Honda GX35 Noise Reduction?

[bigoilbob]

I am using the power from my GX35 build fairly efficiently with a Nuvinci Developers kit. I am able to power my Bike E2 tandem recumbent from ~4-18 mph up and down hills with 2 aboard. But my power to weight ratio is obviously low. I make it up with low gears and a wide (~3.5) transmission range.

But I would like to be quieter. The GX35 is not a total buzzer, but I keep it in the 5000-7000 r/m band and it is certainly audible, especially to the passenger. That is often me, as I let my wife drive. What can I do to reduce it's noise, in a way that I won't hurt the engine or overheat it. I am ok with minor power reduction.

I did the good doobie thing and searched first, unsuccessfully.

Thanks all;

Bob

 

[darwin]

Check some of the vendors here they have those long pipes that should do the trick, some are flexible.

 

[Deleted Member 4613]

I made a silencer for my Tanaka 2 stroke and will soon test it. May make a video if it
works.

 

[HeadSmess]

how good are you with silver solder, a blowtorch, and various empty aerosol cans?

basic theory is to have as large an expansion volume as possible to "weaken" the pulses, then have two tracts of different lengths that cause "destructive interference" when the pulses come out the other end slightly out of phase.

lots of baffles, lots of volume.

and as previously stated in so many threads...at some point INDUCTION noise becomes the major player.

then theres the fact that air cooled engines are always a bit noisy...

 

[bigoilbob]

Thanks Headsmess, but don't have those skills

One of many skills I don't have. Frankly, I was hoping to glob on to someone else's knowledge for a largely prefab solution. So many of these engines out there, and I know many are used for motorized vehicles and/or RC. So, I thought someone would have easy ideas. A kit would be ideal, but I would be happy with a build thread.

I see some ideas for more power/noise, but I want LESS noise and am willing to give back a little power.

But do appreciate it!

Bob D.

 

[loquin]

Add a longer tube, (3-5 feet long, most likely 'folded') after a 'swiss muffler' about 18 inches long near the existing muffler outlet. Frankly, the longer the exhaust tube, the quieter it's going to be, and the lower the pitch. Four-strokes are much more forgiving than two strokes, when modifying the exhaust, so long as the exhaust isn't overly restricted.

ref this post on swiss muffler.

 

[mechcd]

I have been wanting to try something like this on my EH035. It hooks in line with your existing muffler. I'm a bit worried about how much restriction it would add along with mounting it. I think most 4 strokes would need a 90 degree bend so that the extra silencer isn't sticking way out the side of the engine.

http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4389/.f

I have tried using about a foot of silicone RC exhaust tubing hose clamped to my stock muffler, and it really helped either quiet it down or at least redirect the noise away from me and bystanders, but bogged down the engine to the point where my cruising (high?) speed went from 25 mph to around 21. Using larger diameter tubing would probably help with this but would make attachment to the stock muffler more difficult. Also, I had the tubing gently snaked down the GEBE mount and secured with zip ties. When the engine and tubing warmed up, it would get soft and kink, causing the engine to die or the hose clamp and tubing to blow off. A brass or copper 90 degree elbow from the hardware store would probably fix that problem but I never got around to trying it and managed to misplace the tubing.

 

[Happy Valley]

A degree of care and consideration is needed with restricting the exhaust flow on these small 4 strokes by simply adding further muffling after the stock muffler. I've tried a number of schemes and then disassembling after noted excessive carbon build up at the exhaust port, exhaust valve and piston crown. If I want to experiment more with silencing I think it necessary to eliminate the stock muffler and design it with a header from the cylinder exhaust port.

 

[bigoilbob]

Many thanks, Happy Valley. I think I will take your advice. Timely, because I am ready to get started.

Appreciate it!

 

[Happy Valley]

It sounds like you already have a plan so good luck with that. Over the past several years I've tried a number of different solutions and made a cursory study of exhaust design. I've found it to be one of those things that the more you learn the more you realize it's a pretty exacting science.

One good thing is small engines like the GX35 or EHO35 are pretty quiet to begin with, relative to the 2 stroke weedwacker engines of equal size. It's possible to muffle them down to the point of effecting performance and even further to possible damage to the engine. After quieting the exhaust note, one realizes it's half the picture, intake noise then becomes more apparent.

I've found a good model to perhaps ponder is scooter design. I ride with a friend who has a Yamaha Zuma 50cc scooter. Though it's a 2 stroke and larger than the EHO35 for example, it is actually quieter because the engine in enclosed in the seat cowling, and utilizes an airbox on the intake. The exhaust is comprised of a long header off the exhaust port and runs to a fairly heavy gauge steel muffler/tuned chamber that must weigh at least 10 lbs. Of course, as a scooter, it's pretty heavy to begin with, about 160 lbs, but I think it worth considering adapting some of the design logic utilized in making them fairly innocuous ICE powered vehicles.