Engine RPM change if I rebuild a 96 to 103?

Discussion in 'Touring Models' started by gusotto, Sep 5, 2013.

  1. gusotto

    gusotto Junior Member

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    Over the weekend, I rented a 2013 Trike (103 engine) and noticed the RPM at 70 MPH was 3,000. Didn't get good gas mileage. Only 32 MPG.

    Then I took a 2007 Dyna (DLXR with a 103 engine) out for a test spin for my neighbor (70+ years young). He never had a Harley and wondered if it vibrated much.

    It also ran 3,000 RPM at 70 MPH.

    My 2007 Ultra w/96 engine turns 2,500 RPM at 70 MPH.
    Big difference!

    All three bikes have the 6-speed tranny. I'd think both 2007 bikes would have the same gearing.

    Question.....
    If I get the 96 upgraded to 103 by Harley, would my RPM at 70 MPH change? I don't need an extra 500 RPM change.
    Tough on the engine.
     
  2. Jennmarr

    Jennmarr Junior Member

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    No. Rpm will not change. Rpm at a given speed is a function of gear ratios not of CID.
     
  3. gusotto

    gusotto Junior Member

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    That is my thought but why would a 2007 w/103 engine have a higher RPM than my 2007 w/96 engine?
    Both have the same 6-speed tranny.
     
  4. Jennmarr

    Jennmarr Junior Member

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    The '07 you mentioned previously is a Dyna series bike, and the other was a trike. I assume they have a different final drive ratio than your ultra. I do not know what the MoCo used, but reduction of one or two teeth on the front (small) drive sprocket will have a significant impact on RPM at a given speed. I assume the trike is geared differently to more effectively handle the extra weight. Someone else can probably come up with the tooth count for each sprocket in the different applications you have mentioned. The old Evo powered touring bikes turned about 3000 rpms at 70mph.
     
  5. tourbox

    tourbox Senior Member

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    The Trike has a 30T & 70T final drive sprockets, The Dyna & Ultra both have a 32T & 66T final drive. I checked the clutch and compensator for the '07 Dyna & Ultra, they have the same P/N's so there gear/tooth count would be the same. The Trike has different P/N's.
    As to why the difference in the '07 rpm's I couldn't say unless when who ever did his 103 conversion they changed his final drive.
    tourbox
     
  6. gusotto

    gusotto Junior Member

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    I dropped by the dealership and my mistake.

    The Dyna is a 96 CI.
    I think I listened to the saleperson without checking the engine covers.
    Duhhhh...

    Still, it makes me wonder the difference between my '07 Ultra and the stock '07 Dyna.

    I do have a Power Commander on the Ultra.
    Wonder if that would make a difference?
     
  7. Breeze3at

    Breeze3at Well-Known Member

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    NO. ONLY gearing can make a RPM difference. A slight difference in tire size can make a difference, because that is part of gearing.
     
    Last edited: Sep 5, 2013
  8. btsom

    btsom Active Member

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    There can be slight differences in speed vs rpm with a change in tire size or aspect ratio BUT you will never see it unless you put in a speedo corrector. UNLESS a component in the drive line is changed which would alter the gear ratios, NOTHING you do to the engine will alter rpm vs speed. No magic spark plug, no magic PTFE lube, no tuner, no fuel pack, no air cleaner, no head pipe, muffler, no "big inch kit, or anything else will change rpm/speed. If you look in a service manual, and it might be in the owner's manual you can see the overall gear ratio for each gear. That ratio absolutely locks the rpm/speed for any gear you choose. You seem to be concerned with 6th gear so that is all I will talk about. If the overall ratio is 2.8 to 1 for 6th gear, the engine must turn 2.8 times to drive the rear wheel one complete revolution. There is NOTHING you can do to change that until you change one of the pieces in the drive line. If you see a difference from one bike to the next, take it as a matter of certitude that the drive lines are NOT identical.
     
  9. Rod Stewart

    Rod Stewart Active Member

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    I am not sure what the big deal is with it turning 3000 rpm at 70 mph?
    My 2004 Classic (big bored to 95") is exactly the same and its no big deal IMO.
    Now if you wanted to cruise at 95 mph, you would be turning 4000 rpm, and that may be a big deal after a while. As far as vibration goes it seems to me the faster these engines turn over, the smoother the ride!

    Rod
     
  10. gusotto

    gusotto Junior Member

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    The "big deal" is 500 RPM difference.
    The '07 Dyna ran 3,000 at 70 MPH.
    My '07 Ultra runs 2,500 at 70 MPH.

    I may have to check gear changes.
    Both bikes have 6-speed trannys.