: Why lawnmower mufflers suck

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Car/Truck mufflers do amazing work muffling noise. A car is nearly silent when running with a muffler, compared to what it would sound like with open manifolds. When I fire up my Honda push mower, the whole neighborhood knows about it, and it’s actually kinda quiet as mowers go. So eli5 : Why can’t lawnmower mufflers work like automotive mufflers?

In: 29

Well a car muffler is about 100x larger. That’s why. The sound bounces around way longer before exiting the muffler. If you attached a larger muffler on a mower it would be quieter, but it would also be more expensive and much heavier to push around.

Too much backpressure on the small motor that cannot make enough pressure to operate a large restrictive muffler

Mainly they don’t work as well because they don’t have to. Regulations on auto noise is much more limiting than on lawn equipment. If lawn equipment manufacturers were required to meet a lower decibel level, they would invest in the engineering and materials to meet those requirements.

It is probably due to consumers not willing to take on the cost value for development. Will most people pay $100+ dollars more than any other model available just because it claims to be a little quieter and looks odd and heavy compared to what you expect a mower to look like?

While many here claim it is a physical constraint, Honda’s small power generators are much quieter than any combustion lawn mower. The existance of electric lawn mowers is probably also a contributing factor.

It’s a lot cheaper to buy an electric lawnmower than to put a car-grade muffler on a lawn mower. Nobody would spend 2-3X as much on a “quite mower”. Car noise is easier to control, because cars are huge and you can have space for all sorts of dampening devices, water cooling, exterior panels with sound insulation, … that would’t make any sense in a mower.

Money.

You could probably fabricate a decent fiberglass packed muffler if you had a welder, spare sheetmetal, and time. If something like this actually came to market it would probably make a killing.

Possibly for the same reason vaccuum cleaners are so loud, people won’t buy a quiet one because the perception is they have no power?

There is a push in some cities to ban or severely restrict a lot of these small gas powered devices (lawnmowers, leafblowers etc.) due to both physical and noise pollution that they create and the health damage they cause to the operator.

Hour per hour, your long mower produces 11x as much pollution as a car built in 2022. Considering that a lawn can be maintained with a push, electric, or battery power mower, and only an extremely overgrown lawn needs the torque provided by a gas engine, regulation makes a ton of sense.

Most of the noise isn’t from the exhaust, it’s directly through the block or cylinder head on a small air cooled engine. You can see some experiments on YouTube.

I travel for business, and whilst I was gone my Mrs couldn’t get the mower started (neither could the neighbor) I told her to go buy a spark plug. She went and bought an electric mower.

I hated that thing, it definitely makes you stay on your toes. Unless you have a half dozen batteries laying around you don’t want that grass to get too tall.

But other than that…. Man I love that thing. So quiet I can mow at 6am! And it’s half the weight of gas.

Because a good muffler is the same size and cost as a lawn mower. Nobody is going to pay 2x the cost for a quiet mower, especially when battery mowers are taking over anyways.

Your car has 10 feet or more of exhaust pipe, a catalytic converter, a muffler, and likely a resonator all in its exhaust system. A lawn mower has a tiny muffler bolted to the cylinder head.

You need to have time (pipe length) for the exhaust gas to cool down, and chambers to allow the gas to expand and contract (resonator, muffler), and ideally, internal baffling or packing in those chambers to slow the exhaust gas further, giving it more time to cool to achieve a quiet system.

You can build a quiet exhaust system for your mower, but you’re going to lose a lot of power, and you’ll have a pipe array that is 5 or more feet long.