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Thread: Lost RPMs?

  1. #1
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    Join Date
    Jun 2011
    Posts
    5

    Lost RPMs?

    Hi,

    I'm a new owner to a '98 SR24. I'm having speed and RPM issues.

    Engine - '04 496 H.O. with 150 hrs.
    Prop - 26" Bravo 1 four blade ss. Prop just scanned by Airmarine in Chicago and it is in good shape.
    Drive - Brave 1 with 1.50 gear ratio

    I do understand I am underpowered and will correct it in the future, but I am only pulling 4100 rpm's at 52/mph on gps.

    I had the throttle position sensor checked and at WOT it reads 99.8%, so that isn't the issue. The plugs were recently replaced. I have had no other engine scans done, yet.

    The boat gets on plane without an issue and the engine sounds healthy. I see no hull damage.

    I am going to try a 24" prop this weekend, but have been told that I should be able to turn the current one at 5,000 rpm.

    Most ads for this boat similarly powered claim top speeds of 70-75 mph. I figured with the current set up I'd at least be in the mid 60's. Any ideas?

    Thanks.

  2. #2
    Registered
    My Boats:
    htm sr24, 225hpTritoon & 04 33 daytona
    Join Date
    Sep 2003
    Location
    michigan
    Posts
    199
    What happened with the 24 pitch?

  3. #3
    Registered
    My Boats:
    HTM SR-24
    Join Date
    Jul 2009
    Location
    Cedar Springs,MI
    Posts
    71
    Just for referance...i ran a 475 hp 502 in my sr24 for a couple of months and i was seeing 76 gps @5400rpm with a 26 b1 prop and 1.5 gear.

  4. #4
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    Join Date
    Feb 2006
    Posts
    439
    I have a SR24 with a 496HO too,I ran a 26 bravo 1 at 4700 rpm and 1,50:1 top speed was 66 mph ,now I changed my regular 1,50 :1 bravo drive for a 1,26 :1 XR drive ,and tried a 22 pitch Bravo 1 prop ,and ran only 4600 rpm,I had no GPS to measure speed ,but it felt like it was a lot slower .
    Since there is no smaller Bravo 1 prop ,I am going to try a 21 Revolution 4 to see if this helps ,I have tried a lot more props ,Hydromotive Q4 and a Mirage ,but could not get the boat on plane due to prop ventilation .
    It seems like there is not enough bow lift from a Bravo 1 to lift the nose up in the air ,at least with this horsepower ..

  5. #5
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    Join Date
    Jun 2011
    Posts
    5
    Thanks for the responses. I ran the 24P this weekend and saw the rpm's go up to 4800-4900. Top speed went up to 60 on GPS. I did have four adults and two rather full tanks at the time.

    I feel like the load alone isn't enough to explain the speed differences between my boat and lucky cat's 76 mph or stirling's 66 with a 26P. Maybe I'm wrong?

    Oh yeah, I do have a tiny, tiny, tiny, ss hydrofoil stabilizer on the drive. Cale Carder at HTM2 said to leave it on. However, I wonder if it is scrubbing some rpm's and speed?

  6. #6
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    Join Date
    Feb 2006
    Posts
    439
    Next time you go out ,try to run the boat straith into the headwind (if there is any) you should see better speed ,the power we have is not enough to air out he tunnel,and let the boat run on its sponsons only .
    I had a regular bravo 1 1,50 before with the normal side water intakes ,and still had enough water pressure at WOT, the water intakes are even with the bottem of the tunnel ,the top 2 holes are above the tunnel ,thats indicates the tunnel is in full water .
    I bought the XR with low water pick ups only for bigger power ,that engine is a BBC 522 Ci with blower and intercooler and should make around 750 hp ,this must be enough to fully air the tunnel out

  7. #7
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    Join Date
    Jun 2011
    Posts
    5
    Thanks for the info. I did notice that when I hit some chop and got some air under the boat, I could feel the boat surge a bit. I'll just have to spend the off season working on more power.

  8. #8
    Registered
    My Boats:
    06 Eliminator Daytona 27'
    Join Date
    Jun 2006
    Location
    ILL
    Posts
    723
    Hey man this is Matt from Byron is this who I think it is? I got that 27' Daytona.

  9. #9
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    Join Date
    Jun 2011
    Posts
    5
    Hey Matt,

    Yes it's me. Got it runnin' as best as I think I am going to with this hull/engine/drive combination. Others with similar set ups seem to be getting about 10-15 more mph. I think all that is left is to dyno the engine and see if I am really getting 425hp. At the end of the day, I'll probably upgrade things this winter or next summer. Even if I did squeeze 70 mph out of the 496, this boat is begging for more power.

    I didn't want to bother you on my way out the other week.
    Hey........are you a dad again?

  10. #10
    Registered
    My Boats:
    06 Eliminator Daytona 27'
    Join Date
    Jun 2006
    Location
    ILL
    Posts
    723
    We need to hook up buddy!! Yes I am a new Dad haha up at the hospital still now! Baby girl Eva. 6lbs 4oz. PS Thank u for asking!!!
    Last edited by skydog; 06-17-2011 at 06:25 PM.


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