25' senza spectre 52mph at WOT 4400rpms 23p 4 blade 515hp something is wrong...
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25' senza spectre 52mph at WOT 4400rpms 23p 4 blade 515hp something is wrong...

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    Default 25' senza spectre 52mph at WOT 4400rpms 23p 4 blade 515hp something is wrong...

    I have a larson senza spectre 25' with a brand new 515hp 454 mercruiser. It is 4400rpms at WOT, has a 23p 4 blade stainless prop. Other people are getting 65 mph plus with this boat with less hp. What gives? I get 52mph on gps! Any help woukld be appreciated.

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    Quote Originally Posted by project tt View Post
    I have a larson senza spectre 25' with a brand new 515hp 454 mercruiser. It is 4400rpms at WOT, has a 23p 4 blade stainless prop. Other people are getting 65 mph plus with this boat with less hp. What gives? I get 52mph on gps! Any help woukld be appreciated.
    What altitude to you run at? Where are you located?

    My 425-430hp spins a 24P 4-blade at 5000 in a 30-footer, but I am always near sea-level.

    You would be way down on HP to only be spinning a 23 to 4400 in a 25' boat. My guess is you are at about 4,000 feet altitude?
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    i am 455 feet above sea level. Watkins Glen, NY. What do you mean way under hp?

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    Quote Originally Posted by project tt View Post
    i am 455 feet above sea level. Watkins Glen, NY. What do you mean way under hp?
    Well, at 455 feet, you're no different than around here. So, altitude is not the theft of HP.

    What I mean is - if you are supposed to be a TRUE 515hp and only swinging a 23P to 4400 - you are way down on HP. Like, down to 300.

    I am assuming this is a carbureted motor? Either way, is WOT actually occuring? With the engine OFF, smack the throttle wide-open. Look at the butterfly(ies) and make sure they are WO. You can even disconnect the cable at the carb/TB and see if they both line up at WOT.

    If the motor has been out of the boat recently / recently installed, this is probably your problem.

    Again, the reason I say you are down hp (or limited throttle) - is because I have nothing special for a motor and swing a 24P 4-blade to almost redline (5000 vs. 5150), which has my 30-footer at 62-65 up on the steps. There's no reason your 25-footer shouldn't be at redline with that 23 and 500+ hp.

    BTW, 515hp 454 Mercruiser? Is it the supercharged older carbureted 525SC? Even the later NA 502-derivative was 415hp. The alum-head later 502s are 525hp (HP525).

    Are we sure it's a 1.5 gear-set in the drive?

    Friends of mine with a 25-foot Shockwave have my same motor (425-ish hp). They have more restrictive exhaust (long S-pipes and full-time mufflers) and they STILL spin a 23p 4-blade to 5000.

    I am beginning to think you have a 330hp 454 mercruiser? 385hp 454-Mag?
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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