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Thread: 1986 Donzi Z25 Questions?

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    1986 Donzi Z25 Questions?

    Hi,
    New to this great forum and looking for some opinions for a 1986 Donzi Z25 we just picked up. It is originally equipped with a single 454/TRS combo that needs total rebuilding to be ship shape again.

    We have a few questions for you experienced Donzi owners.

    How fast did this boat go back in the day?

    Is it possible to use a small block Chevy instead of the big block or does it need the torque of a 454 engine?

    Would it be possible to run top speeds of 60-65 mph with a 350/370hp or higher small block engine and a more modern outdrive unit?

    Also, would the fuel consumption and range be greater with a small vs. big block engine?

    Your experience and advice would be greatly appreciated.
    Thank you all very much!

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    PM Donzigo about the Z25s he knows them very well. He had a 25 for 8 years and now has a Z33.

    Bob
    Member - WAFNC
    1997 22 Classic (sold)
    1997 Formula 271 Fastech
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    Thanks Bob!

    Jeff

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    Not a bad boat. However not very fast by todays standards, but respectable none the less. They just were not speed demons, it also was probably only the 330 version big block that was in there. Especially if it is equipped with an Alpha as it is a 1986 model..

    I will caution you if it is an alpha that boat and power is a lot to put an alpha thru. It is the wink leak and should be upgraded to a bravo for optimal longevity.. If it is a TRS, then not so much of a worry as it is a durable unit, however I would have it gone thru and make sure it has been serviced well. If it is a trs and in rough shape then still a bravo conversion may also make sense..

    Anyway, on to your other questions....

    Torque is going to be important, a small block would fit in there and work if it was high output, but it will have to work harder in that application because of the size and weight of that boat. IMO you would be best putting in a healthy big block as it would not have to work as hard and would be able to give you better speed and fuel economy in this scenario..

    Actually I did a Z21 over for one of my clients recently & re-powered it. It originally had a 330 hp big block merc in it. I re-powered it with a new custom 450hp big block. He picked up some speed and his fuel economy is much better. The boat can cruise easier and use less fuel when doing it now..

    Hope this helps.. Jamie / Lakeside Restorations

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    Thanks for the tips.

    Been looking into the 383 small blocks because of the weight reduction/RPM and HP figures, but maybe a new 454 might be an easier way to go.

    Anybody out there run a boat of this size with a warmed over 383 stroker small block?

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    As I mentioned to you on Friday night when you called me, Nothing against the 383. It is a great engine and works very nicely in many smaller applications. However IMO the BBC will work better for this application for the reasons I already discussed with you the other night.

    But as with anything I guess, usually one needs to do what makes them most happy and fits their budget the best..

    Jamie / Lakeside

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    Thanks Jamie, was just putting it out there just in case someone might have tried it. I was searching around and found some info on some new Vortec engines Mercury Marine was offering in Europe.
    It looks like we might go with a 502 base engine, but this is an interesting read.
    http://www.gm.com/vehicles/innovation/powertrain-technology/engines/specialized/marine/REV_3_2011_Marine_Engines.pdf
    Thanks again!

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    Quote Originally Posted by IpanemaSports View Post
    It looks like we might go with a 502 base engine,......
    There is one for sale on the board, right now. I believe it is fully dressed.

    B
    Member - WAFNC
    1997 22 Classic (sold)
    1997 Formula 271 Fastech
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    Thanks, looks like a good deal.

    We're looking to run a 502, Merlin heads & carb set-up.

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    Z25 is pretty close to a 24' black widow hull bottom and weight. I had a 24 widow and so did fishnsucks. Figure a 454 with 365hp is a 60mph boat. Need about 500hp to go 70mph. Assumes the correct diameter size/pitch prop of course. Chevy 454 marine engines seem to be very plentyful so I would go that route. I see a couple late 80's Z25 boats for sale in MN, WI, and OH area from time to time. All freshwater boat histories and an inexpensive way to get into a Donzi. They are well built nice boats. Most are kinda rough shape after all the years however. Nothing that 5-10 grand worth of TLC wont fix however.
    Tuco: When you have to shoot, shoot, don't talk.

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    It took me over 500 hp to break 70 with a trs. It's a fun boat to drive now though.

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    Thinking of switching from the TRS to Bravo drive. Was talking with an old friend and he said that it would be a good idea to keep the engine in the same location and that with a "drive shaft" it would be possible.

    He said it wasn't a "plug & play" conversion, but would be worth it to maintain balance of the hull.

    Have any of you guys done this or know what or who makes the parts needed for this conversion?

    Thanks for the help guys!

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    Here's a pic of her.

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    Change it to the Bravo 1 drives.

    Stay with whatever Lakeside advises and you can't go wrong. Jamie knows his stuff.

    Richard
    .........Boats are proof that God loves us and wants us to be happy!

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    Quote Originally Posted by IpanemaSports View Post
    Thinking of switching from the TRS to Bravo drive. Was talking with an old friend and he said that it would be a good idea to keep the engine in the same location and that with a "drive shaft" it would be possible.

    He said it wasn't a "plug & play" conversion, but would be worth it to maintain balance of the hull.

    Have any of you guys done this or know what or who makes the parts needed for this conversion?

    Thanks for the help guys!
    Dont worry about the shifting back of the engine to mate to the B1. If you are going to do it, just plug the transom & run a conventional B1 style set up if you are not staying with the TRS. Going to a B1 with a jack shaft application or plug in model will only greatly add un needed expense and grief for this boat. Usage of a jack shaft is primarily done in boats with staggered twin or triple engines. No need to re-invent the wheel here..

    The TRS BTW is not a bad drive, and if in it and it's tranny are in good shape they can hold reasonable power, it is just getting tougher to get some of the parts for them, and some parts are just NLA..

    FWIW, In regard to switching to a B1 set up from TRS. It is not that the B1 stuff is always more reliable or tougher. It is just usually easier to get parts and service for them since the TRS line up was dropped years ago.. Other than that the Bravo is just a little shorter than the TRS which usually also allows a little less drag & potential for speed increase on some hulls..

    Jamie / Lakeside

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