New repowering project... does exhaust really need to be cooled?

[cdre]

Re: New repowering project... does exhaust really need to be cooled?

And regarding attachment of the outdrive, I do not have any special adapters... I will cut the bellhousing of the transmission about 4 inches or so away from the engine (retaining the starter mount). I will fabricate a mount to connect the cut bellhousing to the transom mount. For the flywheel, I will have it machined to accept the original drive plate. Both of the forward engine mounts will obviously need to be fabricated as well.

 

[cdre]

Re: New repowering project... does exhaust really need to be cooled?

Also... I need to work on that rank... Cadet was almost 10 years ago... and then, it was Midshipman...

(some feedback for the mods... Cadet is an Army term... Midshipmen is Naval Academy.... then again, the Coasties use the term cadet as well, so I guess it could go both ways... but wouldn't you rather be DOD than DHS?)

 

[DJ]

Re: New repowering project... does exhaust really need to be cooled?

The turbos might get hot, but they shouldn't get hotter than they would on a truck. Fuel line connections would be wrapped in a lagging material similar to that used on bigger ships to prevent atomization/fires.

Oh they will get hot alright. Boat engines never coast. They are under full load all the time. Your only saving grace may be to let the engines idle for an extended period before shutting them down. That may cool the turbos down-somewhat.

Good luck.

As for I/O engines, they are no different than base automotive (except marinization parts) engines as to the way they mount. The I/O bell housing bolts onto the rear of the engine just as an automotive transmission would.

V-drives (like the picture) reverse the engine in the boat but the bell housing still bolts to the back of the engine.

 

[JasonJ]

Re: New repowering project... does exhaust really need to be cooled?

One additional thing to do. The turbos are cooled with the engine oil, so if you are going to build that chamber for the intercoolers, you will want to mount up the largest oil coolers you can get. This will help with keeping the bearings from overheating in the turbos. Anything that can be done to keep the turbos cool will help you tremendously. Connecting the engines to the drives will not be a problem, that is easily overcome with machines adaptors. Front engine mounts are the easiest part of the project.

If you can get the exhaust cooling issue ironed out, You will be in okay shape.

 

[sport15]

Re: New repowering project... does exhaust really need to be cooled?

Thoughts:

For years there have been BOTH types of turbos, water cooled and non water cooled. The non water cooled in most applications run hot and are designed that way. The safety concern is getting/being burned by them if you come into contact with them. ISUZU and others solved this problem by putting a blanket (lagged/fireproof) over them and the turbos did just fine with a cool down at the end of the day. Anyone who runs hard then shuts down without any cool down for any engine is asking for trouble. The coking of the turbo happens in the bearing housing when the residual oil gets baked by a really hot turbo that has been shut down without a cool down and results in plugged up oil passages resulting turbo failure right when you don’t want it. So dry tubos are not a new thing in marine application and Mitsubishi may have stats for you on the recommended operating temperature of the turbos.

You are not blazing new ground, Google Mitsubishi marnie conversions and see what you get.

Dry exhaust is not a new thing either. There is almost an even split up this way between wet and dry systems. The dry guys say that there is no way that they will pay for the fancy plumbing and have the chance they will pump thier boats full of water in the event of a failure. The wet guys say that they don’t want a pipe coming up through the platform and out of the boat and don’t want the noise. When I was lobstering (with a dry exhaust) as a kid we would heat cans of soup on the exhaust manifold for lunch and would grab on to the lagging on the exhaust stack to warm our hands while were hauling gear. Lots of ways to build a boat..

If you have access to stainless pipe, you can fab up an inverted sink trap (riser) and have the warmest of your cooling water injected into the exhaust line down hill/stream of the riser to cool things off and then send the mix down and out through the outdrive. Take a look at how the after market folks do it to get some ideas.

The fan on the front of the engine for a marine application is a new one on me and I don’t really understand why you would need or want to do that. The cooling system setup for the boat should be sized so that it will keep the block the temp it needs to be for the water temp that it will operate in (big difference between the Sea of Japan and Carribiean?). This means is that the heat exchanger on a closed system has to be big enough and the external water pump sized correctly. Any marine retailer that sells these parts should have a chart that will swag the size you need for the horsepower that you are operating.

For a water pump look at:
http://www.jabsco.com/prodInfoApp/s...MFPD&page=0&catalogId=Marine&categoryId=JMFLX

For a heat exchanger go to:
http://www.sen-dure.com/Marine.asp

and look for the catalog tab. It is a 3.5mb .pdf

Sheet in sailor and Damn the torpedos !!

Regards, Dave

 

[Frankenrude]

Re: New repowering project... does exhaust really need to be cooled?

OK so I am brand spanking new here 8) - but this thread made me join. Since I didn't catch this in anybody's response Her are my thoughts on the original question.

The exhaust MUST be cooled by active jetting. A jacket on the pipe won't do squat. Insulate your manifold & it will melt. You would be better off supercharging than with turbo. DO NOT run hot exhaust gasses into the lower unit exhaust passage unless you like the idea of melting the L/U housing. Also - if the original engines were gasoline - the gear ratios of the lower units will likely be way off for the Diesel engines you propose. You need to repower for reliability, safety and serviceability. Anything else is pure foolishness. Sorry if I sound crass - but this is a serious re fit & it should only be done correctly.

 

[Mark42]

Re: New repowering project... does exhaust really need to be cooled?

- - - The exhaust MUST be cooled by active jetting. A jacket on the pipe won't do squat. Insulate your manifold & it will melt. - - -

I agree with Frankenrude on this. The cooling affect of a copper coil with water will just cool the surface of the pipe, not the hot gasses inside. Wrapping the manifold will just allow the exhaust to stay hotter farther down the pipe.

You want to cool the exhaust gasses, not just the manifold.

 

[sport15]

Re: New repowering project... does exhaust really need to be cooled?

Google or Ask will be your friend..

The point about the gears is good. It is easy to get the ratio ## and then change as needed. The Mitsubishi is going to turn slower by a bit then the gas motor did and will most likely require a different wheel as well.

The tubing wrap will probably not give you the heat transfer that you need and even if your time is cheap you may be better off finding stock stuff. There are a number of after market bolt on manifolds that are available you just need to find one that will match the exhaust pattern of the engine. Check out: http://www.diecon.com.au/index.html they might have all your answers.

If you really don’t want to do this you can shoot the exhaust out through a hole in the transom that has been properly insulated, possibly not so good an idea if it is done to high up it will be sooty and noisy. You would still need a goose neck/riser to prevent water from getting sucked in at the wrong time.

Many years ago we were loading building supplies onto a Harris 36 lobster boat that had a wet exhaust (engine was a Detroit 671N) that went out the stern below the platform. As the load increased the exhaust was buried, at the time it was no big deal because the engine was idling.. We started to complain about the constant bath of spray and the good Captain shut down the engine. There was a sudden lowed CLANG as the engine came to a stop. Inspection revealed a bent connecting rod on #6 piston.. No riser had been installed when the boat was built. So, when the engine overhaul was complete a brand new huge stovepipe size dry exhaust came up through the platform just aft of the house next to the mast. The stack was double piped from just below deck level to about 3 feet above the flange where it came up though the platform to keep things (boat/crew) from getting burned.

When the boat was re powered with a Detroit J&T 671TI the dry exhaust was used and the turbo was lagged. Nothing ever melted, and this boat was raced and won fastest in it’s class 3 years in a row.. There is NOTHING like the sound of an unsilenced 671 running hard at 2550, yes 2550.. (give you a @#$%!! headache that lasts for two days!)


Good luck..

 

[JasonJ]

Re: New repowering project... does exhaust really need to be cooled?

It is doubtful he is going to find a lot of gearing options, he will probably have to overcome the gearing issues with pitch/diameter changes on the props.

 

[wire2]

Re: New repowering project... does exhaust really need to be cooled?

Ok, my experience as relative to this thread;

I have an '84 Glastron 19' that had a 5.7/OMC (260 hp) new. I wanted to lessen the total weight, so replaced the cast iron intake manifold with a Holley aluminum one, (60 lbs to 14 lbs).

Then discovered that the exhaust manifolds were 55 lbs per side. I got lots of stainless tube elbows and fabricated a pair of double wall headers, (18 lbs per side).
I also replaced the cast pipes to the mid drive with 1/8" aluminum tube, (.5 lb each)

The headers are 1-3/4" inside and 2" outside, they rise and converge in a 4 into 1, 3" and 3.5", then elbow back down towards the transom. The inner 3" tube stops 10" down from the riser elbow, where the cooling water in the jacket is allowed to flow with the exhaust. Similar to OEM.
A Y section allows thru hull or down to the mid drive/prop with a butterfly valve operated by a small vacuum cylinder, dash controlled.
The cooling is quite effective, even after a hard run, I can put a bare hand anywhere on the system.
The jacket is supplied by the original water connections from the thermostat block on the engine, split into 4 each side and feeding in very close to the heads.

The headers took a lot of hours to make but well worth it in terms of performance. I also added a slightly higher cam and 1.6 roller rockers.
It comes up on plane in less than 1 second, tops out at 58 mph with a 21" prop. I will put a 23" on it soon to bring rpm's down from 5500. But it sounds SO cool!