Honda GX35 Noise Reduction?

Discussion in '4-Stroke Engines' started by bigoilbob, Feb 20, 2012.

  1. bigoilbob

    bigoilbob Member

    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;


  2. darwin

    darwin Well-Known Member

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

    Mike St Member

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

    HeadSmess Well-Known Member

    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 some point INDUCTION noise becomes the major player.

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

    bigoilbob Member

    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.
  6. loquin

    loquin Active Member

    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.
    Last edited: Mar 16, 2012
  7. mechcd

    mechcd Member

    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.

    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.
  8. Happy Valley

    Happy Valley Active Member

    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.
  9. bigoilbob

    bigoilbob Member

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

    Appreciate it!
  10. Happy Valley

    Happy Valley Active Member

    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.
  11. WheeledWonder

    WheeledWonder New Member

    Silicone exhaust tubing

    Has anyone tried something simple, like slapping the 6-inch silicone tubing that Sick Bike Parts sells onto the end of the stock muffler?
    How much did it quiet things down from the rider's perspective? From the audience's perspective?
  12. Happy Valley

    Happy Valley Active Member

    Adding a piece of tubing to the stock muffler of these small utility engines offers negligible noise reduction from dB sound meter readings. But give it a try if you'd like and BTW you don't need silicone, common black, automotive heater hose in the appropriate size found at most hardware or auto parts holds up well enough for a trial.
  13. WheeledWonder

    WheeledWonder New Member

    Well, okay...

    Thanks Happy.

    So...what about ganging 2 or 3 stock mufflers onto the existing stock muffler?

  14. WheeledWonder

    WheeledWonder New Member

    Other possibilities

    So for a rear-mount friction drive setup:

    Has anyone tried a mid-engine 50cc muffler like the Standard One Piece that sells?

    Did you simply leave it as-is, so the muffler pointed to the front?
    Did you bend it around, so the muffler pointed to the rear? If so, how did you effect the bend (weld in a U-turn, use flex-piping, etc.)?

    Has anyone gone all-out with their #6 Poo Poo?
  15. Happy Valley

    Happy Valley Active Member

    Yes and no, I've tried similar pipes but not the one from that company.
    One issue to begin with is matching the bolt hole centers for the exhaust flange and port size. You would need to measure yourself to ensure proper fit but IIRC these size engines have a 32mm bhc and 10mm round exhaust port. Those sizes are much smaller than most of the ready made products so making or having made your own exhaust header flange becomes necessary.
  16. rawly old

    rawly old Member

    Gee, they don't come much quieter that a stock gx35
    to begin with. I can barely hear mine from 50 feet away.
    It's far quieter than the average lawn mower. This is
    such a dependable little engine just the way Honda has
    engineered it; I really don't want to mess with it.
  17. bigoilbob

    bigoilbob Member

    Point quite well taken, rawly old. I sure agree with that dependability part. I wince when I read about the troubles folks are having with their sino powered MB's. I get one little hesitation, one time, when I start out too cold. Otherwise, hot weather, heavy duty climbing, long idle at stop lights, no problem. It runs like a train. And it is quiet compared to many other builds, especially those with no forced air cooling.

    I would not do anything that the motor could "see". No tuning, no extra back pressure. But my build is a recumbent tandem, with the motor/gearbox/charging system right behind the rear seat. My wife say it's loud. All moot for now. I'm in the Kingdom of Saud during the week and Dubai on weekends until mid October. But when I get home (for good this time, I always say), I think I will investigate further.
  18. bigoilbob

    bigoilbob Member

    Need to call BS on myself, B4 someone else does. When I use a word I should know what it means. MY bike is "sino" powered. I'm referring to the engines I read about, that seem to mostly come from China, that cause so many folks to write in complaining.
  19. Richard H.

    Richard H. Member

    IMO quiet is good, certainly worth pursing doing what you can to quiet the exhaust noise, the issue isn't at idle but at revs. I have a GX35 and while it's a great little engine it often gets left behind in favor of an electric bike I have. The quiet of the ebike has become addictive.
    Last edited: Sep 22, 2012
  20. rawly old

    rawly old Member

    If I addressed all my wife's complaints, I would
    have little time for anything else.:devilish:

    ear plugs?
    Last edited: Sep 22, 2012