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What pitch/PN SpitFire prop for new 50hp 4stroke on Tracker Pro 170???

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  • What pitch/PN SpitFire prop for new 50hp 4stroke on Tracker Pro 170???

    I have "heard" they say same pitch as original 3 blade but I'd like to gain MPH on the top-end so I wondered if a pitch change was warranted when going from 3 blade OEM black max to 4 blade spitfire??? With the OEM 3-blad the boat will run 6k RPM max and about 34-36mph depending on conditions.

  • #2
    A 4 blade is usually slower than a 3 but it handles better.
    When in doubt,Trim it out!!!
    Business Owner & Certifed Technician
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    • #3
      Unless you have a need to get absolute max performance from your engine, I would slow it down a little, to something closer to 54-5500. I doubt it would cost you much in the way of speed (you may even pick up a mile an hour or 2), but you may notice a very slight loss out of the hole.

      For your trouble you'll get an engine that doesn't sound near as busy at wide open throttle. Unlike 2 strokes that like rpms, 4 strokes are about torque. Dropping your rpm's a bit can help you take better advantage of that. That's been my experience with them anyway.

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      • #4
        First things first. Boat is 980#. transom is 22.5". All I've seen from the factory have the engine mounted too low for best speed performance. An adjustable 4" jack plate would make that a lot easier. Get that right before changing props. it can make up to 20% difference in speed and fuel efficiency. Max prop I'd use is 13P, unless you want to remove the restricter plate to increase HP from 50 to 60, then a max of 14P. Proped like this you should turn ~5500rpm. With a 50hp, you should be able to get ~36 mph with a 13P prop, and close to 40 mph with a 60hp and 14P prop.. With the engine mounted low and a 50hp engine, you'll be lucky to see 31 mph with a 12P prop and trimming it up will cause excessive porpoising. I went through this with a 995# Lowe Stinger 175 with a 60hp 4s. yor boat is about the same weight. Without mods just use a 12P prop.

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        • #5
          Installing a jack plate, when one can simply adjust the height of the engine on the transom, is questionable advise. It's one thing when you would need to set the height differently on a frequent basis (for fishing in the shallows/flats for instance), but quite another to just set the engine up properly on a one time basis. Many might view the added expense of a jack plate as a waste of money.

          Regarding a "restricter plate" we'd need to know what engine we're talking about. I KNOW Honda doesn't use one as I'm very familiar with them. If the brand you're thinking of does does use one, I'd be curious about the part number as I think most of these removeable restrictor plate stories were born in fantasy land.

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          • #6
            An adjustable jack plate for up to 125hp engines goes for about $125. And that's about what it cost for a dealer to remount the engine. And while the manufacturer Paid to have mine raised up, If I ever change engines, then it will get one since once installed, there's no need to reseal mount bolts in the hull or pay to have the engine height changed ever again.
            I assumed he has Mercury 4S engine,and like the Yamaha 50hp , I'm pretty sure it has a restricter plate. I'm also pretty sure it uses the same ecm for both the 50-60hp engines.

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            • #7
              At speeds below 45 - 50 mph there isn't much to gain at jacking/raising the engine up, unless of course the wrong was hung on in the first place. at speeds higher than mention earlier, raising the engine one inch will usually increase top speed by 1 mph, reduce chinewalking, and reduce reduce the ability to raise the bow with the power trim.

              Years ago many people were convinced that when two or more engines in the line up had the same displacement, the only difference was a jet change and it was more HP. Well there were many differences. some little, some not so little between the different HPs. Fast Forward to a few years later(sounds like the Lyrics of an Alanis Morissette song) and its, Restrictor Plates, and maybe a ECM. Again maybe little differences maybe not so little difference, some not actually visable.

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              • #8
                I agree Jimmbo, but to this day "restrictor plates" are still discussed, and I think they're an internet myth. I hate to see people wasting their time trying to get more info on them.

                Honda 35, 40, 45, 50, and 60 hp engines all share the same short block (block, crank, rods, and pistons). The heads, which also carries the cam, I suspect are just slightly different, with the differences not visible to the naked eye - only by a coded dab of white paint. They use the same intake manifolds (other than the injected 60). The 35. 40, 45, and 50hp carbs, which also appear identical, may also have some very slight differences, though they share the same gasket kits! ECM's I have no idea. On these engines, as well as the 75/90 4 cylinder engines that are set up nearly identical like the 3 cylinder engines, there is NO restrictor plate!

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                • #9
                  Originally posted by jimmbo View Post
                  At speeds below 45 - 50 mph there isn't much to gain at jacking/raising the engine up, unless of course the wrong was hung on in the first place. at speeds higher than mention earlier, raising the engine one inch will usually increase top speed by 1 mph, reduce chine walking, and reduce reduce the ability to raise the bow with the power trim.
                  Prior to raising my 60hp 4s on my new boat I couldn't get over 35mph without looking like a porpoise going through the water and getting beat to death when the bow slammed back down. After raising it just 1.5" I could get a good 38 mph without any porpoising and max speed with just slight porpoising. I don't know why you keep saying it doesn't matter much because that's just bs. The point is most are likely hung wrong from the factory. Mine was and even the rep at the manufacturer agreed. That's why they actually paid the dealer to have it raised. Had I not done a lot of research and testing, I'd still be left with an under performing boat. A change in prop and engine height got me from an original 31 mph to 40 mph with the same boat and engine.

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                  • #10
                    See item 21 - Restrictor for 50hp.
                    https://public-mercurymarine.sysonli...=englangDB=eng

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                    • #11
                      Wes, there's a user name and password required at that link. Maybe you could identify that part here on I Boats? -Al

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                      • #12
                        Try this, then select your engine- intake manifold.
                        https://www.mercurymarine.com/en/us/.../parts-catalog

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                        • #13
                          Before I go wasting a bunch of my time looking at parts diagrams for 20 different engines, maybe you could supply more info about what engine I'm supposed to be looking at/for, to narrow things down a bit?

                          I'll post my findings with a link to info here on iBoats. -Al

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                          • #14
                            I was looking at the 50 hp efi 4s, as I assume that's what he had. But you can also look at many of them. Lots of them have restrictor plates in the intake manifold. They even show one in the drawing for the 60hp but it notes for the 50hp on the side.. It's not that hard to find.Only took a couple of minutes. Go to mercury website, select Parts and acc., slect parts catalog, select launch it, click on outboards, slect engine, select intake manifold. You can download the section as a pdf. I don't see a way to attach it here or I would.

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                            • #15
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                              OK, part found here, #24
                              https://www.**********/catalog/mercur...ntake-manifold

                              So we see that the 40 and 50HP MERCURY 4 stroke EFI engines have a restrictor plate, but it remains to be seen what you may have if it's removed. Fuel mixture, ign. timing, cam timing, ECM, etc, may also be in play here. -Al

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