Intake silencers gone missing?

[amuller]

Wondering if the experts here could shed some light on why various motors ceased to have intake silencers. Just a couple of examples:

The 5.5 "Fisherman" motor long had what looks like properly designed silencers. But my ’62 only has the fiberglass pad in front of the carb.

My ’57 12 hp Elgin (West Bend made) has an intake silencer box. My ’61 West Bend, basically the same motor, does not. Just the bare carb.

I have some speculations of my own but wondering what others know about this.

am

[wedgie]

Cost saving measure no doubt.

The fiberglass cowl showed up around the time the silencers disappeared. The fiberglass was pretty good as a soundproofer compared to the all metal covers.

[dan-in-tn]

Im with Wedgie, but the silencers keep coming back. I suspect it has to do with the noise the particular engine model puts out. Along with that the design of the motor cover as far as if it is open in the front. Rope starts have some openings in the front. Also the silencers kept getting cheaper to make. CPS (Cheap Plastic S**t) in later years allowed them to come back without much cost. Marketing is sensitive to other manufacturers hype. Quite engines sell. 4 strokes are quite so make 2 strokes quiet. Just my opinion, I may be wrong!

Dan in TN

[vintin]

Just an observation but I wonder with the flywheel so close to the air silencer why no ‘ram air’ systems were developed. Maybe there were as it seems a natural. Pun intended.

[chinewalker]

It was discovered on some models that there was a slight tuning effect with the silencer in place. There is a small standing wave in front of a carburetor while it is running. If that wave can be "bounced" into the carb throat at the right time, it can have a small charging effect, in addition to noise deadening. A friend of mine who was heavy into outboard racing tested this with an Evinrude 15A, using a plate in front of the carb while running on a test wheel. The tach showed about a 50-100 RPM difference depending on placement of the plate. Best placement was about where the carb cover would normally sit in front of the carb.

[amuller]

quote Chinewalker:

It was discovered on some models that there was a slight tuning effect with the silencer in place. There is a small standing wave in front of a carburetor while it is running. If that wave can be “bounced” into the carb throat at the right time, it can have a small charging effect, in addition to noise deadening. A friend of mine who was heavy into outboard racing tested this with an Evinrude 15A, using a plate in front of the carb while running on a test wheel. The tach showed about a 50-100 RPM difference depending on placement of the plate. Best placement was about where the carb cover would normally sit in front of the carb.

Yes, I think a properly designed inlet tract should be able to give a power increase as well as quieter operation.

But the OMC plate with fiberglass on it? Is this intended as a reflector, or a partial silencer, or what ???

Is there not also the possibility of that "standing wave" containing fuel, or fuel vapor? I’ve wondered if a possible hazard exists with the carb inlet pretty close to sparking points.

[frankr]

The ring and groove around flywheels and armature plates are a firestop. Now about those leaky spark plug wires…maybe they should e replaced?

[mr-asa]

quote amuller:

Is there not also the possibility of that “standing wave” containing fuel, or fuel vapor? I’ve wondered if a possible hazard exists with the carb inlet pretty close to sparking points.

I don’t think so. You might get a very very small amount, but the majority would drop out of suspension

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