Better muffler for small engine?

  • Thread starter Thread starter Sherwood Botsford
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SUMMARY

The discussion focuses on reducing noise from a 9 hp Subaru engine used in a soil mixer. Participants highlight that standard mufflers on small engines primarily function as spark arresters and suggest various design modifications to effectively direct sound upward. Recommendations include using a chimney stack silencer, positioning the exhaust outlet away from the operator, and utilizing a large oil drum with baffles to minimize noise. Key considerations include ensuring adequate free flow area in exhaust extensions and allowing for condensation drainage.

PREREQUISITES
  • Understanding of small engine mechanics, specifically 4-stroke engines.
  • Familiarity with exhaust system design principles.
  • Knowledge of sound attenuation techniques.
  • Experience with materials suitable for muffler construction.
NEXT STEPS
  • Research "Chimney stack silencer design" for effective noise reduction.
  • Explore "Exhaust baffle design" to enhance sound dampening.
  • Learn about "Free flow exhaust systems" to optimize engine performance.
  • Investigate "Condensation management in exhaust systems" to prevent rust and damage.
USEFUL FOR

This discussion is beneficial for small engine mechanics, DIY enthusiasts, and anyone involved in noise reduction for outdoor equipment, particularly those working with soil mixers or similar machinery.

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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