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

[cdre]

I am looking at buying a boat that originally had 2 Volvo I4 sterndrives that I want to replace with a pair of Mitsubishi 2.5L diesel engines. Trying to think of all of the major repowering obstacles, and one of the ones I was looking at was the exhaust. All of the sterndrives I have worked on have mixed the exhaust with cooling water enroute to the drive. What purpose does this serve? Can I get away with just fabricating custom exhasuts that rise post-turbo prior to exiting the transom directly? I know I will need some way to stop the sea water from coming back up, but I think most of the "performance" exhausts for 8cyl engines look like they do what I want my exhaust to do.

Think I am going to go for an enclosed cooling system with a raw water pump on the bracket where the a/c compressor once was.

In case you're wondering, these engines come from early 90's Mitsubishi Monteros (Pajero in the rest of the world). I live in Japan (Navy), and I am exporting these trucks and engines to Belize (where my father is from). Since these engines are pretty much electronics-free, there is one less obstacle.... and diesel is about 2/3 the price of gasoline in Belize... another big plus.

Any other recomendations/ideas are very welcome!

 

[cdre]

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

Doing a little more research, I have found that the water-cooled exhaust is more of a safety thing than anything else... enclosed spaces and all. I am thinking I would modify the existing through-drive exhaust to mix with the raw water discharge closer to the the drive itself. As for the heat of the exhaust manifolds, I am running diesel, so much less chance of a "flash" type fire, and I am thinking I would employ more than the usual number of bilge fans toward the rear of the compartment. Leaving the original radiator fans on the engines might help to disperse heat as well...

Thoughts?

 

[Bondo]

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

It Won't Work............

Water Cooled Exhaust is an Absolute Must Have,...... Period.......

 

[steelespike]

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

Absolute folly.You need water cooled manifolds that feed water to the exhaust system.
I have seen engines with dry exhaust but they were wide open with the exhaust pipe ending in open air.
Still damn dangerous.
Water cooled exhaust runs at something less than 200
degrees, dry exhaust I think something like 1200 degrees.

 

[JasonJ]

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

Plus, theres that small matter of turbos. Turbos build huge heat. You would have an extremely hot engine compartment. Unless you can somehow get safe water cooled exhaust at a reasonable cost, you would be looking at a custom exhaust system that would far outstrip the savings in fuel.

Repower should never be done for fuel savings alone, you never recoup the cost. It should be done because the original engine has suffer catastrophic failure. Cost-wise, you are best off just staying with what you have if they still run properly. What you propose is fine only if you have money to burn and just want to do it for kicks.

 

[steelespike]

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

If I'm not mistaken most marine engines are installed opposite of that in a car/truck.In other words the front of the engine faces the rear of the boat.There are no transmission attachment points for a transmission or I/O
assembly.And of course if installed the other way around
rotation would be wrong.Then there is the sump the oil pump may not be able to get oil in extreme hull positions.
sea action or bow rise.Then there is the electircal system even though it is diesel the electrical components are not designed for a marine application. and dampness may be a problem.As far as cooling the area you would need to move a huge amount of fresh air through the engine room Requiring large air intakes and exits.
And you would still have exhaust manifolds that would probably glow red under load.
Did you ever notice the heat build up in the cooling system of a car when it has been off for say 10 minutes or so and you turn the ignition on to note the engine temp.Imagine that trapped in a closed engine bay when you shut down after a nice long run at speed.

 

[cdre]

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

The original engines in this boat are shot, which is the reason I am looking at the repower. As they would be mounted to a sterndrive, the will face forward and will be mounted as level as they would in a truck (with the exception of course of pitch and rolls).

It would not be dificult to pull the turbo and pipe the exhaust directly from the manifolds to the drive, but I would still face the problem of a potentially hot exhaust. Thinking maybe I could bend the exhaust out of say 2.5" round, and bend a water chamber to fit around it from the point where it rises the most down to where it goes into the drive (an inch or so bigger in diameter). The two divided sections could then join and go into the drive's exhaust as normal. The manifold itself would still be hot, but I could wrap that in insulation and just keep the heat in mind when routing everything....

Feedback?

 

[Bondo]

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

Thinking maybe I could bend the exhaust out of say 2.5" round, and bend a water chamber to fit around it from the point where it rises the most down to where it goes into the drive (an inch or so bigger in diameter). The two divided sections could then join and go into the drive's exhaust as normal.
Feedback?

I'm guessing that you Haven't really Tried building a Water Jacketed Exhaust System before..................

It's not Quite as Easy as you make it out to be........
It would be an Extreme Challange,...
Even in a Very Well Equiped Metalworking Shop..........

Btw,........
Just How are you going to attach the Outdrive,..??..??...
Ya got a line on Mitsubishi, to Volvo adapters,..??.......

 

[DJ]

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

Marine engines face the same way as they do in rear drive vehicles. The marine bellhousing bolts to the rear of the engine.

Not only does the exhaust have to be cooled, so do the turbos. If not, they will coke up and fail very quickly, not to mention the safety factor.

Those engines in marine duty cycle are going to work allot harder than they ever did in a vehicle. Exhaust temps (behind turbo) could easily exceed 900 degrees F.

Since you are in Japan, I think I would look around and see if anyone ever marinized those engines. If so, the water jacketed turbos and manifolds may be avialable. Not cheap, I'm sure.

 

[cdre]

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

Good point on sourcing marinized parts in Japan.

One question regarding cooling the turbo... you mention that the turbo will "coke up." How is its operation independent of cooling different in this situation than it would be in a vehicle?

 

[steelespike]

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

Marine engines face the same way as they do in rear drive vehicles. The marine bellhousing bolts to the rear of the engine.

Not only does the exhaust have to be cooled, so do the turbos. If not, they will coke up and fail very quickly, not to mention the safety factor.

Those engines in marine duty cycle are going to work allot harder than they ever did in a vehicle. Exhaust temps (behind turbo) could easily exceed 900 degrees F.

Since you are in Japan, I think I would look around and see if anyone ever marinized those engines. If so, the water jacketed turbos and manifolds may be avialable. Not cheap, I'm sure.

Do all inboard marine engines face normally or just for I/O set up?I know that straight inboards used to be reversed.I suppose so they could have right hand rotation.?Number one cylinder was always at the transmission end of the inboard instalation.

 

[Buttanic]

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

Marine engines face the same way as they do in rear drive vehicles. The marine bellhousing bolts to the rear of the engine.

Not only does the exhaust have to be cooled, so do the turbos. If not, they will coke up and fail very quickly, not to mention the safety factor.



Those engines in marine duty cycle are going to work allot harder than they ever did in a vehicle. Exhaust temps (behind turbo) could easily exceed 900 degrees F.

Since you are in Japan, I think I would look around and see if anyone ever marinized those engines. If so, the water jacketed turbos and manifolds may be avialable. Not cheap, I'm sure.

Do all inboard marine engines face normally or just for I/O set up?I know that straight inboards used to be reversed.I suppose so they could have right hand rotation.?Number one cylinder was always at the transmission end of the inboard instalation.

I think you are referring to a V -drive setup where the V drive reverses the direction of the prop shaft. Just about all inboards face the engine forward.

 

[steelespike]

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

Not refering to V drive.I wasn't sure this morning but checked the normal rotation of automotive engine.If you sit in the car and observe the rotation of the crank;the top of the flywheel rotates to the left another words
left hand rotation.In a straight inboard if you install the motor with the flywheel to stern you will need a counterclockwise prop.left hand rotation.I've only worked on older straight inboards up to the early 60s.
All have their flywheel forward and number one plug at the transmission end.I don't know about I/O engines but
if the flywheel is forward with the starter present then they are in opposite of an automotive installation.
Anyone know about an I/O installation?
Sorry about the tangent but it may be relavent to the conversion being discussed nere.
Would be imbarassing to get the install all done and discover all was in reverse.

 

[Scaaty]

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

Drive is always off the rear bellhousing. Only V Drives to my (limited at times!) knowledge face the rear...

 

[steelespike]

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

If a straight drive is driven off the flywheel end of the engine it will be counter clockwise rotation.
In the picture it appears that is the timing gear cover facing to the rear.

 

[JasonJ]

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

There is a lot of air that moves through the engine compartment of a car. There is no moving air in the engine compartment of a boat. You would probably be more successful wit non-turbo charged diesel engines, but you would still have the headache of cooling the exhaust (and you would have a pair of gutless engines). Still, to pull this off you will be looking at dramatic cost. You could just rebuild the engines it has and be on the water for far less. Like I said before, you will never recoup the cost of what you propose with the fuel savings the diesels would provide.

 

[DJ]

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

What JasonJ said.

Turbo's in automotive applications are cooled by the engine oil and surrounding air. You don't have the latter, in a boat-usually.

Marine turbos also have a water jacket around them. "Coking" is the cooking of the oil once the engine stops. A very hot turbo would coke the oil that much faster.

 

[Buttanic]

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

Not refering to V drive.I wasn't sure this morning but checked the normal rotation of automotive engine.If you sit in the car and observe the rotation of the crank;the top of the flywheel rotates to the left another words
left hand rotation.In a straight inboard if you install the motor with the flywheel to stern you will need a counterclockwise prop.left hand rotation.I've only worked on older straight inboards up to the early 60s.
All have their flywheel forward and number one plug at the transmission end.I don't know about I/O engines but
if the flywheel is forward with the starter present then they are in opposite of an automotive installation.
Anyone know about an I/O installation?
Sorry about the tangent but it may be relavent to the conversion being discussed nere.
Would be imbarassing to get the install all done and discover all was in reverse.

I have a Chris Craft single straight inboard, the engine faces forward and rotates the same direction as a automotive engine. It has a left hand prop. As lonas the prop is correct and the rudder is positioned correctly for the direction of rotation it doesn't make a difference.

 

[Scaaty]

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

In the picture it appears that is the timing gear cover facing to the rear.

Of course...its a motor for a Vdrive drag boat. The V drive puts the prop back to normal rotation..

 

[cdre]

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

Ok, so I have a couple of ideas. For the exhaust, I am going to do some experimenting. First I will wrap it in copper tubing with raw water running through then overboard. I can run this test with the engine still in the front clip of the truck so I can get an idea of temps. If it cools sufficiently, I will weld in an inlet for the water to pass into the exhasut. Assuming that does not work (and I doubt it will), I am thinking I could have the same custom bent exhaust (very thick tubing) jacketed by just welding thick sheetmetal around it and putting in dividers to ensure the flow is correct (picture a big boxed in inverted "V" and an inverted "V" inside of the rise). After the rise and close to the transition from the custom exhaust to the outdrive connection, I would drill holes to allow the raw water to escape with the exhaust. I can check the effectiveness of all of this with an IR thermometer.

For the pre-turbo manifold, I would wrap with insulation tape.

Now, in an attempt to remedy the high air temps as a result of the confined space, I will keep the pre-existing fans on the engines. In front of them, I will mount the radiator's fan shroud on a chamber about 4 inches deep or so. This will allow the engine to draw in fresh air through a vent at the top of the shroud (about 2' off the cockpit deck). In the chamber, I would mount the intercooler that was previously in use on the truck. A few more vents on the rear to let engine heat/air escape, and I think I might have a manageable situation. 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.

Main reason for the big push for diesel is that I can get these engines for about US$800 each, and diesel fuel is about 60% the price of gasoline in the caribbean (where I will use the boat). I stand to save alot of money running diesel rather than rebuilding the gas engines.

So, thoughts on the exhaust/air-movement plan?