Diesel Wet Exhast Fabrication

I'm partway through my diesel engine installation on an old 24' cuddy sterndrive. Originally had 2 volvo sterndrive units. Had an adapter plate built to bolt bellhousings to rear of engines and fabbed up everything to connect shafts to outdrives...

One of the next pieces of the puzzle is the exhaust. These are Mitsubishi 4D56 turbodiesels out of trucks. My initial thought is to run a rise off of the turbo with a 180* bend at the top coming down to a sleeved "mixer" that will introduce raw water. Lets say roughly a 3" primary exhasut pipe with a 4" sleeve at the end for the mixer. Pipe would be T316 stainless.

My biggest question here, is how long does the sleeve need to run before it dumps into the exhaust? I can probably get away with as much as 12-14" but the examples I've seen online show relatively short sleeved sections, making me think length is not so important... Maybe I can get away with 6" or so...

Will this work? Any recomendations on tubing thickness?

 

Depends on the distance to the waterline. Also, if you run dry manifolds and riser, you need to put some kind of heat shielding.

 

length is not so important

 

Great... good info. Thanks! I figured insulation would be required on manifolds and the dry riser.

From the research I've done, it would appear that custom exhaust jobs are pretty common on diesel engines. Anyone know of a retailer that sells lots of these components? I could buy the tube and have things sleeved, drilled, and welded, but there might be some saved cost and improved quality buying a pre-fabbed mixer...

 

National Marine Exhaust, Marysville, WA, USA but there has to be someone closer!

 

If you use dry manifolds and risers, use heat shields mounted on spacers instead of insulation to reduce exhaust gas temperature.

The stainless mixer must be attached to the dry part of the exhaust system: you have dissimilar metals, sulfur and high temperatures there, so very favorable conditions for galvanic corrosion if raw water can reach that area.

Also pay attention to the inside diameter of the mixer. High exhaust gas speed tends to erode T316 when water is present, particularly if the flow meets an obstacle or a bend.

 

mark - I'm only in Iraq temporarily (uniformed) and I'll be in Norfolk early next year. Stateside suppliers are great!

Would heat shields on the manifold and insulation after the turbo be ok? This would keep EGTs down until the riser and help to minimize extra heat and noise in the engine compartment.

I was looking at doing the entire exhaust in T316. Not a huge expense since it is a small system. Was thinking to use .12" wall for inner and outer components of the sleeve at maybe 6" long with a 3/8 - 1/2 inch gap between the two tubes. Looking at .065" for riser and 180 pointing down to mixer.

 

First, Sir, thanks for what you are doing there. Private mail me if you might ever be in Alaska and I'll take you fishing.
"heat shields on the manifold and insulation after the turbo be ok" - That's how I'd do it. In fact, heat shielding the manifold wud only be for your personal burn protection unless the manifold is not water jacketed.
"heat shields mounted on spacers instead of insulation to reduce exhaust gas temperature" doesn't make sense to me. Safety and reducing engine room temperature are foremost in my eyes and a custom blanket does this well. I wudn't want to reduce EGT at the expense of higher engine room temps - most people feel that there is enuf turnover of air that it is not a consideration but forget (or never knew) that an engine at low RPM produces a lot of heat (particularly after a run) but doesn't use a lot of air. You can damage your engine with heat even after idling back... Reducing EGT is what the water injection does later in its circuit.
This national marine exhaust company doesn't have the best looking blankets in my view - there are, I'm sure, better companies for that and maybe the welding, as well. I live in the boonies so have to shop online for this stuff or fab it here. As far as thicknesses, There are others more qualified than I, perhaps CDK. I'd just ask my welder and accept his recommendation. The critical thing is to make the dry riser use as much of the engine room height as possible and don't inject water until well after the riser is coming back down. There shud be no way for a leaking mixer to get water in your engine.

 

Mark, I do recognize the need for a low engine room temperature because that is where the engines take their air from. I recommend large vents and a blower if necessary.
But I expect the manifolds to be gray cast. Packing them in a blanket will increase the temp to the point where cracks may appear. It also damages the gaskets between the water cooled head and the expanding/contracting insulated manifold. You don't want exhaust gas in you engine room unless you're a fan of EGR.

 

If I leave the manifolds open and wrap the riser to keep noise down, should I be OK?

 

Sure, the riser will be T316 which is quite flexible and heat resistant.

I am not familiar with Imperial tube sizes. Here in Europe 2 mm wall thickness is quite common for the diameters you need, but there is also what the Germans call "Gewinderohr" with approx 5 mm.

This is a small quantity supplier:
http://www.edelstahlrohre.info/shop/page/1?shop_param=

 

"I expect the manifolds to be gray cast..." - I have no idea but if they are not water jacketed, of course CDK is correct. I think you are on the road to a good exhaust system. Remember a port for your pyrometer and to have more or bigger holes in the top of the mixer than the bottom for the amount of waterflow the pump puts out - the idea is to encourage the water to not just drizzle out the bottom half of the "shower head" mixer. While you are doing this, remember, also, to weld on studs for an external heat sensor (this means buying the sensor now but you could just clamp a sensor on later instead of studs). The mixers properly run cool, so that if you ever lose water flow, this thing will spike in temp NOW and save your engine with an alarm. Get sensor set for about 160°F.

 

Talk to Mark at MESA he can help you with what ever you need. mesamarine.com

 

Another very good source of information and expertise is Tony Athens at Boat diesel.com.

http://boatdiesel.com/Articles/Articles.cfm?P=20070601_Introduction.cfm&Y=2007

 

The guru!