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Thread: Outdrive Gear Ratio

  1. #1
    Run_em_Hard
    Is there a quick way to check your ratio? Bravo 1 with IMCO gears.

  2. #2
    RiverToysJas
    In theory......if you can see the coupler, you can turn the prop and see how many times the coupler goes around. One and a half, one and a third....etc.... I think it'll work....but I just pulled that out of my butt so who knows.
    RTJas

  3. #3
    ToMorrow44
    Give us some info on your boat (motor, drive, speed, prop size, etc) and I bet we can figure it out.
    -Tom

  4. #4
    BDMar
    Just a little FYI.... Imco as well as everyone that builds a Bravo l uses Mercury gears. If they are XR gears the ratio is changed in the lower so you cant just remove the top cap and count the teeth. Remove the spark plugs, mark the damper, have someone rotate the engine by hand keeping good count while you count the propeller revolutions. I would rotate the engine exactly 10 times then compare that with the propeller rotations. The most common ratios for XR gears are 1.50:1 and 1.35:1. Standard Bravo l ratios are 1.50:1 and 1.36:1.

  5. #5
    Run_em_Hard
    Just a little FYI.... Imco as well as everyone that builds a Bravo l uses Mercury gears. If they are XR gears the ratio is changed in the lower so you cant just remove the top cap and count the teeth. Remove the spark plugs, mark the damper, have someone rotate the engine by hand keeping good count while you count the propeller revolutions. I would rotate the engine exactly 10 times then compare that with the propeller rotations. The most common ratios for XR gears are 1.50:1 and 1.35:1. Standard Bravo l ratios are 1.50:1 and 1.36:1.
    I will have to give this a shot this weekend.

  6. #6
    Run_em_Hard
    I put a new outdrive on this past winter the the guy I bought it from said it was 1.5 gears. I am having a hard time hitting my RPM's. The motor is running sweet, just not getting all the way there.

  7. #7
    uselessgrant
    seems to me that the ratio on a bravo 1 is stamped on it somewhere on top. not sure where though

  8. #8
    Racey
    What size prop and how fast do you run, the Gear ratios are all Under-Drive, usually 1.36's run 22-24 pitch in 4 blade, 1.5's run up to 30 pitch, these are for 75-85 mph boats, Generally speaking of course.

  9. #9
    BDMar
    seems to me that the ratio on a bravo 1 is stamped on it somewhere on top. not sure where though
    That is true, however he mentioned that the gears have been changed.....

  10. #10
    shockwaveharry
    Try plugging your numbers into a prop slip calculator like the one on BAM Marine's site. If you know your prop pitch, top speed and at what rpm's it happens, it should be apparent when you plug in different gear ratios. For example, if you're going 70mph at 5000rpm's and spinning a 24 pitch prop, you probably have 1.5's. If you're prop is a 22 with the same speed and rpm, than you probably have 1.35's.
    It's not the surest way, but at least you won't get your hands dirty.

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