Page 3 of 7 FirstFirst 1234567 LastLast
Results 21 to 30 of 61

Thread: omc 70/75 Differances???

  1. #21
    Team Member sheuninck's Avatar
    Join Date
    Jun 2006
    Location
    Orion, MI
    Posts
    136
    Post Thanks / Like

    Default bore, get pistons, the hone to match

    Fred,
    I really appreciate all your "best in class" advice.
    There are no scores in the walls but, being a 30+ year ole block, it may have developed a very snake-ily stroke. I am not sure if I need +.020 or +.030, so they want to:
    bore, get pistons, then hone to match.
    Does this sound right?
    Or, what is the clearance needed for stock pistons?
    Maybe .008" is too much to hone

  2. #22
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    2,086
    Post Thanks / Like

    Default

    the books out in the barn, thinkin it's .004 on the stockers, i'd give them .005 my self,

    check the bore, see what over size you need, then get pistons, then bore, hone
    and chamfur.

  3. #23
    Team Member
    Join Date
    Dec 2004
    Location
    Kingsville Mo
    Posts
    486
    Post Thanks / Like

    Default best 49!!

    What is the best 49 to start with yr./mdl for a se/fe motor?
    Richard

  4. #24
    Team Member Sam La Banco's Avatar
    Join Date
    Aug 2006
    Location
    Northbrook Il.
    Posts
    88
    Post Thanks / Like

    Default

    Set it up for .0035-.004 for the best acceleration, run 24:1.
    After .006 they still go fast, but just don't punch,

  5. #25
    Team Member Smokin' Joe's Avatar
    Join Date
    Mar 2007
    Location
    Texas and Tirol
    Posts
    657
    Post Thanks / Like

    Default Differences

    No, the 70 was simply a choked down 75.



    Quote Originally Posted by yeeeha View Post
    If I remember correctly the 70 hp was 56 cubic inches and the 75 was 49.9 cubic inches. Also, I always liked the 1975 model 75 best.

  6. #26
    Team Member Smokin' Joe's Avatar
    Join Date
    Mar 2007
    Location
    Texas and Tirol
    Posts
    657
    Post Thanks / Like

    Default Differences

    Best skirt clearance is about .025", must file down oversize rings to get ideal ring gap of about .009". Loss of compression with stock ring gap, stuck piston with less than .008".


    Quote Originally Posted by sheuninck View Post
    Fred,
    I really appreciate all your "best in class" advice.
    There are no scores in the walls but, being a 30+ year ole block, it may have developed a very snake-ily stroke. I am not sure if I need +.020 or +.030, so they want to:
    bore, get pistons, then hone to match.
    Does this sound right?
    Or, what is the clearance needed for stock pistons?
    Maybe .008" is too much to hone

  7. #27
    Team Member
    Join Date
    Jun 2005
    Posts
    46
    Post Thanks / Like

    Default Differences

    After the 56 cube was introduced in mid 1980s, OMC kept making the 15" 49 cube as a 75hp to support the race classes. So those years, there were 56 cube 70hp while there was also a 75hp 49 as well as I think a 60 or 65hp 49.

    What they did was keep the crankshaft rating for the 15" 49 cube while the others were propshaft.

  8. #28
    YARD BIRD
    Join Date
    Mar 2006
    Location
    Napa, California
    Posts
    672
    Post Thanks / Like

    Default 75 Short shafts (1975)

    Quote Originally Posted by Barry Strawn View Post
    After the 56 cube was introduced in mid 1980s, OMC kept making the 15" 49 cube as a 75hp to support the race classes. So those years, there were 56 cube 70hp while there was also a 75hp 49 as well as I think a 60 or 65hp 49.

    What they did was keep the crankshaft rating for the 15" 49 cube while the others were propshaft.
    .................................................. ..................................................
    Ihave been told , way back in 1975 , that all the 1975 model 75 horse test power heads pulled over 80 horses on the factory dyno . back in 74 or 1975.Tom Ireland told me on the phone, back in about 1986(?)that the hot set up ,for a sport E then, was an Original (with light weight pistons and the early ,light rods ) and the 1984 or later carbs and exhaust system. the light weight pistons have not been available for a long time ............and the light weight rods and pistons were only legal in the early engines that they came in .
    Last edited by Roy Hodges; 07-30-2008 at 07:45 AM. Reason: more facts

  9. #29
    Team Member Smokin' Joe's Avatar
    Join Date
    Mar 2007
    Location
    Texas and Tirol
    Posts
    657
    Post Thanks / Like

    Default Differences

    The newer carburetors slowed down my 1975 model. I doubt that any 75 was faster on a V-bottom, but later model 75's with heavier pistons and rods, and larger skeg, were equally fast on a tunnel (even if 100-300 RPM slower on the V-bottom). Tom Ireland and bob Schroer at Evinrude Service (sp?) were good guys to have on your side.

  10. #30
    YARD BIRD
    Join Date
    Mar 2006
    Location
    Napa, California
    Posts
    672
    Post Thanks / Like

    Default 75 horse johnny rudes

    Quote Originally Posted by Smokin' Joe View Post
    The newer carburetors slowed down my 1975 model. I doubt that any 75 was faster on a V-bottom, but later model 75's with heavier pistons and rods, and larger skeg, were equally fast on a tunnel (even if 100-300 RPM slower on the V-bottom). Tom Ireland and bob Schroer at Evinrude Service (sp?) were good guys to have on your side.
    .................................................. ..............................................
    .................................................. .................................................. ...............................
    you probably knew that the "hot setup on 1975 - 75horse " was to advance the timing to 19 degrees (instead of the stock 16 degrees , and go one step leaner jet(mainjet). BUT !
    IF your motor don't turn at least 6000 rpm, you have engine trouble. If it is to be competitive , it needs to be able to turn 7000 .Paul Bender went through several powerheads (supplied from OMC , through Tom , experimenting , untill they got this combination . (in sport E class)...... Oh, by the way.... i remember Tom Ireland telling me ,on the phone ..." if you change carbs, you have to ALSO change the exhaust parts , they are a matched set .
    Last edited by Roy Hodges; 07-30-2008 at 12:27 PM. Reason: more info

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. A Howard Pipkorn Class???
    By Ron Hill in forum Tunnel Outboards and Tri Hulls
    Replies: 10
    Last Post: 01-12-2007, 10:15 AM

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
  •