Drilling into muffler cup

Discussion in 'Intake & Exhaust' started by geoldr, Jul 6, 2011.

  1. geoldr

    geoldr New Member

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    On my youtube one member of this forum commented saying that if I drill holes in the muffler cup it will increase power in in the straights. Is this true? And how do I do that? Just drill straight into the muffler from the opening?
     
  2. 2door

    2door Moderator

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    Your power increase will be minimul but the noise will increase a lot. Some believe that if it's louder then it must be faster. That's a myth. The slight increase you might experience is not worth the aggravation you'll cause your neighbors or the negative effect it will have on the hobby.
    There are aftermarket exhaust systems, expansion chambers, that will positively effect your power output but drilling holes in your muffler is not the way to go.
    Tom
     
  3. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    Tom knows. Heed Tom. Expansion chambers are a way to adjust your back pressure in a more precise way. And a two-stroke needs a certain amount of back pressure to hold an air-fuel charge and to function properly.
    Drilling holes in a muffler is not a very precise way to adjust back pressure. Hole too big, too many holes = problems. You'll have inefficient combustion, you may even end up with a LOSS of power if you overdo it, and you might find yourself shortening the lifespan of the engine over the long run.
    And, as Tom mentioned, making a Gawdawful racket will bring unwelcome negative attention to our hobby.
    I know money's tight (four daughters, believe me - I KNOW) but saving back and getting the right equipment is truly the way to go.
    Ride safe.
     
  4. GearNut

    GearNut New Member

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    Please don't drill holes on your muffler.
    As was stated before, 2-stroke engines need a properly tuned expansion pipe exhaust system for excellent power increase. If done properly with a good muffler it can nearly double the power output and be just as quiet or even quieter that the factory muffler.

    I have been in the Harley-Davidson industry for nearly 20 years now.
    The old adage "Loud Pipes Save Lives" and the notion of "louder means more power and faster" has been a thorn in the side of the industry for longer than I have been alive.
    What has that really done for the industry?
    Mandatory factory exhaust as installed and equipped when the bike was first sold for all motorcycles manufactured after 1982.
    Random decibel testing at "safety" inspections sprinkled around popular ride routs.
    In some states and cities/ counties, if a peace officer cannot find the correct factory stamping on the muffler's canister your bike can be impounded on the spot. Even if you are from another state and passing through to say Sturgis or Laconia bike rallies.

    A few bad apples have ruined things for all who enjoy modding their bikes responsibly.
    That said, the AMA and MMA and Abate have been successful in postponing some of these draconian laws into coming to effect so far.... but the noose has been tied.

    We in the Motorized Bicycle world have no AMA, MMA or Abate to lobby the lawmakers and judges. If the law decides that all MB's everywhere are too loud to be legal, we all are screwed. Never mind that many are just as quiet as a weed eater, lawn mower or even quieter.
     
  5. BarelyAWake

    BarelyAWake New Member

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  6. Mike B

    Mike B New Member

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    Yes, I think it is even a federal offense to modify a factory stock exhaust system.

    But I get Harleys with straight pipes loud enough to rattle the windows go by my house every day.

    I hate them. I am going to start writing letters demanding the existing laws be enforced.

    I would like their bikes to be impounded, they be made to reinstall a factory exhaust system and pay a nice fat fine or do a little jail time or some community service.

    No regards for anyone but themselves have they.
     
  7. biknut

    biknut Active Member

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    It all depends on which exhaust pipe you're dealing with. In any case drilling the end cap probably isn't the hot set up.

    I would suggest taking the muffler apart and inspecting the baffles. The most recent kit I bought had a very restricted muffler that needed to be modified just to run well. After opening up the restriction a little it runs very well and is close the quitest I've heard.

    Here's a before and after

    [​IMG]

    [​IMG]
     
  8. dmb

    dmb New Member

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    i love the sound of the old 2,3 and 4 cylinder two strokes at the races.speedway yes xr750's yep, iv'e stood with the starter with 2 top fuel funny cars at ocir [your brain shakes] but those kids on the 50cc 2 strokes raceing around the camp site at 6am would drive me nut's
     
  9. peeduh

    peeduh New Member

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    Do what YOU want. It's your bike.
    out of the people that I've met by running into on the streets on gas bikes, only one had his cap still on, both older and younger than me so it's def not an age thing.
     
  10. IreBo

    IreBo New Member

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    well i have to say that i have 6 gas bikes and every one of them i have messed with the exhaust but one and it is the slowest bike in the fleet and is the same model and engine as 2 of my others. i first drilled 1/4 hole in the cup. it made a slight diff. then i started to make bigger holes and even cut the pipe in side the muffler. ive used grinders to slot the bottom instead of holes, and even just took off the cap and drilled into the tube to get more flow while trying to keep noise down. all mods did help power at topend and took a bit away from bottom end, ie takeoffs. the motor runs way better being unrestricted. idle and overall vibration was improved. i modded a rudimentary expansion chamber (banana style) and that got my top end more rpm's fore sure!!

    but i think that no matter what you do you will never be as loud as a Harley with a set of screaming eagle pipes on it.they are a factory upgrade from the dealer. those are seriously loud and rattle everything when they go down the rode... almost painful to be next to one. i think some folks chiming in live in towns in jurisdictions that are much stricter than others. shoot i live in California. one of the most restrictive, overly progressive, anal places in the U.S. and have been followed by a cop that thought i was on a scooter (go ped) when he saw it was a bike he said sorry and to continue on my way....said if it was a scooter he would have confiscated it. and he also said "nice bike, ive been thinking of building one myself..." so even cops are into them!

    i say give it a shot! ride up a hill, pay attention to the power , then take off the cap with the one screw and try the hill again.... you will notice more power and the motor doesn't make that pre detonation tick. if you don'tlike the power just screw the cap on.... i keep a leatherman in my pocket and remove the cap as needed.. i go on some long back country rides and notice a fuel savings and more power. i cork it back up when i get into town...EZ!

    dnut

    i can also understand the folks who want to keep motorbiking on the low down as we are really in a gray area and in these times all governments are looking for more ways to generate revenue , but that's ware the system comes in. a petition and a strong seance of unity will make these super fuel efficient rigs legal some day if we really wanted!! power to the people!!
     
    #10 IreBo, Aug 19, 2011
    Last edited: Aug 19, 2011
  11. Ernst

    Ernst New Member

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    Expansion by SBP and Stinger is a hot water flexi pipe and the muffler is a tractor supply 3/4 inch off the shelf.

    I have great power for the weight the bike carries.

    The engine noise and the exhaust noise are separated for me.

    When the bike is running at 28mph which is my highway speed there is a satisfying balance of running noise.
    At 2 am or so it will not make any friends but the sound is relative to the small engine it is.

    I wouldn't drill holes in the muffler myself. I went with a better exhaust,
    Again separating the engine sounds from the exhaust sound made a difference in my enjoyment of riding my MaB

    [​IMG]
     
  12. geoldr

    geoldr New Member

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    Ah ok. This post was a while ago, and I have had a SBP x chamber for a while now. Really like it!
     
  13. Mozenrath

    Mozenrath New Member

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    I'm not much of an MB expert, to be honest, but I'll contribute my opinion.

    When I ran my engine for the first time, I my muffler didn't fit on yet, but I was eager to ride so I went without it. In comparison to having the muffler on it, it was DEFINATELY faster to some degree across the whole power band. I know one could say that it's a placebo due to the increased sound, but there seriously was a major difference.

    That being said, somehow I doubt that a small hole would make much of a difference, both as far as power and sound go. You would have to remove a lot more of the back pressure to make a difference to justify the increase in noise. I remember somebody made a modification where the end cap could be actuated with a lever; that way if the rider was going up a steep hill, the end cap could be pushed away from the muffler and cause the engine to run leaner and have a little extra speed. Unfortunately I don't remember where I saw it, but that sounds like a better mod for speed because you could still run the engine at the proper richness and dynamically lean it out when it's necessary. Not sure how safe that is, though.

    My replacement end cap that I made has no baffle tube, and it only sounds a tad bit louder IMO. In fact, a few people have asked me if I made my bike quieter, so nobody has noticed the difference. I have noticed though that the engine runs a little better. Not by much, but it seems to be breathing a little better. The baffle tube hardly does anything, so if you want to do everything possible to maximize performance, cutting off that baffle tube can't possibly hurt.
     
  14. locutus_1

    locutus_1 New Member

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    all of you guys have to learn these little bitty engines arent made for performance.. its not worth the .3 hp your going to get.. 2 or 3 hp then you notice.. but all these little things do nothing.. its just to take your money to spend on carbs and etc.. you want power you get a morini motor or dirt bike 125 motor and install it in your bike.
     
  15. geoldr

    geoldr New Member

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    The fun of it is in the tinkering around. Your suggestion of buying a dirt bike motor and putting it on your bicycle is probably the worst suggestion you can give. Our bicycles were never meant to go that fast. If you will be spending the money to get a morini or anything else that is that expensive, you might as well just save up a bit more and get a motorcycle. A used Kawi Ninja 250 goes for very little. And its a lot better than a bicycle.

    And you should read the thread first. It well agreed upon that drilling into muffler cup is not worth it.

    Thanks.
     
  16. electron

    electron New Member

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    Might keep this 1 going...
    After reading about drillin holes, etc i decided i would change the flow, but not the backpressure, so i cut off the removable tube section and drilled through the remaining inside section keeping the external piece and weld, of course. This made a smooth exit. On the 80cc(66) it sounded a fair bit louder and more agressive/ dirt "bikier" and with the carby ground out another 2mm diameter resulted in heaps more torque and response, but not change in top speed on the flat. This mod helps up hills and attract jusr enough attention so people know i'm commin'.
     
    #16 electron, Sep 14, 2014
    Last edited: Sep 14, 2014
  17. G3R0N1M0

    G3R0N1M0 New Member

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    I removed my cap and the difference greatly noticeable. It could easily do a burnout (in dirt). The climbing power was increased,plus more throttle response. The only down side was how loud it was. Now its crazy loud. But at least people know I'm coming.

    .duh. dnut
     
  18. 2door

    2door Moderator

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    You're not doing the hobby any favors. Negative attention we don't need. Your power increase is negligible and mostly in your head. If it's louder, it must be faster. Not true. There are exhaust modifications that will increase performance. Removing the cap from the muffler isn't one of them. Put the cap back on.

    Tom
     
  19. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    I have to agree with Tom here. The only thing I could add is that you may want to also check what a lack of calculated back pressure will do to the way the two-stroke engine uses fuel. An expansion chamber is generally a better choice. And I think you may end up finding out whether there is a maximum permissible decibel level in your area; some cop may come and talk to you about that. There are headaches that can come with making the decision to de-cap-itate your muffler. The previous posts in this thread cover more detail.
     
  20. G3R0N1M0

    G3R0N1M0 New Member

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    I will put the cap on it. It seems to drink a lot more gas with no cap. Probably the lack of back pressure. But i have to buy a new one the old one got bent and broke. So time for that great 3-5 day waiting period we all love so
    .duh.dnut
     

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