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Damage for riding with no muffler?

Discussion in 'Technical and Troubleshooting Torque' started by tonee, Jan 3, 2012.

  1. I want to be a douche and ride around with the pipes off on the VFR just because it sounds like a mad V8 without the pipes.

    I've heard something about the back pressure and so forth which is not good. However the catalytic converter isn't inside the muffler so would that still produce sufficient back pressure?

    Don't flame me on my ignorance yet, just want to learn before I do anything stupid...well to the engine at least.
  2. Don't make a habit of it.
    A small ride will not do much at all except annoy everyone around you.
  3. Complex question - simple answer. Smee's right.

    Open pipes won't hurt a properly tuned engine. If you knew you were going to run it in that state long term - like maybe you were building a race motor - you might change the cam timing slightly to take more or less advantage from the pressure pulses and the overlap, so as to avoid sucking heaps of unburnt mixture straight through the chamber without burning it. That's bad for emissions and for fuel economy and efficiency. But even in the medium term, it wouldn't do a whole lot of damage. It might make the motor more likely to throw flames and stuff out the pipe, as you sometimes see in V8 supercars for this (these) very reasons.

    If your curiosity provoked you to go the extra step and remove the pipes altogether - at the cylinder head - you'd notice two things. The noise level is high enough to cause pain and serious hearing loss very quickly. Large industrialised nations will declare war on you in minutes, not hours, and you could well burn your exhaust valves out quite quickly. An open pipe is not the same as no pipe. With no pipe, fresh oxygen can get back at the valve and port while hot gasses are coming out, re-igniting and re-energising the combustion process and adding greatly to the heat on the exhaust valve and port. Oddly enough, a similar thing can happen with a fairly small leak in the header or the manifold - head gasket. (Yes, cars have those, but bikes do have a collar that holds the pipe on, retained by studs or sometimes springs.) If that joint leaks, you'll hear a sound like a lose tappet or valve clearance, but it will come and go in proportion to throttle position. If you get a crack in the header, or that joint leaks, fix it.

    Check out the header stubs on a Spitfire or Hurricane - or anything else Merlin powered. From memory, those are about 6 inches from exhaust valve to exit. Any shorter than that and the valves burned. Sodium filled valves with screw in phosphor-bronze sintered metal guides, some of the trickest materials technology in the world when they were developed in the mid 1930s.
    • Like Like x 1
  4. Thanks for the thorough answer kneedragon.

    I just wanted to ride to my mates house without it on, so I guess that'd just give me a slight drop in power and fuel efficiency.
  5. ... probably offset by the weight reduction. It'll draw you to the attention of every officious person within earshot, though. And it will expand the radius of earshot quite a bit.
  6. and don't forget the risk of any police officer within hearing distance defecting your bike upon hearing it.
  7. Do it. Everyone should do it at least once.
  8. You may find that you have a huuuugge mid-range flat spot. Depends on whether your EFI can cope with the change or not. Carbed engines will certainly lose performance.
  9. post video this shall be good
  10. Had to read that twice, thought you said 'defecating on your bike'...
  11. Do it and go for a ride up and down Maroondah Highway in Ringwood at 5am.. I heard that they REALLY love it down there...
  12. #12 tonee, Jan 4, 2012
    Last edited by a moderator: Jul 13, 2015
  13. deleted
  14. Do it. While not sounding as good as the Viffer in that vid I'm lead to believe the CB400 sounds decent de-piped also ;)