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Why can't I just take off my muffler?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Fa1c0n, Sep 5, 2013.

  1. Hey guys,

    Question - they sell you "high flow pipes" for your harley or sports bike or w/e.... But what stops me just taking off the muffler? That would be a straight through wouldn't it?

    Why would I purchase a set of straight throughs when I could do this? Whats the benefit?


     
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  2. I'm not totally up on the tech aspects, I'm sure someone will jump down my throat if I'm just a little bit wrong. But from what I can work out in order for the engine to run correctly the exhaust gases have to have a equal distance (for want of a better word) of escape.

    For example have a look at a V twin with a 2 into one exhaust, the rear exhaust pipe will have a an extra twist or 2 in order to get the right 'balance'.

    Oh and have you heard a HD with no pipes? Sounds crap....
     
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  3. Hmm I dunno man. Cause they try to flog you the vance and hines straight throughs... There is NO muffler in them at all and they a different "length" to the stock pipes - this is where my question comes in.
    Why are vance and hines straight throughs ok but just having no muffler isn't?

    Also the vance and hines straight throughs sound sexy as fcuk, so I figure it would sound the same without the mufflers?

    Just to clarify, I mean leaving the headers and pipe on, but just get rid of the restrictive mufflers and not replace them with anything.
     
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  4. Even though the Vance and Hines are a different length to the stock, you'll notice that the the rear pipe is the same length as the front pipe, yes?

    It has to do with air pressure.
     
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  5. Yeah you are right, both pipe are the same length.

    Im 90% sure that the header pipes on my bike are the same length as eachother too. If you take a look at the pick you will notice they are staggered and do no finish at the same point. (Was the same when I had the stock mulffers on too)
     
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  6. In my misspent youth, I tried this on various motorcycles and, while noisy as all hell, they typically ran like sick puppies.

    Apparently, there is some magical function, called "back pressure" which I have never understood, but, it seemed to work.

    Wee stubby open pipes don't provide this, while, st least some after market noisy exhausts do. (Shrug)

    Of course, wrt Harleys, it might be different.

    Normal engine design is based on producing HP, not noise. ;)
     
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  7. Which means the air travels the same distance under the same pressure.

    If the pipes were to end in line with each other then the pipe of the rear cylinder would have a loop or 2 in them.

    Have a look at the exhausts on a Buell.
     
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  8. The back pressure wave affects the performance of an engine, but there are plenty of hardleys out there with uneven length exhausts.

    Ideally you pipe length should be tuned, with consideration of the diameter, to the desired peak performance point of the bike.

    You can take them off, but they will get the attention of the cops. At least with aftermarket mufflers, or modified standards, you can make an argument with the cops.

    You will need to tune the bike to suite.

    And it may get fumy if you don't have the pipes far enough back. I'm not sure if bikes have exist point requirements. Looking at the buel, maybe not. Cars do.
     
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  9. i recon your already loud enough
     
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  10. The benefits of aftermarket mufflers usually are;

    look better, sound better, lighter in weight, more power.

    Just removing the baffles from the original mufflers without changing the external appearance, can sometimes work, but sometimes not and just sound crap. If your prepared to buy a new exhaust if it doesn't work, then what's there to loose in trying. The aftermarket pipe manufacturers might spend a bit of time designing their pipes to have a nice sound. They may just look like a straight piece of pipe to an untrained eye, but I'd bet that they sound much better than replacing the muffler with a straight length of exhaust tubing, or drilling holes in the standard muffler.
     
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  11. Worst case scenario, the hot exhaust gasses don't extract properly and you end up cooking the exhaust valves, overheating the engine and ruining the engine. All from having the wrong exhaust configuration.
    An exhaust system with a properly designed muffler will flow better than one with no muffler at all. This comes down to timing reflected pressure waves within the pipes such that they suck gasses out of the cylinders. Tuning involves getting the right balance between pipe length, pipe diameter, having sections of pipe stop suddenly rather than tapering into a larger section and anything that speeds up or slows down gas velocity. It's complicated stuff with tons of variables and the manufacturers do a pretty good job of making them work across a broad range of engine speeds with acceptable noise levels.
    Better peak horsepower usually comes at the expense of low RPM tractability whether it be from cam changes or more open pipes, or of noise ... often both. Other pipes deliver better better mid-range but the power curve drops off a little sooner.
    Just running open pipes can also make you a target of the cops and can earn you some nasty fines or even get your bike impounded if you really make a pest of yourself.
     
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    • Agree Agree x 2
  12. I'm wondering about this but for a different reason. On the Z1000 the slip on mufflers are after the main exhaust accumulator, so even with no pipes it doesn't sound much louder on the youtube videos. So why not remove them, just to save weight and clean up the look? From what I have read it makes no difference to mixture because it is after the cat and the accumulator/resonator.

    Would there be any issue with rain or water getting into the exhaust, or the hot gases corroding the exposed fitting and causing trouble later?
     
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  13. The term back pressure is a load of crap. Motors HATE back pressure. The most powerful motors on earth have 12 inch exhausts ( top fuelers ). Motors benefit from each exhaust pulse has a suction effect similar to a racing car slip stream behind it. That benefits by helping to suck the next puff of exhaust gas out of the cylinder.
     
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    • Agree Agree x 1
  14. I have two words for you: two stroke.

    High output naturally aspirated for stroke engines benefit from the same effect. Top fuellers are supercharged so don't benefit from it, they just turn the charger up if they want more air.
     
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  15. It's all about reflected pressure waves. The trick with designing a performance exhaust system, two or four stroke, is to get the positive pressure waves to reflect back up the pipe and bounce off the exhaust port just as the valve opens and form an area of negative pressure (which travels just behind the positive pressure wave as mentioned) ready to suck out the exhaust gasses. Then you want to get another pressure wave to do the same thing just as the intake opens (valve in a four stroke, port in a two) to help scavenge out the last of the exhaust gasses and pull in the fresh mixture. Anything that interrupts the system can leave hot gasses sitting in the exhaust port and overheat the valve, or even over-scavenge and pull too much unburnt mixture into the exhaust and do other kinds of damage by burning in the pipes. Two stroke engines with forced induction are particularly prone to the latter, but from the gasses being pushed rather than drawn through.
    It used to be an art getting the header lengths right to match the cam timing, and a black art to get expansion chambers the right size and shape to match port timing, but these days there are very good design models that take the guesswork out of the whole thing.
     
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  16. The V&H exhausts have concealed mufflers inside the pipe, they sell a quieter baffle as an option.
    Just pulling your mufflers might be good for drag racing but you will probably lose the usable street power, also everyone will think you are a bit of a wanker lol, too loud ;)
     
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  17. Yes the concept of a pressure wave is often misunderstood. Dark Angel is correct.

    You want the lowest back pressure you can get but still have the ideal pressure wave tuning.
     
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    • Agree Agree x 1
  18. Two stroke diesels like a bit of back pressure otherwise they just flow too much air through. Hence putting a turbo on them helps a lot where running up the supercharger does not add much benefit.
     
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  19. If youre really interested try this..
    remove pipes, headers included. Start bike. 5 seconds will be more than enough. put headers back on, Start bike again. see how long you can stand the noise. Grab some 1 3/4? inch (used to be) pipe and cut it so it looks long enough for a muffler, fit to bike then start, You can probably ride around the block without causing any damage, If the bike doesnt like it, go straight home. Put mufflers back on happy that you know why they put mufflers on the bloody things.
     
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  20. I wouldn't want to remove the headers/cat/resonator box, and with all those still in place the airflow, backpressure and sound seems to be much the same from the youtube videos and comments. So I'm just interested in the weight and space saving if they are left off...
     
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