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Replace airbox with 4 smaller filters - efi bike. What to watch for ?

Discussion in 'Technical and Troubleshooting Torque' started by bennjamin, Apr 6, 2010.

  1. Hey everyone

    I have a Honda cb400 , naked and want to clean up the look / keep it like a cafe racer and simply want to remove the airbox and replace with 4 smaller filters.
    On a efi bike , should the ecu trim fuel and not lean too much ?
    I intend to replace the muffler soon too.
    Does replacing the box cause issues with the pcv system or evaporate system ?

    Any thoughts thanks

  2. It depends on whether the efi sensor can monitor for changes in airflow & alter the air/fuel ratio. I would suspect not on that bike, but maybe it can...?

    Have a chat to a dealer perhaps.
  3. Why do you want to replace it with 4 smaller filters? NA engines should have tuned resonance airboxes to help with mid range torque.

    I doubt youre going to do this, but put the bike on a dyno and youll be suprised at the power gains (or losses) of some mods.

  4. good question - its purely for intake noise/look as i like the cafe/classic look.
    Im more than likely expecting no gain or even loss ( perhaps a shift in power band ) As for dynoíng that would be interesting and worthwhile the extra $100 or so for two runs back to back
  5. The vast majority of EFI bikes will have a MAP (Manifold Air Pressure) sensor living inside the airbox.

    I'm not sure what would happen if you deleted the airbox and the MAP sensor on an otherwise unmodified bike.

    It might respond gracefully and ignore the obviously-faulty readings. It might respond by not running at all. It might incorrectly assume the readings are correct and do really strange things to the fuel and ignition timing.

    We tuned our CBR600F4i motor with a MoTeC ECU so that it would run using only throttle position, revs and air temperature, but that's not ideal (air pressure and density fluctuates with altitude, weather, etc).
  6. Yes you are technically eliminating the pollution gear if your remove the pcv return hose. You'll need to put a breather or a catch can on it - dont just block it off. It will make the bike smell of oil.