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Exhaust Question

k91 kohler generator

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#1 dodge trucker OFFLINE  

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Posted June 08, 2014 - 09:45 AM

I have a Kohler 1750 generator  powered by a K91  4HP that I bought last year as a camping generator.

It had the typical Kohler "pancake" muffler on it when I got it.

It isn't "that" loud (to me anyway)  I know that what is "loud" is subjective. I figure on putting this out under the back pull out of my popup camper while out at the campsite.I have a "2 way" fridge on board that runs off of either 12V (thru the on board power converter) or propane. I also have a 5000 BTU A/C  that would be my main need for 110V. while out camping.

 

I found a much larger muffler for it via Ebay shortly after I bought the generator a brand new but probably 30 year old Nelson Spark arrestor muffler  that is probably ~3" diameter and 10" long, meant to slip over and be clamp to a piece of 3/4" water pipe.  If my K91 were threaded for pipe like some are,  it would be 1/2", judging by exhaust port size.

 

I had somebody make me a flange out of 1/2" plate and I plan on using a piece of scrap 1/2" electrical conduit about 4" long that I bent via conduit bender to about a 45* arc

My plan is to weld the conduit to the flange (that will then bolt to the motor) then weld a short piece of 3/4 water pipe to the conduit as a sleeve  on the other end of this piece of conduit to size up to the muffler inlet.

now the water pipe will hardly be seen as it will all be within the muffler except maybe for ~1/4" or so;

 

What I have in mind is much like some of the old minibike mufflers that had a standoff pipe between the muffler and engine; the old Snapper riders had something like this too. I have some 1/8X1/2 metal strapping that I plan on making a support with,  for the other end of the muffler as a "standoff" from the engine

 

My questions are; will the conduit hold up to the heat OK?  and also, being the pancake muffler bolted up flush to the block and its inlet was the same size as the exhaust port, my idea will have the exhaust dumping into a smaller opening (just by the thickness of the tube, which is about 1/2 the thickness of water pipe) most thinking on exhaust seems to be "bigger tube is better" for breathing... the amount that the conduit is smaller than the port, shouldn't choke off the exhaust  "too" bad, will it?

 

 


Edited by dodge trucker, June 08, 2014 - 04:02 PM.


#2 dodge trucker OFFLINE  

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Posted June 08, 2014 - 11:04 AM

If what I'm seeing is a date code the muff  that I am wanting to use is older than I thought.  11   71   NMC  T-9995 

and it says "SPARK ARRESTOR" right on it.

Its new old stock I got from Ebay last year for $20.  I bought 2 from this guy  this one and a larger one like what is seen on older cast iron Tecumseh and 10-12-14HP K series Kohlers... (have otehr plans for that one) 


Edited by dodge trucker, June 08, 2014 - 04:01 PM.


#3 toppop52 OFFLINE  

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Posted June 08, 2014 - 02:54 PM

I can't speak to the conduit holding up, but I will say the longer the pipe, the cooler the gasses, the slower the flow and the smaller the pipe and muffler needed and even desired, will be, in order to maintain flow velocity for proper engine output.


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#4 dodge trucker OFFLINE  

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Posted June 08, 2014 - 04:07 PM

ok I have my exhaust pipe made up  when all is said and done I used the piece of water pipe to tighten the radius of it to ~75-80* and my MIG welder to seal up the difference in pipe diam. from the conduit to the heavy wall water pipe, the water pipe portion wound up at ~1-1/2" long.  now to take a die grinder and clean up the conduit portion from the inside part of the radius inside the water pipe beyond where it is welded. I think it looks good  but well see once its all bolted up and running what it sounds like..

 

toppop  you want slow velocity? I thought the idea was at last equal flow potential to what ever air that you get in via the intake side if not a little more?


Edited by dodge trucker, June 08, 2014 - 04:10 PM.

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#5 toppop52 OFFLINE  

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Posted June 08, 2014 - 09:46 PM

ok I have my exhaust pipe made up  when all is said and done I used the piece of water pipe to tighten the radius of it to ~75-80* and my MIG welder to seal up the difference in pipe diam. from the conduit to the heavy wall water pipe, the water pipe portion wound up at ~1-1/2" long.  now to take a die grinder and clean up the conduit portion from the inside part of the radius inside the water pipe beyond where it is welded. I think it looks good  but well see once its all bolted up and running what it sounds like..

 

toppop  you want slow velocity? I thought the idea was at last equal flow potential to what ever air that you get in via the intake side if not a little more?

No, you want to maintain velocity in order to scavenge the gasses and avoid reversion at the exhaust valve. In order to do that, especially on gas engines, you generally get smaller nearer the end of a long system, virtually all performance cars in the 60's with dual exhausts came from the factory with either 2.5" front pipes and 2.25" tail pipes or 2.25" exhaust pipes and 2" tail pipes. Only very high compression, high rpm engines or super/turbo charged engines need large diameter pipe to the end. The smaller pipe further away from the valve will tend to quite the noise as well.


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