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Thread: 496HO to 502

  1. #1
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    496HO to 502

    I've hesitated posting my engine swap because I didn't want to jinx it. I don't actually have the engine yet, but I have negotiated a price and we have an agreement (but no $ has changed hands yet). Carl was kind enough to check the motor out for me. The seller just needs to change a couple things and then it's going to the dyno. If all goes well...which I suspect it will, it should ship out in a couple weeks.

    The other reason I hesitated posting was I work a lot slower and don't do nearly as good work as others here, so I might just embarass myself. Then I figured......what the hell......I've embarassed myself plenty of times, once more surely can't hurt.


    Anyways, for those that don't know, I cooked my Procharged 496HO last year. Wasn't the S/C or engine's fault. I loved that motor. It ran great. It was my stupidity that killed it. Originally I planned to rebuild it, but a parts (delivery) mix up caused me to miss the end of the season, so I changed course and decided to put in a 502
    After not finding what I want, Fogducker called me because he located an ultra low hour 496 near me. Took a look and purchased it. It was missing a few parts, but I could combine the 2 motors and be back on the water for cheap. Well, because I work soooo slow, it sat for a couple months and recently a previous contact called me about his 502. One thing lead to another......and now I'm back to a 502. Procharged of course!

    Summers fast approaching and besides the motor swap, I still need to do some glass work and install my new tabs. I also figured while I'm at it I'll relocate the steering rams to line up better with the Blackhawk. Not too big a deal for a lot of folks here, but free time is hard to come by for me.
    Why is faster never fast enough.

  2. #2
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    A few pics of the start.

    Stripped most everything off the transom. Figured while I was at it, I'd relocate the steering rams to line up better with the Blackhawk. I also removed the Donzi logos off the side. I plan on putting the S/S Donzi letters on. I plan on adding a couple more layers of glass in the bilge as well as on the transom for the new trim tabs.

    In the bilge pic, you can see the "stiffeners" that were installed as part of Donzi's warranty repair schedule. Ever since I had the repair done, I would always take on some water. Well, when I took off the transom assembly, I found out why. Turns out the shop that did the repair didn't install the transom assembly gasket or use any sealant.

    I included a pic of the transum thickness for those that are interested. The transom is the same thickness all the way across.


    On a side note, I have never been able to find a conclusive aticle on when Merc stopped using forged cranks in the 496 Mag/HO. Most posts I find state forged cranks were only used in 01's and possibly 02's. I did find one post where a guy stated they changed to cast in 04. My engine seems to support him. The crank in my 496HO is forged and although the boat is an 04, the motor easily could have been built in 03.
    Mute point for me now though......as I toasted the crank. Seems forged doesn't do much better than cast without oil.
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    Why is faster never fast enough.

  3. #3
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    This is the original dyno sheet from the 502 I have coming. This was done with the motor running a MEFI 1 and boost referenced fuel system. The seller is tossing the boost referenced system and installing a MEFI 3 with a proper boost map. I suspect it should be able to be tuned to squeak a few more ponies out of it.

    Dyno.JPG

    On a dyno, I've never understood the difference between the HP/TQ vs Corrected HP/TQ. Can anyone enlighten me?
    Why is faster never fast enough.

  4. #4
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    Is the X going up while it's all apart for the proper X of the Blackhawk?
    I wouldn't think it'd be much more work with all your doing.
    2006 CLASSIC 18 WHIPPLED MX 6.2, BRAVO 1, STAINLESS MARINE EXHAUST, LATHAM STEERING, IMCO 2" SHORTY, LABBED MIRAGE PLUS

    TALK IS CHEAP, I'M FROM THE "SHOW ME STATE" SHOW ME

  5. #5
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    Great photos, great thread, all looks cool, keep us informed, good luck.
    Cheers,
    Pismo
    1996 22 Classic
    Red with Stainless Windshield
    Stock Gen VI 502 Magnum MPI-415hp
    Stock Bravo I
    25" Mirage Plus
    74.5mph best @ 5050rpm GPS (Speedo said 80)
    27" Labbed Mirage Plus
    75.5mph best @ 4800rpm GPS (Speedo said 82)

  6. #6
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    Yeller,

    What tabs are you switching to? Your steering mount area looks low to me , I can't get to my boat to compare , but i'm pretty sure mine mount above the boot stripe. My reason for mentioning is I took off my bennetts 2 yrs ago and I have had a difficult time finding tabs that would fit in my application. I finally arrived at a set of eddie marine sponson tabs but had to get the rams customised by them to get an effective operating range. I couldn't find a tab with transom plates that would fit around my steering.

    - Marshall
    1978 Magnum Starfire "MAYHEM"
    1994 Donzi 22 Classic 540/Blackhawk - Sold
    1982 Midnight Express 32 SS

  7. #7
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    The steering rams are mounted a little lower than my Ziegers, but only by an inch or so. Mine are roughly centered on the top accent stripe of the boot stripe.
    Don
    '01 22 Classic, 502/B1
    And a bunch of other stuff

    "If everything seems under control, you're just not going fast enough" - Mario Andretti

  8. #8
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    To answer a few questions:

    I will not be raising the X. Although the BH would work much better, I don't want to build the boat around a drive that is out of production and difficult to get parts for. I have no idea how long I'll keep the BH on.

    Steering rams are a low because I wanted to attach the rams to the bottom of the wing plate. Most attach their rams to the top side. Mounting on the bottom side worked fine for the Bravo, but I have no choice but to mount on the top side with the BH. Rams hit the drive and I can't make them fit on the bottom. By moving them up, I can keep the rams level regardless of which drive I use. I wouldn't bother with this exercise, except I'm already doing transom work and a couple more hole repairs is no big deal.

    Tabs are going to be 24" Eddie Marine's. They will fit where I want them, but I do have a problem with the curvature of the transom. With one side of the mounting plate snug against the transom, the other side has close to 1/4" gap. Haven't fully decided how I'm going to solve this problem
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    Why is faster never fast enough.

  9. #9
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    The dyno game...

    I believe the adjusted readings are for ideal temperature, humidity and barometric settings, typically at sea level and 60 degrees.
    The kind of dyno and the operator can have a big impact on what the number looks like, too. Someone more knowledgable than me will step in here, but I have looked at a few of these lately, and it really is a component of your engine builder, too.

    A couple of observations, that is a very flat torque curve and it drops quickly. It would be interesting to see how it comes up from 3000 RPMS to get a bigger picture. Also, it peaks at 4400 and drops six to seven percentage points at the RPM where you will most likely prop it at just less than 4800 rpms. On mine, this torque drop is about 2 points, with a peak at just under 5000 and propped at 5400, as a comparison. I would think you could prop for a little more peak RPMs, if they are there, especially with the 31 BH props. The torque curve on mine drops so gradually that I can spin all they way to 6000, if I want to.

    I would spend the time to have the engine dynoed with the new MEFI, once you get it. Fuel delivery and timing would be my primary concerns. This needs to be done by someone who can tune the MEFI on the motor on the dyno stand. The ship the ECM to a tuner and hope they got it right method might get you there, but I think you know what happens if you don't.

    If you don't have someone there that can do this, it might be worth buying some dyno and tuning time from Brian, here in Detroit, before the motor comes your way. You will know where the thing stands for sure, if he gets his hands on it.

  10. #10
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    i'm having a little problem with that dyno sheet...
    Charter Member - WAFNC, SBBR, KWOSG
    1955 Perfect Mate
    1986 Hornet III, 502-415 TRS

    www.donzi.org


  11. #11
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    RT, thanks for the breakdown. The motor will be getting tuned on dyno with the new MEFI. I'm hoping to get it sent to Crockett.


    Buizilla, that comment is suppose to help me how? You're a wealth of knowledge, but I've never understood why you always have to post in riddles.
    Why is faster never fast enough.

  12. #12
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    LOL

    riddle me this > assuming the C.A.T. stands for charge air temp(?) how the hell did they get it to 39*F and keep it there perfectly? do they own Ready Ice Co.? I don't think you'll be in 39* real world water temp will you?

    and all this was at -.2 what?

    there's a couple more things, but we'll start there, until it's dynoed again..
    Charter Member - WAFNC, SBBR, KWOSG
    1955 Perfect Mate
    1986 Hornet III, 502-415 TRS

    www.donzi.org


  13. #13
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    Thanks Buiz. Now why couldn't you have said that in the first place. I didn't know what 39deg was measuring. Until you posted -.2psi, my brain was thinking vacuum (which of course isn't measured in psi). So...thinking it was vacuum, I assumed it was at negative because it's a boosted motor and the dyno gauge couldn't read it. Yes, seems like a stupid interpretation now, but............ahh.....I have no but........it was stupid.

    RT, missed the part of your post suggesting Brian dyno the motor. Great idea. It was the seller that said he would send it to Crockett, but I'd rather it go to someone that is known to members here.
    Why is faster never fast enough.

  14. #14
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    Fixx...

    I'm local to TC. Way over-rated, way over-priced, and his dyno-sheets, well, you know what I am going to say next...
    Oh, and if he can be bothererd to return a phone at all, Glenn might get in. There are other places in Detroit that can get the job done.

  15. #15
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    Agree with RT

    I am new to this performance boat stuff. Last year I was budgeting a pretty good $ project. I went to see Brian he was right on the money spent time with me. I could not get thru to TC. When I did I advised I had sent an email and they advised they get too many to go thru. He promised to get back to me with quote but I never heard from him. I called once to follow up he didn't call back.. When a project I can follow thru with does come up it will go to Bryan!

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