Alpha vs. Bravo drag and HP loss?

Discussion in 'Sterndrives' started by Red Tide, Sep 13, 2009.

  1. Red Tide
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    Red Tide Junior Member

    If you have two 23' identical boats with 300 hp V8 engine 55-65 mph speed range, one with an Alpha Gen II outdrive and one with a Bravo 1 outdrive, which will go faster? I've been told that the Bravo will hold up better over time, but that the alpha has less drag and will be ~2 mph faster? True?

    Any first hand experiences with a side-by-side comparisons?
     
  2. marshmat
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    marshmat Senior Member

    In theory, the Alpha could be very slightly faster than a standard Bravo 1, by virtue of its smaller, lower-drag gearcase. Depends on the prop and gear ratio as well, of course.

    In practice, 300 hp at 65 mph is right at the limit of what an Alpha can handle. It'll still have a warranty at this rating, but it probably won't hold up as well as a beefier drive like a Bravo or any of the Volvos.
     
  3. Red Tide
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    Red Tide Junior Member

    Is there a good head-to-head comparison of a bravo 1 vs. volvo sx drive somewhere?
     
  4. Hundredcaliber
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    Hundredcaliber Junior Member

    What about the Alpha one, how will it hold up.
     
  5. Red Tide
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    Red Tide Junior Member

    I believe Matt - not as well as a Bravo - some talk of changing the oil in their alpha drives every 15 hours as it only holds a quart and a half. But you can have three alphas for the cost of a bravo, or more uppers if that's what lets go, and still come out ahead if money is tight or use is low.
     
  6. Red Tide
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    Red Tide Junior Member

    Sorry Hundred, I think you meant how does the Alpha Gen I compare to the Alpha Gen II in strength/durability/problems. Good question. I don't know the answer.
     
  7. Hundredcaliber
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    Hundredcaliber Junior Member

    That's exactly what I meant. I'm in the building stage of putting together a Ford 351 to a Alpha I drive. The price on the SEI 106 looks appealing to me. I would like to hear if the service going to be there with the Alpha I?
     
  8. marshmat
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    marshmat Senior Member

    I don't know how the first- and second-generation Alphas compare, reliability-wise.

    You say you're using a Ford 351 (Windsor?) for this? 300ish horses and 350-400 ft.lb is an awful lot to ram through an Alpha, whatever generation you choose. It's a low end, mass market drive intended for something with a 200 hp V6 that lives on a trailer and goes out for six hours each weekend. If you're going to push your drive hard, perhaps a Volvo or one of the Merc Bravos would be a better choice. There are also many surface drive options that, while rare, can work very well and are cheaper/simpler.
     
  9. powerabout
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    powerabout Senior Member

    Merc sold 351W as a 233 with a twin barrel carb.
    With a 4 barrel it was a 255 but that was only packaged on a II drive.
    as a marine engine it would be lucky to have much over 300ftlbs if that.
    If your building your own spec engine then ??
    The weight of the boat is the key to the drive lasting
    If it will do 40mph it wont live that long
    If it will be doing 60 it will live.
     
  10. Hundredcaliber
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    Hundredcaliber Junior Member

    Greetings to all... The boat had a OMC with a Chevy 283 when I got it. From what I'm hearing is that you cant get the Bravos or the newer drives to hook up to the older style engines. I was told the Alpha1 was the only option.
     
  11. CDK
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    CDK retired engineer

    The Alpha-1 1th generation cannot cope with 300 (Merc) HP. In my drive the vertical shaft snapped in the first week. I must admit that the drive was already used approx 50 hours with a 250HP engine.
    As far as I know the difference between 1th and 2nd gen. is minimal. Some extra holes for lube monitor and speed pickup, simple bolts and nuts to fasten the lower housing instead of recessed bolts and better looking trim cylinders.
    And of course different way to attach the upper bellows. I think it's just cheaper to manufacture, not better.
     

  12. powerabout
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    powerabout Senior Member

    CDK
    Yep, the big jump in strength was from the old 1 drive to the Alpha.
    The old box had the gears cut such that they pulled together like an old outboard and also had the preload button on the driveshaft.
    The alpha cut the gears the other way and had hence have the tapered roller the other way on the driveshaft and no need for the button on top. ( like OMC)
    Removing the button also strenghtend the drive shaft as the hole went down past the oring groove, without the hole that shaft was stronger in the oring groove area which was one weak link.
    The drive shaft was alot beefier in the area in the lower unit as the tapered roller is now installed from the top allowing the shaft to be larger better supporting the drive shaft pinion bearing
    They also started using near net forged gears which are much stronger
    I installed the very first Alpha in Australia as a spare part to a 260 MCM that broke under w/tee as the drive unit was installed in a boat too heavy for it ( all engine problms are caused by boat builders)
    Dont forget Merc also sold 330HP ( 454 chev) Alpha....it worked on light boats???
    I supplied a drive to a ski racing boat with about 500hp small block and used the short shaft alpha 1 SS drive. Never broke one but it had helicopter style maintanence...
     
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