newbie to prop sizing
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newbie to prop sizing

  1. #1
    Senior Member Mrs.HLB's Avatar
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    Default newbie to prop sizing

    looking at a lavey xtski 21 has 454 mag with imco powerflow standard stainless short riser boat is proped with a 22 4blade current owner says it hits the rev limiter.

    He has a 26 4blade labbed and says it is not fuel efficient and tough to come out of the hole.

    When i tested the boat I was on puddingstone lake 35mph speed limit so no WOT passes with the 22 to confirm his statement of hitting the rev limiter.However it did come right up on plane and worked well @ 35mph. He did say however that the 26 labbed was gps'd at 5100 rpm @ 76 mph that is a little less than 10% slipage. I have seen tests where this is possable but usually not the norm. I also thought that 5150 was the top RPM for the 454mag F/I 385 hp

    With imco power flow exhaust only will that improve performance HP MPH & tq. Could it prodce a lean motor. Air box is stock I woould like to change it to a K&N. If I do that will it create a lean motor or are both these mods pretty much bolt on and go. With the added prop size for the increased RPM's which should be about 200 to 400. Am I correct in making that assumtion on the RPM rule of thumb say for every 200 RPM 1 prop size up?????? or down??? to be in the correct RPM range for the motor.

    just dont want to buy something and then learn about the right stuff after I own it $$$$$$$$$$$

    Mark
    Last edited by Mrs.HLB; 04-07-2010 at 03:31 PM.

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    Senior Member blurred vision's Avatar
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    Had a 21 daytona with the exact same setup....ran 5100 rpm with a 24 prop,at 77 MPH....26 seems a little steep for that boat....good luck

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    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by blurred vision View Post
    Had a 21 daytona with the exact same setup....ran 5100 rpm with a 24 prop,at 77 MPH....26 seems a little steep for that boat....good luck
    thank man you are the first too comment on this in three days thanks again

    HLB

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    Senior Member OLD MAN ON THE LAKE's Avatar
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    The 22 might be the best prop for skiing.You want a prop that will get the boat on plane fast and will also be easy on the drive.The 26 is too big for your power even with better exhaust.
    If you want more top end try a 24 Bravo or 25 Mirage three blade.Any good prop dealer should allow you to exchange till you get it right.
    Laveycraft or Teague should be able to steer you in the right direction.
    I have a 25p Mirage as new condition for $200 if you want to go that direction.The Mirage might be the fastest prop but will not be as good in the turns.
    Having a ski prop and a taller higher speed prop is always good IMO.If you ever go to Lake Powell you will want that 22.
    More air into and out of the engine is always a good idea if you want to spend the money.Don't expect much more than a couple mph.If you decide to change the exhaust do it before you start testing props.
    Good luck.
    P.S. use a GPS and your normal load ( passengers,gear,fuel ect.)when testing different props.

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    Floatin dirty Lavey29's Avatar
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    I know years ago I had a 502efi and when I added some exhaust, I had to have the module re-programmed to prevent a lean condition. I would call IMCO and ask them directly, I believe the newer merc motors can accept some exhaust upgrades without any other mods and no lean condition develops. An example of that is the CMI pipes for the 496 which do not require any other mods just bolt on and increase prop pitch. I would say the others provided good advise. Keep the 22 as a ski/ back up prop and try a 24 or 25 for all around performance and top speed.
    Last edited by Lavey29; 04-09-2010 at 12:18 PM.

  8. #6
    Floatin dirty Lavey29's Avatar
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    Quote Originally Posted by blurred vision View Post
    Had a 21 daytona with the exact same setup....ran 5100 rpm with a 24 prop,at 77 MPH....26 seems a little steep for that boat....good luck

    I had the same boat and set up also but think I was running a 25 Hydromotive Q4

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    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by OLD MAN ON THE LAKE View Post
    The 22 might be the best prop for skiing.You want a prop that will get the boat on plane fast and will also be easy on the drive.The 26 is too big for your power even with better exhaust.
    If you want more top end try a 24 Bravo or 25 Mirage three blade.Any good prop dealer should allow you to exchange till you get it right.
    Laveycraft or Teague should be able to steer you in the right direction.
    I have a 25p Mirage as new condition for $200 if you want to go that direction.The Mirage might be the fastest prop but will not be as good in the turns.
    Having a ski prop and a taller higher speed prop is always good IMO.If you ever go to Lake Powell you will want that 22.
    More air into and out of the engine is always a good idea if you want to spend the money.Don't expect much more than a couple mph.If you decide to change the exhaust do it before you start testing props.
    Good luck.
    P.S. use a GPS and your normal load ( passengers,gear,fuel ect.)when testing different props.
    Thanks for the info. I don't know If I put this in ther so if it is a double post sorry current owner was hitting the rev limiter with a 22 at lake tahoe. In March at the river with the 26 he hit 5100 @76mph gps by himself and a half load of fuel. He said that when there is a load inthe boat say 5-6 people and full of fuel it hits 48to 49k. When you do the #'s game with props the only advantage I see with the 24 is it will probably run 49 to 5K loaded and with me in it alone I would probably hit the rev limiter it red lines @ 5150. I still need to lake test this thing one more time if I buy it and I want to go to elsinore for the high speed zone area that will tell all the truths and squash any lies Thanks again

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    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by Lavey29 View Post
    I know years ago I had a 502efi and when I added some exhaust, I had to have the module re-programmed to prevent a lean condition. I would call IMCO and ask them directly, I believe the newer merc motors can accept some exhaust upgrades without any other mods and no lean condition develops. An example of that is the CMI pipes for the 496 which do not require any other mods just bolt on and increase prop pitch. I would say the others provided good advise. Keep the 22 as a ski/ back up prop and try a 24 or 25 for all around performance and top speed.
    Thanks for the info I appreciate it.

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    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by Lavey29 View Post
    I had the same boat and set up also but think I was running a 25 Hydromotive Q4
    Is the 4 in Q4 to identify the prop as a 4 blade ??????????

  12. #10
    Senior Member OLD MAN ON THE LAKE's Avatar
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    Quote Originally Posted by Mrs.HLB View Post
    Thanks for the info. I don't know If I put this in ther so if it is a double post sorry current owner was hitting the rev limiter with a 22 at lake tahoe. In March at the river with the 26 he hit 5100 @76mph gps by himself and a half load of fuel. He said that when there is a load inthe boat say 5-6 people and full of fuel it hits 48to 49k. When you do the #'s game with props the only advantage I see with the 24 is it will probably run 49 to 5K loaded and with me in it alone I would probably hit the rev limiter it red lines @ 5150. I still need to lake test this thing one more time if I buy it and I want to go to elsinore for the high speed zone area that will tell all the truths and squash any lies Thanks again

    I have been wrong many times but something is not right here.A stock 454 mag turning a 26p bravo at 5100 in a 21 foot vee bottom ?

    BOB TEAGUE to the white paging phone,we need you to retest a boat.

  13. #11
    Floatin dirty Lavey29's Avatar
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    Quote Originally Posted by Mrs.HLB View Post
    Is the 4 in Q4 to identify the prop as a 4 blade ??????????
    Yes, Hydromotive makes good all around 4,5 and even 6 blade props. Mercs are good also of course but when I had my smaller boats, the hydromotives all seemed to work a little better for me. You can keep your 26 prop and just have it tweaked a little to your specifications. Such as taking the diameter down slightly to pick up 100-200rpm or change the cup size slightly or even change the pitch down to a 25 if you want. I had a Maximus 15 5/8 x 30" that was to big for my boat and had it modified to 15 x 29" for my application. Bronson Hill props in Santa Ana can do the mods for you.

  14. #12
    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by Lavey29 View Post
    Yes, Hydromotive makes good all around 4,5 and even 6 blade props. Mercs are good also of course but when I had my smaller boats, the hydromotives all seemed to work a little better for me. You can keep your 26 prop and just have it tweaked a little to your specifications. Such as taking the diameter down slightly to pick up 100-200rpm or change the cup size slightly or even change the pitch down to a 25 if you want. I had a Maximus 15 5/8 x 30" that was to big for my boat and had it modified to 15 x 29" for my application. Bronson Hill props in Santa Ana can do the mods for you.
    Thanks so much that hit the nail on the head

  15. #13
    Senior Member Mrs.HLB's Avatar
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    Quote Originally Posted by OLD MAN ON THE LAKE View Post
    I have been wrong many times but something is not right here.A stock 454 mag turning a 26p bravo at 5100 in a 21 foot vee bottom ?

    BOB TEAGUE to the white paging phone,we need you to retest a boat.
    Like the post says I could not get a WOT on the test because of the lake patrol 35MPH tops. I am getting better with understaanding this prop thing though. Just have to test at elsinore I guess one and done so to speak

    Thanks for all your help

    Mark
    MR HLB

  16. #14
    Floatin dirty Lavey29's Avatar
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    Well if you are in Corona, you are a short ways to Elsinore. They have a no speed limit lane down the center of the lake with bouys marking it and you can go as fast as you want there.

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