Homemade exhaust extension - Montana Owners Club

edmojenks · 09-03-2010, 05:13 AM

I have what I hope is a simple question. I am making an exhaust extension for my twin Honda 2000i generations. Extensions are required for tailgating at LSU. I have a 1 inch exhaust on the generator and have constructed a 5" X 5" L joint that goes from the generator to where I would put my 10' extension pipe to run the exhaust to the top of my fifth wheel. Of course I am wanting to take every precaution to stop any back pressure. I know the manufactured exhaust extensions allow for air escape at the bottom of the extention pole and that serves to prevent back pressure.

Here's my question? Since I have a 1" pipe coming directly from the exhaust, would a 2" extension pipe be adequate enough to prevent back pressure. I know that the standard models have a 3" pipe, but the 2" pipe is so much lighter and easier to attach to my fifth wheel ladder.
Of course I would rather be 100% sure of my safety than complaining about having to handle a few extra pounds. But, if a 2" pipe is perfectly okay, I'll go with that.

Thank you in advance.

bncinwv · 09-03-2010, 05:45 AM

It sounds simple, but it is actually a complicated engineering question. With any kind of pipe flow (gas or liquid), there are friction factors (losses from the pipe material itself) as well as what is called head losses (resulting from pushing the exhaust (gases) or fluids from that matter upward. I would tend to believe that the manufacturers are using a 3" pipe because of the results obtained from engineering analysis. Your choice, but from an engineering aspect (represented as my opinion only not a professional opinion), I would go with what the manufacturer recommends.
Bingo

edmojenks · 09-03-2010, 06:17 AM

Just to clarify, I don't have the exhaust pipe attached to the ten foot pipe becauase that would allow for no air flow out the bottom. Acutally, I have the 10" pipe strapped to the side of my ladder. Then, I move the generator, with the L-shaped 1" exhaustion extension tube and place the 1" L-tube just inside the bottom of the 2" X 10' pole. The L-tube only sticks a couple of inches into the 10' pole, but I could make that a few more inches or less if necessary. So, I very much appreciate the need to allow for air flow out the bottom and top of the pole. Obviously a 3" pole would allow for more air flow than a 2" pole. My bascis question is would a 2" pole work 100% as well as a 3" pole? Maybe the answer is as simple as "obvioulsy you would allow for more air flow out of a 3" pole" and I realize that. But if a 2" provides 100% safety as well I would just go with that.

bncinwv · 09-03-2010, 06:34 AM

I better understand now, but it still does not change the underlying premise that the manufacturer most likely (I would hope) had to do some R&D to arrive at the 3" size. I would think that the only way to know for sure is to try it and see if it works. I would be interested in knowing how it works out if you do try it, for no other reason than having the knowledge filed away for future use that may come in handy!! If you have the 2" laying around, sounds like a pretty cheap experiment!
Bingo

Trailer Trash 2 · 09-03-2010, 07:08 AM

Why dont you place a rug wrapped piece of plywood and place that on the top of your monty then let your gen sets work on the roof and no exost system will be needed, pull them up with a rope, place them on the roof mat and hook up the power, too bad they dont make a auto start for them that would be the only problem starting and fueling. why cant you leave them in the back of the TV and run them in there? seems like a afull lot of work for a campout.

SlickWillie · 09-03-2010, 07:47 AM

I'm thinking the large pipe is more for helping keep the pipe cool than anything. The exhaust will draw fresh air around where it is inserted into the larger pipe, thus cooling exhaust gases. (Very similar to the way the newer diesel exhaust tips function.) I'm not an engineer, but I can't see a problem with the 2" pipe. I do think how far it is inserted into the larger pipe will be important tho. May have to play with that to get it right.

edmojenks · 09-03-2010, 09:37 AM

Trailer Trash. YOu do have some interesting ideas. Never even thought about running them on top of the 5er. My only concern that would be the possiblity of them vibrating and eventually work themselves to the edge (and finally fall off).

Actually, my first preference would be to keep them in my TV. However, to do that I would have to buy a 50 amp extension cord and those don't come cheat.

Thanks for the feedback so far. Everything the responders have said so far makes sense to me.

edmojenks · 09-03-2010, 10:36 AM

BNCIN - you make some very good points. It does seem like when all the research and development was geing done they settled on a 3" pipe for a reason.

Here is the logic behind my thinking. I looked everywhere I knew to look on the internet for a exhaust extension for a generator and could not find one. The one's that I found were designed for motorhomes that you hook up directly to the vehichles exhaust pipe. Therefore, that 3" pipe is carrying the load of the single generator that a motor home runs on.

I my case I will be using two 16 amp generator and each will have their own exhaust extension such as I described. In theory, I was hoping that a with a smaller generator you could do this safety with a two inch pipe. Most of all, I want to be safe.

Trailer Trash 2 · 09-03-2010, 11:34 AM

Eddie your right on the vibration, it could pose to be a problem up there. the campground has some very strict rules for a dry camp.

snfexpress · 09-03-2010, 04:02 PM

The Genturi pipe, as others have stated, is for a larger, less efficient (IMHO) generator. When thinking about our specific needs and the generator carrier that we built, we thought about re-routing the exhaust from the Hondas. Most of the info on the Inet comes from boaters who have modified he exhaust, such as by by tig welding an elbow to the existing exhaust and then connecting it to a silicone tubing that is run to UNDER the water line, thereby increasing the back pressure, but significantly decreasing the noise.

We made a carrier for our two Hondas, but I have to say that if you can run them from your TV, then make or buy an extension cord. It only has to be 30 amp (NOT 50) to an adapter for your existing 50 amp cord. Total cost would probably be less than fifty bucks for a 25' cord.

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