, don't run a hot pie over the engine where it can contact the engine box insulation. Remember, you have to take water off the raw water side of the heat exchanger to cool the exhaust, do it with as short a run as possible. I have "custom" fabricated exhaust elbows made of aircraft grade aluminum bronze that work great and will last longer than the factory cast iron units, but they come straight off the turbo housing.

Diesel exhaust is different than gas.

[scot]

Capt Mike,

Aluminum Bronze?? I haven't heard of this material being used for marine exhaust. I have seen it used in the industrial world for applications requiring a bronze type material, but with more strength. We used a bunch of it for the primary drive stem nuts in large motor operated valves. Tough enough to do the job, yet scarifical if the system failed.

Very interesting.

[Capt. Mike Holmes]

Scot, the guy who had mine made - in a qualified machine shop - was worried about the lifespan of the cast iron "factory" units. He had a friend at Bell Helicopter in Fort Worth who gave him the aluminum ronze formulation they used, and that's what he made these from. It was sort of experimental, I think I have the only ones. They are 5" on the exhaust side. The same gentleman made my exhaust manifolds, bellhousing, and intake manifolds out of aircraft grade aluminum - also a Bell formulation. He did extensive machining on the exhaust manifolds that was given an unofficial OK by the local Cummins people. The intake is split, because Cummins told him they had experienced air starvation to the back cylinders resulting in overheating, probably on higher horsepower engines. All this stuff has been in the boat about 6 years or so now, and I have yet to see a sign of any corrosion or weakness anywhere. The exhaust manifolds are light enough to carry in one hand. Much lighter than the cast iron versions Cummins uses. He also used oversized heat exchangers (copper), and my aftercoolers are basically the same size heat exchanger, with some modifications.