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502 Mag MPI Bravo One gear ratio???

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  • 502 Mag MPI Bravo One gear ratio???

    How can I determine the gear ratio in a Bravo One drive I'm looking at? I have a partial serial number but could not read the gear ratio decal on the side of the drive.

    It's in a 1982 26' SeaRay Sundancer with a 454 Mag. and has a 17" pitch stainless prop...if that helps.
    sigpic

    1990 Sea Ray 220 Cuddy Merc 5.7 Alpha
    1986 Sea Ox 230WA 225 Evinrude

    \o/ Gal. 2:20 \o/


  • #2
    Re: 502 Mag MPI Bravo One gear ratio???

    If the drive you are looking at is a 1982 model, it's not a Bravo. Bravo drives didn't come out till late 88. It's probably a TR or TRS, and you can't use it with your Bravo transom shield.
    Don S.

    sigpic

    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

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    • #3
      Re: 502 Mag MPI Bravo One gear ratio???

      The boat is an 82, the Bravo drive is a much later model. It was re-powered at some point with the 454 Mag/Bravo setup. i'm just trying to determine the gear ratio for compatibility with my 98' 350Mag. How big of a deal is gear ratio? Can it be overcome by prop pitch/diameter?
      sigpic

      1990 Sea Ray 220 Cuddy Merc 5.7 Alpha
      1986 Sea Ox 230WA 225 Evinrude

      \o/ Gal. 2:20 \o/

      Comment



      • #4
        Re: 502 Mag MPI Bravo One gear ratio???

        Take the cover off the top of the driveshaft housing and count the teeth on the top gear. If the gear has 30 teeth, it's a 1:65, if it has 32 teeth it's a 1.5 and if it has 29 teeth, it's a 1.36. You only need a 3/8" twelve point socket to remove the 4 bolts. Some oil may leak out though.

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        • #5
          Re: 502 Mag MPI Bravo One gear ratio???

          Originally posted by 1kwik72 View Post
          The boat is an 82, the Bravo drive is a much later model. It was re-powered at some point with the 454 Mag/Bravo setup. i'm just trying to determine the gear ratio for compatibility with my 98' 350Mag. How big of a deal is gear ratio? Can it be overcome by prop pitch/diameter?
          The difference between a 502/454MAG and a 350 is huge. I think a drive ratio change and a prop change would be the correct approach. Used Bravo driveshaft housings are not hard to find. I got a rebuilt (still had assembly lube on the gears) 1:5 unit on craigslist for $500 last Spring and it has performed flawlessly. You can simply sell yours when you find what you want. From what I gathered, the lower number ratio drives were more desireable and you need a higher number so that should make getting a replacement easier.

          The driveshaft housings are the same on Bravo 1s, 2s and 3s, but the final gear ratios are different on the Bravo 2s and 3s due to different gearing at the propshaft. 30 teethy on a B2 or B3 gives a 2.2:1 ratio, 32 teeth gives a 2.0:1 ratio and 29 teeth gives a 1.81:1 ratio. So if you find a B2 or B3 driveshaft housing, you'll know what to look for.

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          • #6
            Re: 502 Mag MPI Bravo One gear ratio???

            Thanks for the advice!!! I'm assuming that I need a 1.5 ratio ideally...is that correct?
            sigpic

            1990 Sea Ray 220 Cuddy Merc 5.7 Alpha
            1986 Sea Ox 230WA 225 Evinrude

            \o/ Gal. 2:20 \o/

            Comment



            • #7
              Re: 502 Mag MPI Bravo One gear ratio???

              Sorry, its going in an 84 22' sea ray cuddy.
              sigpic

              1990 Sea Ray 220 Cuddy Merc 5.7 Alpha
              1986 Sea Ox 230WA 225 Evinrude

              \o/ Gal. 2:20 \o/

              Comment



              • #8
                Re: 502 Mag MPI Bravo One gear ratio???

                The 350 Mag MPI and the 502 Mag MPI both used the 1.5:1 gear ratio.
                Don S.

                sigpic

                Please, no PM's (Private Messages) regarding boat/engine problems.
                That is what the forums are for.
                Only forum/moderator issues will be answered in PM's.

                Comment



                • #9
                  Re: 502 Mag MPI Bravo One gear ratio???

                  Originally posted by 1kwik72 View Post
                  Sorry, its going in an 84 22' sea ray cuddy.
                  A 1.5 drive with a 17" prop and 10% slip would give you about 48 MPH at 5000 RPM. A 1.36 drive with same prop, slip and RPM would give you about 53 MPH. I'm thinking the 1.5 is the better bet. If you end up under-propped, it's really easy to go up from 17". If you are over-propped with the 17", going down in pitch is going to be tougher since there are fewer props available in <17" than there are in >17"

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                  • #10
                    Re: 502 Mag MPI Bravo One gear ratio???

                    With the 350 Mag, you are going to want the 1.5 ratio, the 1.36 was an option for the 502, but for the 350.

                    Attached Files
                    Don S.

                    sigpic

                    Please, no PM's (Private Messages) regarding boat/engine problems.
                    That is what the forums are for.
                    Only forum/moderator issues will be answered in PM's.

                    Comment



                    • #11
                      Re: 502 Mag MPI Bravo One gear ratio???

                      Don and Mischief Managed, thank you SO much! This is great information! I'll be getting this drive setup for my boat...you guys just saved me about $4,000!!!
                      My old Sea Ray cuddy should be moving much faster this season!
                      sigpic

                      1990 Sea Ray 220 Cuddy Merc 5.7 Alpha
                      1986 Sea Ox 230WA 225 Evinrude

                      \o/ Gal. 2:20 \o/

                      Comment



                      • #12
                        Re: 502 Mag MPI Bravo One gear ratio???

                        A 1.5 drive with a 17" prop and 10% slip would give you about 48 MPH at 5000 RPM.
                        That engine and drive will work nice in that boat.

                        You'll probably be capable of turning a 21-23p (stainless 3 blade) prop With a 502......
                        I wouldn't count on 10% slip though.....expect more like 12-15%

                        That boat would perform better with a Bravo III
                        ----------------------------------------------------------------------------------
                        I use xxx oil and have never had a problem........
                        This post was created with OpenSuSE x64 Linux!

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