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Thread: underproped 540 ci

  1. #1
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    underproped 540 ci

    I just got my 22 classic back had a new 540 v4 2017 engine put in to replace a 7.4 liter, tried a 27 pitch bravo 1 prop hit the rev limiter right away someone suggested a four blade 28 pitch prop any suggestions out there the 540 is rated at 505 hp when reflashed to the 5200 rpm limit

  2. #2
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    If you gather solid observations of your gear ratio, GPS speed right before you hit the rev limiter, and RPM at that speed just before you hit the rev limiter (5200?), it'll give a much better idea of what props will do well for you. Especially if you can do it with a light load and with the boat trimmed out nicely for speed. From your description with that 27" 4-blade Bravo1, not sure a 28" is enough.

    (If you don't have a GPS, you can download a GPS speed app for your phone.)

    Sounds like it's really running though, congrats.
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

  3. #3
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    The thunderbolt V module on that engine is not adjustable and can not be re-flashed to my knowledge?? It does have a rev limit and and is set 50 rpm above the max rpm which I believe is 4600 on that motor.
    Did you get any gps speed?
    Rated 'R'
    Raw Rowdy & Rockin

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    In one of Mercury's test , on a Baja 275 , the engine rpm was at 4800 at top speed. I wonder where the rev limiter is actually set being that the rated range is 4200-4600 rpm.
    better to die on your feet, than live on your knees

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    Quote Originally Posted by smokediver View Post
    In one of Mercury's test , on a Baja 275 , the engine rpm was at 4800 at top speed. I wonder where the rev limiter is actually set being that the rated range is 4200-4600 rpm.
    I noticed that too on the Baja test of the Merc Reman 540. They definitely didn't have the right prop on it. Given it's a carb motor, I was thinking it wouldn't even have a rev limiter. But regardless, to your point, i can't imagine running one of those anywhere near 5200. It'd have to be a very different 540 build. Not sure exactly what motor Myron has, in this instance.

    Myron, what motor is it?

    (I had a 310 hp EFI 454 that was rated for 4200-4600 wot. Wide open with a light load it ran at 4550 or so. (Actually didn't change much with load.). If I had another motor with that sort of behavior, I might even prop it closer to 4400 -4450 with a light load.)
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

  6. #6
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    I put a custom built 540ci/625hp w/ Merc XR Speedmaster/ Imco -2" shorty in my 22C and spent a lot of time messing with it and trying different props. I found a 28p 4 blade Bravo 1 handled much better and also went faster than with my 3 blade Hydromotive 28p. The 28p Bravo 1 ran a solid 80 @ 5,500 but was bumping my limiter. I then tried a 30p Bravo 1 and also ran 80, but at 5,100 with room to grow. I'm liking the 30p Bravo 1 for my boat for now.

    Not sure the speeds or hp you're running, but I'm guessing a 28p Bravo 1 is a pretty good start.
    The four blades like to be trimmed way out to get the speed. This makes the drive and boat go into a slight oscillating yaw which can be a little disconcerting. The cure for that is external hydraulic rams. - That's my next move.

    Good luck!

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