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Author Topic: What to make generator exhaust stack out of?  (Read 8934 times)
Kevin Warnock
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« on: January 11, 2010, 06:18:51 PM »

First, thanks for the rain flap idea in my other post today about how to keep rain water out of the vertical exhaust pipe for my Honda EU1000i generator install.

Now I wonder if anyone has some input on what material to use to make the exhaust stack from.

I don't yet know how to weld, but I want to learn. Not sure if I should be learning on something so critical to life though.

So I was thinking about using galvanized water pipe from the plumbing supply store. The generator is in the front doorway of the bus, and I want to exhaust just behind the drivers seat in the center of the walkway, left to right. I want to exhaust up front so as to keep the generator noise as far from the back bedrooms as possible.

The plan would be to run the galvanized pipe up the inside of the wall that separates the drivers' area from the living area, which is right behind the drivers' seat. Then when the pipe gets to the ceiling, go almost but not quite horizontal for about 18" along the top of the interior residential door frame that is used to access the living area of the bus. Then make a 90" turn and go right out the center of the bus, about 3 feet back from the front windshield.

Not sure if it's OK to put two sharp bends in an exhaust system. The Honda exhaust port on the generator as it comes from the store is about 3/8" in diameter. That's the exit size of the muffler. I was thinking about removing that muffler completely and discarding it, in favor of a car muffler. The appeal of this approach is the exhaust exit from the engine is flat and has two bolts protruding from the engine block to hold the muffler. This gives me a solid place to attach my exhaust pipe. If I leave the stock muffler, I have the problem of how to make a tight seal around the flimsy sheet metal 'exhaust pipe' that is only about 1/8" in length. No room for even a hose clamp on it.

I suspect if I use a larger diameter exhaust pipe for the approximately 10 foot run to the top of the bus that the engine will tolerate the pipe bends.

If I use a car muffler, where's the best place for it? In the sound box itself? In the wall? Will any car muffler work, or should I look for a certain style?

I was thinking about using 1" diameter galvanized pipe with furnace cement as a high heat 'pipe dope' for the threads to make it air tight.

I was thinking about wrapping the exhaust in some kind of heat resistant wrap like I've seen in bus engine compartments. Not sure what product to use. Does this sound reasonable?

The bus will have spray foam insulation in the walls and ceiling, so I need to control heat so I don't burn down the bus. If needed, I can maintain a safe separation of several inches between the exhaust and the foam. I could substitute rock wool insulation in this void, and presumably I can put rock wool right up against a hot exhaust pipe?

Remember, the generator is just 1000 watts, so it's not making that much exhaust compared to a big generator. Not that it should matter, but the generator is already converted to run on LPG.

Thanks very much!
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luvrbus
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« Reply #1 on: January 11, 2010, 08:07:39 PM »

use electric metal conduit and have someone bend it for you or go to a pawn shop and buy a bender I paid 5 bucks for mine, water pipe is to heavy and cost more


good luck
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belfert
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« Reply #2 on: January 11, 2010, 08:59:16 PM »

If you go to 1" why not have a muffler shop bend up what you need.

I would check with Honda to make sure this will really work.  I'm not sure the engine will like that long of a continuous exhaust pipe.  The genturi type stacks are open at the bottom so they won't interfere with engine operation, but that won't work for inside a vehicle.
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« Reply #3 on: January 11, 2010, 09:22:52 PM »

I agree with belfert, I think that from the front of the bus to the back then 10' is way too much pipe for such a small engine.

Run it directly out the side  and make a detachable, two-piece, vertical stack for use when parked. I plan to do just that very soon. Going down the road it won't matter to exhaust out the side. I do this.
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cody
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« Reply #4 on: January 11, 2010, 09:39:04 PM »

I've got the honda 3000 inverter, the big brother of your generator, when I approached the dealer on running a additional pipe or muffler to channel the exhaust I was told by the guy that it would work out great for him if I did because the engine wouldn't last very long without the prescribed back pressure, he's an old mechanic that carries the honda line and is kinda well versed in them, I bought my 1965 honda 150 dream from him new, cost me 560 bucks brand new lol, so he's been around a long time and seems to know a lot about honda, whether he's right or not, I don't know.  I've got my honda strapped down in the a/c compartment back by the engine, the door of the a/c compartment is one big grill and I've got a box fan strapped to the top corner of the door and it's plugged into the generator exhausting outward, when the generator is running, the fan is exhausting.
« Last Edit: January 11, 2010, 09:43:21 PM by cody » Logged
RJ
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« Reply #5 on: January 12, 2010, 01:22:50 AM »

 

The generator is in the front doorway of the bus, and I want to exhaust just behind the drivers seat in the center of the walkway, left to right.


Huh  Shocked  Huh

I'm having a hard time wrapping my head around the idea of a carbon monoxide-producing generator in the front doorway of an MC-5a running at night. . .  Might be the last time somebody goes to sleep!

Please elaborate or post a photo?

FWIW & HTH. . .

 Wink

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RJ Long
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Van
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« Reply #6 on: January 12, 2010, 07:11:11 AM »

I thought the Honda's were quiet? Huh Or is this one in Question a beast Undecided
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Kevin Warnock
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« Reply #7 on: January 12, 2010, 01:00:16 PM »

Whoops, sorry. My first bus was a 1967 MCI5a. The new one I am converting from a passenger bus is a 1994 RTS 40'. The front door way where the stairs are is where the generator will be, in a box sealed from the living area under the new floor I'm building there. In effect, the generator is in a storage bay that happens to be one I built, not original. The box and the new floor will be well sealed. All routine entry and exit to the bus is by the rear door. The passenger seat will sit above the generator in the front stairs area. In an emergency, the front door can still be opened and people can jump out.

To be clear, I was planning the exhaust pipe to be 10' total in length. The exhaust will go out the front roof of the bus, not the back of the bus.

If the engine can't handle a 10 foot exhaust, how do generators handle the exhaust extensions to the top of RVs that Camping World sells? Those look about 8 - 10 feet high. Remember, I am planning to use 1" diameter pipe where the stock exhaust on the Honda is about 3/8" in diameter. The area of a 1" pipe is much larger than a 3/8" pipe, which is why I thought it would be OK. But maybe the engine counts on having a particular amount of resistance? If so, there must be a way to calculate how much resistance would be provided by pipes of various lengths and diameters. Does anyone know of a calculator or of the formula? I don't want to harm my engine.

Yes the little Honda is quiet, but I am just trying to do all I can to not be disturbed when sleeping and running the AC off the Honda. It will be a 5000 btu window unit that draws 500 watts so it will run fine from the 900 watt Honda. The AC will start on the Honda alone per my tests. But there will be a Trace SW4024 in between the Honda and the AC, so I will have lots of starting power. I will use the Trace control panel to set the Trace to draw 500 watts at night. This has the great effect of slowing down the Honda engine to about half its full speed, making it even quieter. I've even considered telling the Trace to draw 300 watts, which forces the Honda to its idle speed where it's the most quiet. Then the AC can cycle on an off normally, and when running, draw 200 watts AC from the battery bank and when not running, the 300 watts from the Honda can be used to charge the batteries. This might result in the batteries being at the same state of charge in the morning than they were in the evening even though the AC was running from them partly during the night.

Thanks
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bevans6
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« Reply #8 on: January 12, 2010, 01:25:25 PM »

The thing about the backpressure is that the "extensions" that camping world sells and others copy (Gen-turi, if you want to google it) is that they have a complete disconnect between the stock exhaust pipe and the upright, and they use a venturi effect to draw in cool air at the bottom and use the heating effect to pull the exhaust up, just as a fireplace chimney does.  The gen engine only sees it's stock exhaust.  You could do a very similar thing by having a short extension from your exhaust out the side, and an add-on bit that is the genturi equivalent.  I have a Yamaha 3000 installed in my old AC bay, the predominant "sound" is from vibration, not exhaust noise.  I built a 1.5" header for it that extends down to below the floor and out the side.  I was concerned with backpressure as well, and I used the transition from 1/2" (the muffler output) to 1.5" to reduce the back pressure effect.  At the end of the day, you'll have to try it and see what happens.  I can about guarantee that Honda won't warranty the generator with a modified exhaust. 

I make headers for race cars, lately I have been buying bends from these guys:  spdexhaust.com  smooth flowing bends have virtually no effect on back pressure, btw. 

Brian
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gus
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« Reply #9 on: January 12, 2010, 06:57:12 PM »

It should handle 10' total with no problem  but you still need to check the installation manual because it will answer your question. My Honda manual was very specific about that. I thought you were going to run it out the rear roof!!

There seems to be some confusion about back pressure, the longer the pipe the more the back pressure. Back pressure is good for a long stroke slow turning engine but bad for a short stroke fast turner. This is the reason race cars use headers and trucks don't.

I don't agree that the open venturi exhaust extensions relieve back pressure, if anything they increase it. If this were true big trucks would use this system. The suction of the venturi is powered by the exhaust just as a venturi water pump is powered by water pressure in a hose.

The only reason I can see for the bottom opening on the extension is for cooling the vertical pipe. Cooling a vertical exhaust pipe also increases back pressure because hot gases will exhaust faster than cooler gases. I don't plan to have my vertical extension open at the bottom for that reason.

Same goes for your home chimney. Cooler gas up the chimney decreases the draw of the chimney and also causes crud to collect in the chimney.
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cody
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« Reply #10 on: January 12, 2010, 07:29:11 PM »

I really don't know what a person could expect from it, all I know about it is when I talked to my honda dealer he said that the engine wouldn't last if I did that, and the warrenty would be voided, he said he has worked on several that had mufflers changed, lengthened, pipes added etc and each one had gone bad in short order, he said honda engines are very unforgiving of any alterations like that, since he has been a honda dealer/mechanic since the mid 60's I took his word and didn't alter mine.
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buswarrior
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« Reply #11 on: January 13, 2010, 07:49:58 PM »

Do I remember something bad about heating galvanized metal?

How hot will be bad for off-gassing something harmful?

happy coaching!
buswarrior
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« Reply #12 on: January 13, 2010, 08:26:13 PM »

What I did: My exhaust stack.
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« Reply #13 on: January 14, 2010, 04:57:36 PM »

BO,

I give up, what is EMT pipe?
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belfert
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« Reply #14 on: January 14, 2010, 05:45:53 PM »

EMT conduit/pipe is the metal conduit used for electrical wiring.  I'm sure you have seen it in many commercial buildings running exposed.  You probably just don't know the proper name.
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« Reply #15 on: January 15, 2010, 07:17:56 AM »

When we were starting the conversion of BigBus, I insisted that Larry figure out a way to exhaust the generator through the roof. 

Of the generator, he used a flexible exhaust hose, used a union to tie it to the stack, then extended exhaust pipe on up through the floor and roof.  We used a 4" double wall flue pipe (hvac people of course) as a "chase".  At the floor, we mounted a double wall flue pipe collar on the bottom and on the top side of the floor, extending the flue pipe on down through the floor about an 1" below floor level.  This gave us a "thimble" of sorts to keep the floor from getting hot. 

We ran the flue pipe on up and terminated it just flush with the top sheetmetal on the roof.  We used homemade "keepers" to keep the generator exhaust pipe centered in that chase.  The exhaust pipe continued on up through the center of the chase and terminated about 8" or so above the roof.  So, if you're picturing this, you'd see that we have free airflow from the generator compartment, around that exhaust pipe, all the way up and through the roof.

The last thing was to figure out a way to keep rain from coming back down the pipe.  Larry built a flashing out of a flat piece of aluminum, with a hole cut in the center, and riveted a tubular shaped piece (with bendable tabs cut in the bottom to insert down through the hold of the flashing and bend back underneath it) to that flashing, then sealed the seam.  This sealed the hole in the roof, and now we've got a small round tube sticking up, with a smaller exhaust pipe sticking through it.  All we needed then was a cap.

Again, we had to fabricate it, so he bought two curved tips and welded the small one to the exhaust pipe, and used a larger one, cutting tabe and bending them in to meet the smaller one, fashing a rounded top basically to come up against the center one.  It's hard to explain, but he ended up with a stepped cap. . .  maybe 3" or so on the wider portion, curving down and attached to a 1 1/2" center one.  . .  welded to the exhaust pipe sticking up.  The wider 3" portion slid down over the flashing sticking up through the roof so that the flashing was sticking up between the outer portion of that cap and the inner exhaust pipe.  Once we slid it down, we supported the exhaust stack at the bottom so that the cap did not touch the roof and there was just a little gap between the top of the flashing and the inside rounded portion of the cap.  Does this make any sense?Huh
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« Reply #16 on: January 15, 2010, 08:23:46 AM »

I too have a transit (AMGeneral 10240B).  I installed a 10kw Powertech Diesel generator next to the front seat like a front engine-facing backwards so the lower part of the gen is tucked under the dash.  The reason- I have 3 roof top A/C's for my only A/C system.  With 2.25" of sprayed insulation, two A/C's running while driving in 108 degree weather (hottest I've been in) will keep the interior at a comfortable 75 degrees.  Turn all three on and my wife puts on a sweater. Also, the only propane I have (I really dislike propane) is the stove and furnace.  So with mostly all electrical including two 10gal water heaters, electric heat in the bathroom, 2500 watt inverter with two 8D's, a 6.3 cu Norcold AC/DC refer and a Norcold AC/DC 2.1 cu chest freezer, microwave, toaster oven, washer/dryer, I can truly use the 10kw of the generator.
Personally, I don't quite see how you're going to get along with a measly 1kw worth of electricity-unless everything is propane and your only electric A/C is that small 5,000btu window unit.  How do you stay cool in summertime?  Still have the over the road A/C?  Good Luck, TomC
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cody
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« Reply #17 on: January 15, 2010, 08:32:48 AM »

I guess the question I would have is would the run affect the operation or longevity of the generator, we have to realize here that the generator in question would pretty much fit in a bread box and has an exhaust slightly larger than the diameter if a pencil.  The honda 1000 is very small in size.  When you feed the puff, puff of that small an engine into that size of a pipe and run it that far what is the long term and would it be detrimental, my initial gut feeling is that it may hurt the generator, the dealer supports that idea and says the warrenty would be voided, I'm sure an alternate method could be worked out, I understand that the cost of the generator isn't huge at less than a grand but to someone like me a grand is a lot right now. This isn't a 10 or 15 HP diesel generator were talking about, this one is easily picked up and carried around with one hand.
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Van
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« Reply #18 on: January 15, 2010, 09:24:17 AM »

Right, it's not a big gen set, so why all the fuss in trying to make it quieter? Ours is a 5.5 onan)(CCK type) and that thing will wake the dead, of course with nothing but the header pipe Shocked. Yesterday I picked up a 10 foot section of EMT( 7 bucs @ true value) a 90 elbow ( 3 bucs ) and some couplers and we are all set to be nice neghbors Cheesy. Spent a total of 25 dollars and this will do the job nicely, if not I can always turn up the tunes to drown out the generator LOL! Grin Grin Grin
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cody
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« Reply #19 on: January 15, 2010, 09:31:39 AM »

Van, that idea ia brilliant, our generator is a 3000 watt honda, extremely quiet but we also carry a DJ system with 10,000 watts of raw power, if we were to crank that with an 8 hour load of rap or hiphop, I'd be willing to bet nobody would complain about the generator sound lol.
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Van
Billy Van Hagen
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« Reply #20 on: January 15, 2010, 09:39:20 AM »

Just took these



 Grin
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« Reply #21 on: January 15, 2010, 12:49:45 PM »

Oh gosh, I guess I should pay more attention.  I thought you were talking about a big genny. . . ignore me please. . . (it's not hard, people do it all the time, ha ha.).  Christy
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Van
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« Reply #22 on: January 15, 2010, 01:06:21 PM »

Alright Cody Grin! You bring that stuff, and I will most certainly park next to you guys LOL Grin
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« Reply #23 on: January 15, 2010, 03:29:30 PM »

After over 50 yrs of using conduit pipe now I find out it is EMT and I didn't even know it all this time!!
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« Reply #24 on: January 15, 2010, 04:06:16 PM »

And all this time I thought EMT stood for Emergency Medical Technician!  Shocked
Grin  BK  Grin
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« Reply #25 on: January 15, 2010, 08:52:25 PM »

Me too!!
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