Exhaust system size

[ndutton]

We started talking about increasing the size of exhaust systems over on the troubleshooting section so I thought I'd move the discussion over here.

The more I think about larger aqualift exhaust systems on our little engines and their ability to expel water, the less I like 'em.

As an example, the difference between the cross sectional areas of 1 5/8" exhaust hose and 2" exhaust hose is about 50%. In terms of exhaust gases, going bigger reduces backpressure allowing the engine to breathe better. No quarrel from me.

In terms of expelling water though (the whole purpose of an aqualift system), it takes a greater volume of water to 'seal' off the exhaust hose so the exhaust pressure will push it along, especially push it up. Also, there's less exhaust velocity to do the job with a larger system. We need to factor in how much exhaust force we have available in the first place, most critically at idle. In sort of a twisted way, I can see where a larger exhaust line could result in more backpressure when factoring in the added volume of water in each 'batch' as the aqualift system batches out the water.

I'm sure there's a sweet spot somewhere between too small a system and one too large. We have pretty good historical data given the number of A4's with aqualift systems but I'm not sold on the 'bigger is better' strategy. The fact we're dealing with wet exhaust systems changes things.

Thoughts??

[hanleyclifford]

Neil - I guess you knew that I would be among the first to respond to this new thread. I like the way you have framed the issue. Let me begin by saying that I have been using 2" ID pipes and hoses all the way to the transom for several years. But your discussion about "diminishing returns" is sound and should give reason for pause about going any larger. The engine must always be able to expel the water. This requirement of course is going to vary with each boat's configuration. The greater the "head" against which the engine is working, the more dangerous larger wet sections would be potentially. All this of course needs to be quantified. Just one final thought for now: the manifold exit diameter is 1 1/2" - comments on why the manufacturer would reduce immediately to 1 1/4"?

[Dave Neptune]

I pretty much agree with you both about the additionl preassure and or "flow" to force the water out up & over and so on. However after the water is injected the exhaust gasses will cool rapidly and require less diameter than an exhaust system without water injection and we still need to evacuate the water through the same crossection.

Perhaps the exhaust back preassure guage will give some answers as to how the A-4 responds to back preassure. Many engines due to there cam profiles require a bit of back preassuure to "breath" properly under load conditions.

I actually have two riser hoses so to speak, I take it up under the cockpit then back down to the bilge then up to the transom. Lotsa pipe and hose maybe 14~15 feet or more.

Dave Neptune

[hanleyclifford]

Dave - I think as we move forward in this discussion it might be useful to post some exhaust system pictures. We have seen quite a few Catalina 30 pix. I would like to study your "twin risers". Attached is a view of my hot section. 4000 hrs on this configuration.

[rigspelt]

I like Hanley's two 90s and one 45, but can't arrange that in our boat. Ended up going with the design it had when I bought the boat, after much head-scratching and research, except for more height in the dry stack, adding height to the red coolant line (added antisiphon valve in the red hose later -- this photo was taken during dry-fitting) and shortening the exhaust hose run to the transom. Haven't measured the back pressure, but seems to run just fine, with no seawater backup threat. After running the engine, there is about an inch of water in the muffler. Boat's level waterline is just below the top of the muffler.

[hanleyclifford]

Rigspelt - Nice neat set up. Are we looking at the MM aqualift unit? I like the fact that you appear to have your injection point about a foot above the water line. One of the weaknesses of my system is that I inject just about at the line. For this reason I am obsessive compulsive about shutting off the thru hull every time I shut down the engine - even at a refueling stop! Regards, Hanley

[67c&ccorv]

Originally Posted by hanleyclifford

Neil - I guess you knew that I would be among the first to respond to this new thread. I like the way you have framed the issue. Let me begin by saying that I have been using 2" ID pipes and hoses all the way to the transom for several years. But your discussion about "diminishing returns" is sound and should give reason for pause about going any larger. The engine must always be able to expel the water. This requirement of course is going to vary with each boat's configuration. The greater the "head" against which the engine is working, the more dangerous larger wet sections would be potentially. All this of course needs to be quantified. Just one final thought for now: the manifold exit diameter is 1 1/2" - comments on why the manufacturer would reduce immediately to 1 1/4"?

Hanley...I'm thinking that 1 1/4" shedule 40 pipe was the largest inside diamter Universal could machine threads in the manifold pipe bracket without having to recast a much larger part that would accomadate a Schedule 40 1 1/2" (or larger?) pipe.

[hanleyclifford]

Originally Posted by 67c&ccorv

[/B]


Hanley...I'm thinking that 1 1/4" shedule 40 pipe was the largest inside diamter Universal could machine threads in the manifold pipe bracket without having to recast a much larger part that would accomadate a Schedule 40 1 1/2" (or larger?) pipe.

I opened up a stock flange to 1 1/2" NPT and ran it to Florida and back twice before I made my own custom unit out of 1" steel. The performance improvement was notable. I have never understood why Universal would take a manifold with a 1 1/2" outlet and immediately chop off a third of the exhaust flow by going to a 1 1/4" flange. Does not compute in my limited mind.

[67c&ccorv]

Spent some time at the boat yesterday cutting out the aft section of my Corvette's exhaust system.

It was a 10' section of 1 1/4" bronze pipe with all connections and changes of direction welded!

Old school engineering done very well...probably should have left it in except it was very heavy and took up a lot of space. No provision (other than an upward bend in the pipe at the transom) to keep following seas from flooding the system.

It also appeared to be very sound with little or no deterioration in the I/D of the pipe...except for the soot which is all over me and the boat now!

Now I have a MMI waterlift at the transom with a 2" bronze swing checkvalve in the outlet line.

Pics to follow when I get a chance.

[67c&ccorv]

Originally Posted by 67c&ccorv

Spent some time at the boat yesterday cutting out the aft section of my Corvette's exhaust system.

It was a 10' section of 1 1/4" bronze pipe with all connections and changes of direction welded!

Old school engineering done very well...probably should have left it in except it was very heavy and took up a lot of space. No provision (other than an upward bend in the pipe at the transom) to keep following seas from flooding the system.

It also appeared to be very sound with little or no deterioration in the I/D of the pipe...except for the soot which is all over me and the boat now!

Now I have a MMI waterlift at the transom with a 2" bronze swing checkvalve in the outlet line.

Pics to follow when I get a chance.

Hope these pics can help you understand my exhaust system - now if only I had a proper video cam to show the exhaust batching and initial startup with little water coming out the transom!

1.) from the exhaust manifold end showing the initial cooling water inlet into the water jacket exhaust;

2.) the business end of the water jacket showing the cooling water exit which follows along top of the exhaust gas 1 5/8" line to the transom;

3.) looking down on the exhaust gas and cooling water lines which enter the MMI S/S waterlift muffler under the lazarette and then exit through 2" swinging check valve and overboard at the transom;

4.) 2" line from the check valve to overboard at the transom;

5.) transom view of 2" S/S thru-hull.

Cheers!

[romantic comedy]

Originally Posted by hanleyclifford

I opened up a stock flange to 1 1/2" NPT and ran it to Florida and back twice before I made my own custom unit out of 1" steel. The performance improvement was notable. I have never understood why Universal would take a manifold with a 1 1/2" outlet and immediately chop off a third of the exhaust flow by going to a 1 1/4" flange. Does not compute in my limited mind.

Can you tell us about the performance improvement?

[hanleyclifford]

Originally Posted by romantic comedy

Can you tell us about the performance improvement?

Sorry to say I have no quantified proof. My exhaust hot section back pressure is 1 psi or less and the hesitation on throttling up disappeared. MM sells a lift with 2" output, so I reason why not increase the input side of the lift as well? It's the "batching" issue that limits output size, and I still have slight batching at cruise. I suppose I should have documented my journey from 1 1/4" thru 1 1/2" to 2", but I didn't.

[Dave Neptune]

Guys, I've been trying to attach a drawing of my exhaust and when I check the "prieview" it is huge! How do I reduce the image so I don't screw it up?

Anyone?

Dave Neptune

[lat 64]

I don't know what you have for software.
If you have a camera then you probably have a disc with some limited photo editing software. Fire it up and look for settings that are good for resizing for e-mail., that's what you want.
You could e-mail it and I'll copy it and resize it for you for now 'til you learn how.


Update: Right on Shawn

[sastanley]

lat64 - great idea creating an e-mail address with L/L coordinates! Be careful leaving that link active for too long though, as I think the Google bots search this forum and cache that stuff and then spammers can get it...may want to change it to all text similar to this: 64n147w at gmail dot com.

Dave, Another quick & Dirty answer - If you are using MS Windows, open it in "Paint" and choose Image>>Stretch/skew and then set both vertical & horizontal to some percentage (make them the same number!!) that makes it reasonable..(try 50%???) - Then save the file with a new name.

Eventually, you'll find a size that works.

I personally have a Microsoft Powertoy called "Image resizer" installed which allows me to right click on the file directly (right from the camera card) and re-size it to 1024 x 768 (or smaller).

Alternatively, I also have installed a free program called Paint.NET which is much more powerful than MS Paint, and has a resizing option built right in from the menu.

[Kelly]

Hanley,

I'll have to measure when I get back down to the boat. If I were to guess at the inner pipe diameter (hot section), I would say 1 1/4". I'll get back to you...

67,

As drawn in your schematic, our exhaust systems are nearly identical, with only small differences in the angled connections. It would be interesting to know if someone removed the mixer (riser?) from your setup. This would, I assume, as in Russ' example, eliminate almost all back pressure.

[67c&ccorv]

Originally Posted by Kelly

Hanley,

I'll have to measure when I get back down to the boat. If I were to guess at the inner pipe diameter (hot section), I would say 1 1/4". I'll get back to you...

67,

As drawn in your schematic, our exhaust systems are nearly identical, with only small differences in the angled connections. It would be interesting to know if someone removed the mixer (riser?) from your setup. This would, I assume, as in Russ' example, eliminate almost all back pressure.

This winter I plan to do maintainence in that area - once I pull off the insulation I will take some pictures. My copper-jacket exhaust extends almost to the rear of my cockpit - much longer than the blueprint.

There is a heck of a lot of water in it when I drain the thing for winter storage!

[tartansailboat]

I just noticed a leak in my exhaust system, good time for a question. My Tartan 30 has the MM SS water lift muffler, works great. I have a horizontal 1 1/4 inch nipple out of the manifold followed by a 45 deg elbow down, then a water injection fitting then about 12 inches down to the water lift muffler. No riser and not much of a vertical drop but it work well, never had a problem. I want to replace the nipple with a 316L SS nipple from Mc Master Carr, pretty cheap at about $10 but they offer two wall thicknesses, sch. 40 and Sch. 80. The schl .80 should outlast me but I would suffer about 10% loss in area, is that a problem??

[sailbristol]

my bristol has a copper jacketed pipe 11/4 id for the exhaust, the water doesnt enter the system till the very end at the down turn of the pipe to the fitting in the transom. no water back up problems at all just can't figure out how they put the bends in the two pipes and still leave a space between them for the water to run

[sailbristol]

my bristol has a copper jacketed pipe 11/4 id for the exhaust, the water doesnt enter the system till the very end at the down turn of the pipe to the fitting in the transom. no water back up problems at all just can't figure out how they put the bends in the two pipes and still leave a space between them for the water to run

[Boat]

hey all, I've been reading this thread and you all have pipe comming out of the engine. My motor has a westerbeke manifold type thing with the raw water going into that then down to the water lift. then 2" hose out to the transom. it's fairly new. my motor was rebuilt by a company in British Columbia. All of the motor pics i have seen here doesn't have it. I really like it, i have no reason not to. I'm just wondering why the pipe instead of the... (I don't know what to call it.) part I have

[blhickson]

How do you measure an exhaust system if its connected, operating and covered with heatwrap? How do you measure backpressure? Thanks. Just curious for possible future reference.

[Dave Neptune]

Barbara, the pressure is measured with a gage mounted into the "exhaust flange" if the flange has a tapped hole for doing so.

The more common and messy way is to unhook the exhaust and run it for a few seconds to test for better power and or RPM's.

Dave Neptune

[hanleyclifford]

http://www.moyermarine.com/images/cylhdman1.jpg When you do a new exhaust riser the Moyer flange has the pressure port built in.

[hanleyclifford]

The rest of the kit from Moyer Marine for testing back pressure: