Better muffler for small engine?

  • Thread starter Thread starter Sherwood Botsford
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Discussion Overview

The discussion revolves around finding a better muffler solution for a 9 hp Subaru engine used in a soil mixer, focusing on reducing noise levels. Participants explore various structural designs and configurations for mufflers, considering factors such as engine type and exhaust direction.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that many small engine mufflers function primarily as spark arresters and suggests that a bell-shaped structure could help direct sound energy upward.
  • Another participant inquires about the engine's specifications, asking about the number of cylinders, stroke type, and RPM stability.
  • A participant clarifies that the engine is a single-cylinder, four-stroke running at a constant RPM, likening it to a large lawnmower engine.
  • Suggestions for muffler designs include using a chimney stack silencer with a larger pipe and positioning the outlet above the user's working level, or directing the exhaust horizontally away from the user.
  • Another idea involves feeding the engine exhaust into a large oil drum fitted with baffles to reduce noise while ensuring adequate flow area and drainage for condensation.
  • A participant shares an anecdote about a sawmill engine that effectively used a rusty truck silencer, resulting in minimal exhaust noise.

Areas of Agreement / Disagreement

Participants present multiple competing views and suggestions for muffler designs, with no consensus reached on a single effective solution.

Contextual Notes

Participants have not fully explored the implications of different muffler designs on performance or noise reduction, and there may be assumptions regarding the effectiveness of proposed solutions that remain untested.

Who May Find This Useful

Individuals interested in small engine modifications, noise reduction techniques, or those working with similar machinery may find this discussion relevant.

Sherwood Botsford
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I have a 9 hp subaru engine that operates a soil mixer. I find it obnoxiously loud. From other reading the 'mufflers' on many small engines are little more than spark arresters. The location of the engine (about 6 feet off the ground, and the exhaust (on top) make me think that it should be possible to direct most of the sound energy upward with an appropriate bell.

Suggestions as to the actual structure appreciated. Do I want massive? light weight? exponential curve vs stepped?
 
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How many cylinders ?
2 or 4 stroke ?
Does it run at a fixed RPM ?
 
1 cylinder (who makes a multi-cylinder 9 hp utility engine?)
4 stroke.
Constant RPM

Think big lawnmower engine.
 
Chimney stack silencer - use pipe a bit bigger than one fitted to engine and arrange outlet well above your working level .

Similar but go horizontally and have the outlet some distance away from you and ideally behind a hedge or a wall .

Feed engine exhaust into a large oil drum or similar fitted with alternate baffles .

Always allow for very generous free flow area in exhaust system extensions . Make provision for condensation to drain away when engine is not in use .
 
I once came across a saw mill engine where the normal engine exhaust was being fed into a large and very rusty truck silencer with the exit end poking out through the equally rusty shed roof .

This set up worked well and there was very little exhaust noise to be heard .
 
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