08 Ultra Exhaust Question

Discussion in 'Touring Models' started by ultra pearl, Jan 31, 2011.

  1. ultra pearl

    ultra pearl Member

    Can I install Screaming Eagle Street Performance Slip-on mufflers on my '08 stock Ultra, without changing the air intake or fuel injection set up from factory?
  2. Dr. Dolittle

    Dr. Dolittle Experienced Member Contributor Retired Moderators

    You can, but.....

    Your bike is already running lean straight from the factory. New slip ons will make this situation a bit worse. Debatable what the long term engine effects will be but why take a chance? Dozens of fuel controllers to correct the lean situation are available, depending on your budget and the level of complexity you want.
  3. ultra pearl

    ultra pearl Member

    Thanks Dr. I guess I was in-correctly informed that if you installed slip-ons and let the bike idle for 15 minutes it would remap itself to the new mufflers.

    I'm a new Harley owner, forgive my lack of knowledge.
  4. Iceman24

    Iceman24 Well-Known Member

  5. flh canuck

    flh canuck Active Member

    Your fuel injection ecm will compensate for some modifications to a degree (at least in closed loop mode) but as the good Dr. says, the engine is already pretty lean from the get-go.

    Reducing back-pressure by going to a free flowing exhaust will simply lean things out even more depending on which pipes you go with.

    At very least, I would suggest getting the stage one ecm down-load if you change out the pipes.

    Mine ran well with just the down-load however I am awaiting the arrival of my new screamin eagle pro-tuner as I have a few more changes in the works and this will allow me to adjust the factory ecm without relying on the dealer.
  6. rsauder

    rsauder New Member

    I swiched my 08 Ultra last summer with screamin eagle pipes . Runs better and better fuel mileage. Didnt have to do any downloads either. :newsmile01:
  7. TheBoss

    TheBoss Banned

    I don't see how adding the SE slips only will worsen the factory lean condition. Same amount of intake air and same amount of fuel added. Same AF ratio.
  8. ron1978

    ron1978 Active Member

    i added true duals, with oval dresser pipes, fuel pack- and heavy breather, and had stage 1 download, bike gets 33-35 mpg thats it, all my friends that are stock are getting 43+ mpg, just little info on upgrades
  9. Fatboy 07

    Fatboy 07 Member

    ron1978, I have upgraded my 2008 Ultra to a 103" w/SE 259E cams, 10.5:1 pistons, HP Bee-Hive valve springs, SE A/C, SEPST, with stock heads, and get 42 mpg regularly. My sweet spot for mileage is 2800 - 2900 in fifth gear (best mileage) and dyno's at 93HP and 109 ftlbs of torque. I have only lost about 2 mpg going from stock to the above. Must be because the engine does not have to work as hard at any given gear/rpm.
  10. flh canuck

    flh canuck Active Member

    Its all about volumetric efficiency my friend.

    Any time you alter the Harley Davidson engine whether it be free flowing exhaust, intake or cams, you alter the volumetric efficiency or amount of air that the engine is able to pump through at any given rpm.

    Free flowing exhaust reduces back-pressure which allows spent gasses to flow out of the engine easier, thus the engine is able to flow more air into the engine compared to the air flow with a stock exhaust.

    The fuel injection system used by Harley Davidson is essentially a speed-density type system.

    In simplified terms, it works like this:

    Based on a given intake and exhaust system, if the air temperature and pressure is this number, the throttle position is at this angle, and the engine is at this rpm, according to the look-up tables or calibration inside the ecm, there must be this much air flowing into the engine therefore it needs this much fuel.

    This would be considered open-loop mode when fuel metering is based solely on sensor inputs and look-up tables and the ecm is not using feed back from the o2 sensors to monitor where the actual fuel ratio is at.

    In closed loop, the ecm does all these same calculations based on sensor inputs and look-up tables but then is able to see how close it is actually getting the fuel mixture and make small adjustments as needed based on the feed-back from the o2 sensors.

    I am still learning about the Delphi system used on Harley Davidsons and could be wrong but I believe the engine typically only operates in closed loop during part to mid throttle cruise conditions.

    By re-flashing the ecm, you can change the look-up tables or calibration so that the ecm calculates fuel flow for the correct volume of air going through your engine based on the type of air intake, exhaust system etc. that is installed on your motorcycle.

    True, just adding slip on mufflers should not impact air-flow to the same degree that adding a stage one air intake system would, but even small changes in air-flow will throw the calibration tables off, especially when the factory calibration is already on the lean side in order to comply with epa regulations.

    Again, this is a bit of a simplified analogy but hope it makes sense and takes some of the mystery out of fuel injection. Cheers!:D
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