Is there any way to make two-strokes just as quiet as four-strokes?

[fuzzybabybunny]

I'm really interested in two-stroke motors for a number of lightweight / compact applications, such as paramotoring (carrying the motor on your back) and in lightweight and compact motorcycles. I really don't like the loudness nor the sound signature of them though.

Are there any effective ways of making them just as quiet as four-stroke motors? I've heard of a snorkel that people have put over there exhausts but the company that makes them is no longer in business, not to mention the snorkel doesn't seem to have actually done much to decrease the volume.

Why are they louder anyway?

The only other lightweight motor that I know of that can match the quietness of a four-stroke is an electric one, but then you have a number of other downsides such as lower range / operating time and having to charge a battery for hours after it's empty.

 

[RLGL]

Due to the way fuel is delivered thru the crankcase to the top of the piston a muffler will restrict the delivery of the fuel ( back pressure ) . This is one of the reasons the marine industry is dropping 2 stroke engines, a catalytic converter will not tolerate the amount of wasted fuel that goes out the exhaust. The standards for converters are in the process of being set by CA.

 

[monkeydelmagico]

no

 

[fuzzybabybunny]

Due to the way fuel is delivered thru the crankcase to the top of the piston a muffler will restrict the delivery of the fuel ( back pressure ) . This is one of the reasons the marine industry is dropping 2 stroke engines, a catalytic converter will not tolerate the amount of wasted fuel that goes out the exhaust. The standards for converters are in the process of being set by CA.

Hmmm... Interesting. So because...

- the exhaust out of the piston chamber

- the movement of the air/fuel mixture from the crankcase into the piston chamber

...happen at overlapping times, having anything over the exhaust would restrict the exhaust as well as the delivery of the air/fuel mixture, right? Wouldn't this simply lead to reduction of power output or would it just completely screw up the entire cycle? Would such a restriction limit power that much? A two-stroke of a certain cc already makes twice the power of a similar cc four-stroke.

 

[rstrohkirch]

I'm not familiar with engines that small. I'm familiar with bikes in general and I will say it's entirely up to how you design the engine. Small 2 stroke engines are generally used in the manner they are because of the power they generate and the maintenance they require in their package size. What's the point of making this smaller lighter engine and then restricting it's output to that of a 4 stroke. However, if you look at something like a trials 2 stroke you'll find they sound almost like a 4 stroke and have power characteristics more in line with them as well.

Also, the idea that a two stroke makes 2x the power per cc is not true. 4 stroke engines have come a long way in serious power sports environment. They still generally weight more though for a given engine size but their hp/tq numbers are 70-90%.

I would assume though that engines you're referring to are going for maximum output in their size/maintenance schedule so they won't be quiet. High performance 4 strokes usually aren't quiet either to be honest. They are far far worse for noise pollution as their lower frequency exhaust notes travel drastically further.