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

  1. #221
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    1,389
    Post Thanks / Like

    Default

    i talked to a Dude that worked at OMC, he built Mod 50's for them. he said that thay took a 56 case put 2bbls on it with big reed blocks, and did the exhaust like i was thinkin, it only would make 102hp. i've heard tails of 110-115hp but can't say for sure. the said the carbs did not help it, or the exhaust. said the 56er did best with 1bbls and stock exhaust.

    i'll let yas know how the 56er does side by side with a 19s

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  2. #222
    Team Member
    Join Date
    Nov 2008
    Location
    Horseshoe Bend, ID
    Posts
    657
    Post Thanks / Like

    Default Fuel system concern

    Hi Fred,

    Take a look at the attached schematic and you might consider doing a little more plumbing work. The engine looks like fun tiller style!

    Tim
    Attached Images Attached Images  

  3. #223
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    1,389
    Post Thanks / Like

    Default

    the Mallory regulator wanted it set up like i have it, it has a Big needle in it,
    the Loop is from the pump to the reg' then back to the tank. the pump never backs up, it's always free flowin, the needle adjustment forces fuel and psi to the fuel rail so there is about 80gals an hr available to the carbs if they want it,
    but the pressure never changes.

    any chance you could make the schematic bigger? i have a gauge at the top of the fuel rail to recheck the psi.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  4. #224
    Team Member
    Join Date
    Sep 2008
    Location
    Singapore/Melbourne/Italy
    Posts
    780
    Post Thanks / Like

    Default

    Fred
    with that set up the regulator is contolling flow as well pressure.
    If the reg is on the return side of your fuel rail it only controls the pressure.
    Ya just need to be sure the reg can flow all the fuel at the regulated pressure, that you need.

    If your fuel rail is a dead end then the only escape of any air in the fuel is through he carbs.
    ( I knows thats how OMC say to do it because they cannot tell you to have a return line as its against USCG regs)

    Changing it around may not fix anything BUT it sure will eliminate a couple of potential problems.

    Cheers
    Powerabout

  5. #225
    Team Member
    Join Date
    Nov 2008
    Location
    Horseshoe Bend, ID
    Posts
    657
    Post Thanks / Like

    Default Schematic

    Indeed, the benefits of the loop bypass system are elimination of air bubbles, constant flow/pressure through the fuel rail, and tremendous thermodynamic benefits should you employ the cool can. Yep, it's a bit complicated, but my experience is it absolutely eliminates burnt/detonated pistons due to fuel starvation. Thus the only fueling error becomes improper jetting. You know the saying: Too lean, too long, too bad! Will make a better schematic and post sometime later.

    Tim

  6. #226
    Sam Cullis Mark75H's Avatar
    Join Date
    Nov 2004
    Location
    Annapolis, MD USA
    Posts
    1,795
    Post Thanks / Like

    Default Ice is nice

    Thanks for the diagram, Tim.

    I have been considering a cool can for 850, but could not figure out how to really get enough BTU's removed from the bowls and lines without a lot of bulky insulation.

    This set up would also allow pre-cooling the whole tank of fuel ... you have probably made me a very busy boy.
    Since 1925, about 150 different racing outboards have been made.


  7. #227
    Team Member
    Join Date
    Nov 2008
    Location
    Horseshoe Bend, ID
    Posts
    657
    Post Thanks / Like

    Default Cold fuel

    Now you're cooking with ice cold Avgas........ Gotta love the latent heat of evaporation!

  8. #228
    Sam Cullis Mark75H's Avatar
    Join Date
    Nov 2004
    Location
    Annapolis, MD USA
    Posts
    1,795
    Post Thanks / Like

    Default

    Quote Originally Posted by Tim Kurcz View Post
    Now you're cooking with ice cold Avgas........ Gotta love the latent heat of evaporation!
    I'm an AC/Refrigeration mechanic ... I use latent heat of evaporation every day, this is actually about "sensible" heat. The latent heat of evaporation is unchanged.

    Do you know the correct fuel height in a KA bowl for overflow set up? I'll probably be putting a stand pipe in from the bottom.
    Since 1925, about 150 different racing outboards have been made.


  9. #229
    Team Member proprider01us's Avatar
    Join Date
    Apr 2005
    Location
    indianapolis indiana
    Posts
    46
    Post Thanks / Like

    Default 750 motor

    Hey Tim, if running this system on a 750 merc., what psi do you recommend for a set of KC carbs. Can I assume you keep the fuel tank vented? Thanks for all the insight.
    Joe
    Likes boatbuilder41 liked this post

  10. #230
    Team Member
    Join Date
    Nov 2008
    Location
    Horseshoe Bend, ID
    Posts
    657
    Post Thanks / Like

    Default More carb stuff

    For KA's and KC's, I've never actually measured float height compared to fuel height - Bud explained that except for alky applications there was no need to free-flow Tillotsons. It stands to reason that you prime a KA or KC to inlet valve shut-off, then remove the top and float, that you should be pretty close. If you're too high it will eventually overflow the standpipe in rough water. Best idea is to make the pipes adjustable - or find an alky guy that has experience with them.

    As for fuel pressure, conventional (floated) Tillotons always run well at 2-1/2 PSI. I've never run a return system because twin pumps feeding to center always get the job done.

    According to Bud, stand pipe carbs always run lower pressures - the objective is to keep the bowl at a constant level regardless of RPM. Flow/bypass is more important than pressure. Again, you need to find an alky guy willing to share the knowledge.

Thread Information

Users Browsing this Thread

There are currently 5 users browsing this thread. (0 members and 5 guests)

Similar Threads

  1. An Amazing Story: Cover Thread
    By Mark75H in forum Outboard Racing History
    Replies: 0
    Last Post: 10-13-2008, 05:48 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •