Thread: Fast Fred's OMC Mod 50 secrets Thread #2

  1. #671
    Sam Cullis Mark75H's Avatar
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    Looking forward to more once you are certain of the set up
    Since 1925, about 150 different racing outboards have been made.


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    Default Video link #2

    http://www.youtube.com/watch?v=B5TYP-oEpnA

    Here's more testing with more aggressive throttle. Enjoy!

    Tim

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    Default Continued turbo testing

    Ran the turbo again yesterday with a .089" (richer) main jet. Still uninstrumented except for boost and EGT, but seems to run even stronger. Had good water for only 10 min, but saw 11-1/2 psi boost toward top on one run. EGT was 650 at cruise (no boost), then settled at about 750 at full boost - very good. Still won't idle even with a .014" jet. Will install 0.000" air bleeds for the next trial. Also, still blows oil from the reservoir vent - will address this before Hillsdale.

    SLT racer Jeff Howie and friend Dan Hoffman observed (both have driven the boat before). From about 60 mph cruise, dropping the hammer in front of them, that say the boat leapt vertically about 4-5 inches from the water and virtually exploded away in a fit of acceleration. On the one decent high speed pass they saw nothing but propeller in the water - no fin - with the boat horizontal, competely airborn still acclerating. They say the engine is most quiet on boost, cackles heartily off boost(???).

    Once home, saw richer plug & piston reads (nice) and good compression (same 135 psi as before), but possible reed chunks through #2. There are two slight marks in the top of #2 that I don't remember from before - not from metal. Will pull the manifold to inspect reeds and replace if needed. There are no reed stops instaleld: If there's evidence of top side impact damage, they will be re-installed.

    The next run will be Sep 9 at Hillsdale where video will be shot with a head-to-head acceleration contest against Jim Robb's Mean Red VII and Kestrel copy. Also this fall, Dixon Smith has agreed to a side-by-side run from 50 (or so) with his 2.5L Merc powered drag hydro. Both trials should be very interesting!

    Tim

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    Default We have a winner!

    Quote Originally Posted by Mark75H View Post
    I bet this doesn't go .... "eeeeeeee-oooonnnnNNNNN" when the prop catches and it gets on plane .... just "EEEEEEEEEE"

    We will want video of that!


    I predict that the turbo will spool completely up while the prop is slipping and the motor will be at full torque that the prop applies 100% when it catches
    Sam's prediction is absolutely correct: Full boost is achieved by the time the prop grabs - gotta be very careful getting on plane.

    Does anybody know the is the torque limit for the OMC 1/2" driveshaft/coupler?

    Tim

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    Team Member TBuck2003's Avatar
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    Wow awesome Tim congrats on your stick to it attitude... I want to see that thing run. All the best.

    Todd

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    I would like to add to the cautionary notes: when German S5 racer Karl-Heinz Nickel turbocharged his 3.5 ltr BMW and Volvo offshore outdrive (in a 16ft Cormorant catamaran),upon the first try the boost came in with a bang. Amazingly, the lu stayed together, but the prop with the backend of the propshaft went AWOL. This was caused by mismatching the turbo characteristics to the engine demands and cured relatively easily.
    In that context, a 1/2" shaft "feels" awfully thin for some 150 ponies and a steep torque curve.
    Tim, I will respond to your PM from my homecomputer. Company server`s spam filter does not let my response out. rgds.

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    Default Progress!

    Spent a little time in the shop tonight on Virgo. Here's what transpired:

    1) Removed plenum cover to find a pool of 2-stroke oil in the bottom (expected), but no evidence of debris - yea! A small bleed will be added to connect to the factory manifold drain system. Prime adapters will be improved as well - possibly before Hillsdale.

    2) Carefully opened all reeds except for bottom #1 (can't get to them because of the angle) with a slender wooden dowel. There is no evidence of any chipped or broken reeds anywhere. Side note: Never having looked before, I was shocked to find reed travel within 1/16" of internal structure and rods!!! There is no reason for a powerhead tear down. Will reassemble for continued testing.

    3) Disassembled the carb to analyze passages. At least part of the problem has been identified: The mid-range (transition) bleed passes horizontally straight through the carb flange (lower starboard side) and dead heads against the Virgo carb adapter - Duh!. The factory manifold must have a passage drilled directly through the flange into the manifold upsteam of the reeds. Needless to say, the Virgo carb adapter will be removed and drilled to match. This will add transition fuel that is currently blocked.

    Once these changes have been made, some hose test time is in order. This may happen soon as Saturday afternoon. If idle is achieved and/or low end throttle response is improved, another lake test might happen yet this weekend. I'm starting to believe this monster might be tamed yet this summer!

    BTW: All, thanks for your thoughts regarding the 1/2" drive coupler. The 45SS is the beefiest/lightest gearcase available in this size range. My guess is it will survive the 5-10 hours this engine may accumulate in it's life.

    Tim

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    Default Mouth of the beast

    The idle mystery has been solved. Indeed the idle bleed was inadvertantly blocked off (by me). This series of carb uses a slot in the carb flange gasket for feed - have never seen this design feature before now. The engine will be hose tested in the driveway sometime this weekend - it should be much happier. During the re-assembly, this image was shot of the hungry end. Thought some of you might enjoy this.

    Tim
    Attached Images Attached Images  

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    Team JDS Jeff Akers's Avatar
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    Any updates Tim?
    Jeff 93-C



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    Default Turbo updates

    Hi Jeff,

    Thanks for asking. Yes, there's been progress:

    1) The idle problem has been solved.
    2) The front end was removed and reeds inspected - all perfect.
    3) Reed stops will be installed as precautionary measure/to improve life.
    4) Inter-plenum velocity stacks will be installed to smooth mixture flow.
    5) A top entry port will be added to the oil reservoir for turbo oil bypass return.
    6) A top loop 1/2" dia oil vent hose will be installed to free up reservoir pressure changes.

    All this should be done in time for a Labor Day test run. Adjustments will then be made in preparation for an afternoon's testing Friday Sep 9 at IOA Hillsdale. The plan is to run the boat next to Jimmy Robb and/or Rich Welch on the race course and video the event to be posted on YouTube for all to enjoy. Steady as she goes........

    Tim

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