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Thread: New outdrive

  1. #1
    Senior Member skunked's Avatar
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    New outdrive

    My outdrive needs serious attention and my son in law works with a retired boat mechanic who has a freshly rebuilt outdrive that someone didn't pay for.
    It is a 1:70 gear and mine is 1:50. He says it will work fine behind my 260hp. I'm a little skeptical. What do you all think? Both are pre Alphas and he suggests a larger prop. My prop is 14 1/2 x 16p 4 blade.
    I don't want to pull skiers with my 21 footer.
    1978 Glasply 21ft 5.7l Mercruiser R drive "Sandi's Surprise"
    1981 Glasply 17ft 70hp Johnson & 9.8hp Nissan kicker "Skunked"

  2. #2
    Senior Member gordo's Avatar
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    if you switch to the 1:70 you wont know about your prop 'til then. I have always been under the belief that you want the largest diameter regardless. Then chase the pitch that's required to achieve the WOT your boat will need. Your 260 will be around 4400-4600 RPM. My outdrive I just removed is a 1:50 and I squeezed a 16 dia. on and it has been the best setup for my 23 that I've had (it had a 16 pitch too)

  3. #3
    Quote Originally Posted by skunked View Post
    It is a 1:70 gear and mine is 1:50. He says it will work fine behind my 260hp. I'm a little skeptical. What do you all think? My prop is 14 1/2 x 16p 4 blade.
    One way to look at it is running a 1.70 ratio verses the 1.50 is like running a lower axle ratio in a pick up truck. The engine will work less with your existing prop then it did previously BUT turn more RPM's for a given speed. As Gordo said, 4400-4600 should be your WOT goal. I suspect you'll pick up about 300-400 RPM's changing to a lower ratio. If the price is right and you consider that you may need to buy another prop it may be a great buy.
    "Joint Venture" 1978 28' twin 2017 Vortec roller cam 383/6.3L 350hp engines - You name it, I've either replaced it, restored it, rebuilt it or repaired it. That's my job now that I'm retired.

  4. #4
    Quote Originally Posted by gordo View Post
    if you switch to the 1:70 you wont know about your prop 'til then. I have always been under the belief that you want the largest diameter regardless. Then chase the pitch that's required to achieve the WOT your boat will need. Your 260 will be around 4400-4600 RPM. My outdrive I just removed is a 1:50 and I squeezed a 16 dia. on and it has been the best setup for my 23 that I've had (it had a 16 pitch too)
    What prop were you running? I am under the impression the bigger diameter the better as well. I am not sure what prop we have... in the trailer and 6 feet of snow, not quite ready.... soon.

  5. #5
    Senior Member skunked's Avatar
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    Thanks for the replies. I'm thinking of going to a 17 or 18 inch pitch and stay with 14 1/2 inch dia. He wants $550 for it so it's a great deal.
    My current prop is a 4 blade. I'm not interested in hole shot, just cruising the sound. Also I will be adding trim tabs to help with list while running and planing.
    1978 Glasply 21ft 5.7l Mercruiser R drive "Sandi's Surprise"
    1981 Glasply 17ft 70hp Johnson & 9.8hp Nissan kicker "Skunked"

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