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Stock exhaust Butterfly

Discussion in 'Motorcycle Tech Talk' started by JST, Jun 27, 2007.

  1. JST

    JST New Member

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    Hi Guys,
    I have just brought my first Harley ( after 32 years of Japanese bikes ) its a 2007 FLSTC 96 cube Softail, I have replaced the stock Catalytic slip on mufflers and put on a set of aftermarket ( I live in the UK ) I noticed that there is a spring loaded cable operated butterfly valve located in the back cylinder header pipe just up from the muffler, I imagine this is an emissions flap, my question is, can I just disconnect the little servo cable and wire the flap in the open position relieving the backpressure on the rear cylinder.
    JST, Jun 27, 2007
    #1
  3. kenfuzed

    kenfuzed Administrator Staff Member

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    The actuator flap is new for 2007 Harleys. You could disconnect it but unfortunately unplugging the servo generates an error code. Same goes for the intake solenoid if replacing your aircleaner and unplugging that servo. There are some terminator plugs available for each of these which plug in and eliminate any error codes. Once I find out more about it I'll post it here.

    An interesting side bit, the actuated flap when used on a cross-over (i.e. touring duals) is an idea thats been floating around for a few years and is actually a great performance boost. At idle and low load the flap remains almost closed, diverting exhaust into a single muffler and reduces cooler air from being drawn back up into the head pipes from the unused side. Once you wack on the throttle the valve opens wide and uses both outlets for maximum power. I actually experimented with a similar idea a while back using a one-way flap, but I never could overcome the chatter without fabricating some sort of spring. I'm hesitant to discount these factory actuators as something that inhibits performance until more is known about them. This may be a rare case where an emissions device could also be good for performance.
    kenfuzed, Jun 27, 2007
    #2
  4. chucktx

    chucktx Moderator Staff Member

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    interesting ken......thanks. sort of sounds like something out of the 60's, when cutouts were popular.....the cable controled ones......hmmmmmm
    chucktx, Jun 28, 2007
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  5. ironhorse

    ironhorse Active Member

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    I didn't ever think of the cold air draw that makes sense
    ironhorse, Jun 28, 2007
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  6. JST

    JST New Member

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    Thanks for that Ken,
    I do follow your logic, but carn't help the doubts in the back of my mind that the emmission boys when they designed this had the word performance handcuffed up in the corner in a dark room... Do you think that at partial throttle openings the low exhaust gas velocity from each individual header hitting there own catalytic converters is not enought to get both the converters up to ther optimum efficient operating tempreatures so they direct both header gases into one to achieve this and get there required emmission controls at partial throttle openings, there as you have pointed out
    comes a point when the ECU opens up the butterfly as the velocity has increased enough to have both CATs operating efficiently, and knowing the emission boys this would be at a point higher up the rev band to ensure there requirements were met but on our point probably hurting us with excess backpressure in the rear cylinder, I would like to run a couple of dyno runs just to test this with the flap operating normally and with it wired open... especially since I have dumped the CATs.
    JST, Jun 28, 2007
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  7. kenfuzed

    kenfuzed Administrator Staff Member

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    I as well would really like to see some dyno charts and real world testing on this set up. The whole thing is still very new to everyone, but give it till next year and you'll see plenty of talk about this. Personally I'm gonna remain the devils advocate on this one until I see more data. I did some of my early automotive training with California emmisions and learned early on that flow restrictions are often more of a misconception when it comes to regular street driving. I've seen my fair share of vehicles that suffered horribly by stripping down to a non-emissions vehicle. The result would be great wide open throttle performance but a dog anywhere down where most people actually drive. However thats not to say that I'm a big fan of CATs on motorcycles either.

    I'm really interested in hearing and seeing more about the 07 exhaust systems. I still have plans myself to upgrade to a new bike in the near future, which may become another guinea pig... since I've never been able to leave stuff alone :D
    kenfuzed, Jun 28, 2007
    #6

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