Thanks Thanks:  0
Likes Likes:  0
Page 3 of 5 FirstFirst 12345 LastLast
Results 21 to 30 of 47

Thread: Mercury 70

  1. #21
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default

    Quote Originally Posted by Fast Fred View Post
    Some NOS wake it up
    Fast Fred,

    While i do indorse the use of N2O, The problem for me with spraying is that now to get full benefit of the N2O would to prop accordingly to ether situation and that cant be done… so I will have a slug when I am not running spray because now the prop is too big… or in the situation of running spray while propped to be not spraying, I will end up out of the power band. Unless the button is always pressed down.

    Good if your running the 1/4... Bad idea if you want the power all the time... especally at $5.25 a pound.

  2. #22
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default

    Quote Originally Posted by jeff55vDSH View Post
    I agree with Sam.
    I think the single biggest problem with the 3cyl Merc service engine is cooling. Be sure to have a good water pump, thermostat (if you use it at all), and have the cooling vent at the top of the block installed.
    What is the HP rating limit on your boat?
    Any hotrodding gains will be small and perhaps barely noticable in a service application.
    I'd look for the biggest engine that is legal for the boat.
    I hot rodded my family ski boat by installing a bigger motor than what it was rated for and then putting engine covers on it from a lower hp motor so it would be "legal" if the coast gaurd stopped me. But, I know I could have been caught if they'd have run the serial numbers. I guess it's hard to recommend that somebody do what I did.

    I like the idea ... thats why that 70 is already on the back of the boat... as it's only rated for a 50
    Attached Images Attached Images  

  3. #23
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default Leaf Blower

    Maybe I will Build an air box and attach to it a leaf blower… something like 4 psi of boost at 900 CFM… boost reference the fuel… and see what happens...

  4. #24
    Sam Cullis Mark75H's Avatar
    Join Date
    Nov 2004
    Location
    Annapolis, MD USA
    Posts
    1,795
    Post Thanks / Like

    Default

    Quote Originally Posted by Roy Hodges View Post
    I have NO need for ANY 6 cylinder motor. I am just asking because of my curiosity. I am always wondering "what if ?'. I knew of one mk 75H motor. Stevens had hopped it up . way back in the 70's . I remember he did NOT like the port timing of the Mk 55h & Mk75H . He did like the Mk 58 port timing .
    Mk58 and fishing Mk75 porting are the same ... also the same is Mk55 fishing porting

    I have one Stevens block, definitely higher porting on the exhaust; might be std fishing porting on the intake
    Since 1925, about 150 different racing outboards have been made.


  5. #25
    Sam Cullis Mark75H's Avatar
    Join Date
    Nov 2004
    Location
    Annapolis, MD USA
    Posts
    1,795
    Post Thanks / Like

    Default Plan D

    Quote Originally Posted by Plan-b View Post
    Maybe I will Build an air box and attach to it a leaf blower… something like 4 psi of boost at 900 CFM… boost reference the fuel… and see what happens...
    48 ci ÷ 12 (to change to cubic feet) = 4 cubic feet;

    times 6,000 rpm

    6,000 X 4 cubic feet = 24,000 CFM ... the Merc will suck the leaf blower in, or at least being connected to the leaf blower will be a major restriction to the Merc

    (if you did boost the motor, the fuel would be automatically boosted by the increased pressure in the crankcase which operates the fuel pump)

    BUT ... supercharging a 2 stroke does not increase cylinder pressure in most instances because unlike a 4 stroke, the transfer (or "cylinder intake") port closes first while the exhaust port is still open - releasing any pressure increase to the exhaust pipe.

    So, even a 60,000 cfm leaf blower won't help beyond some slightly improved intake and cylinder scavenging
    Since 1925, about 150 different racing outboards have been made.


  6. #26
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    1,389
    Post Thanks / Like

    Default

    the leaf blower thinkin will just lean it over. could go to alcohol and splash in some Nitro methane, not like it's guna blow the head off

    doublein the hp with NOS, works but is short lived

  7. #27
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default

    I Know it has no outboad in it ... just kinda fun to watch and think...

    HTML Code:
    http://videos.streetfire.net/video/ab544e3b-5dff-416d-9cfd-a1ad23ca9564.htm

  8. #28
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default

    Quote Originally Posted by Mark75H View Post
    48 ci ÷ 12 (to change to cubic feet) = 4 cubic feet;

    times 6,000 rpm

    6,000 X 4 cubic feet = 24,000 CFM ... the Merc will suck the leaf blower in, or at least being connected to the leaf blower will be a major restriction to the Merc

    (if you did boost the motor, the fuel would be automatically boosted by the increased pressure in the crankcase which operates the fuel pump)

    BUT ... supercharging a 2 stroke does not increase cylinder pressure in most instances because unlike a 4 stroke, the transfer (or "cylinder intake") port closes first while the exhaust port is still open - releasing any pressure increase to the exhaust pipe.

    So, even a 60,000 cfm leaf blower won't help beyond some slightly improved intake and cylinder scavenging
    Mark 75H,

    The cubic conversion you stated is incorrect 1 cubic foot = 1728 cubic inches. So 50 cubic inch = 0.028 935 185 2 cubic foot … and this is assuming a 100 % cylinder fill, we now can use your formula related to volume consumption via rpm.

    0.028 935 185 2 X 3 (# of cyl) = 0.0868055556 cubic feet

    0.0868055556 cubic feet X 6000 rpm = 520.8333335 cubic feet

    so at 6000 rpm assuming the engine is 100% efficient in cylinder fill it will use 520 cfm

    24 000 cfm will suck a person who is sitting in the boat into the motor… as this as much cfm as a small wind tunnel.

    But I do understand why adding positive pressure to a two stroke will not provide a benefit of increasing cylinder fill… Thanks for pointing that out.

    like i said before i dont know much about two-stroke engines but this rule will apply to any engine...

    Its best to learn form the guys who race, because they are the ones who know how to make it work!!!!! And that why i am part of this forum.

  9. #29
    Team Member Frank Volker's Avatar
    Join Date
    Dec 2004
    Location
    Washington, MO
    Posts
    67
    Post Thanks / Like

    Default

    The cubic conversion you stated is incorrect 1 cubic foot = 1728 cubic inches. So 50 cubic inch = 0.028 935 185 2 cubic foot … and this is assuming a 100 % cylinder fill, we now can use your formula related to volume consumption via rpm.

    0.028 935 185 2 X 3 (# of cyl) = 0.0868055556 cubic feet
    For a 50 cu in engine, the total swept volume is 50 cu in / revolution. Each cyl volume = (total displacement) / ( cylinder count ).

    0.0868055556 cubic feet X 6000 rpm = 520.8333335 cubic feet
    so at 6000 rpm assuming the engine is 100% efficient in cylinder fill it will use 520 cfm.
    Total = (50 cu in * 6000 RPM) / 1728 = 173.61 CFM.
    Per cylinder = 1/3 total = 57.87 CFM.
    If 2 carbs, 86.8 CFM through each.

    But I do understand why adding positive pressure to a two stroke will not provide a benefit of increasing cylinder fill… Thanks for pointing that out.
    Actually, it could help. Especially if you maintained the A/F ratio. A ton of factors come into play--port timings, reed type/stops, and especially the exhaust system, since the excess blow-through air/fuel would most likely change the exhaust system temperature, thereby changing the effective tuned length.

    like i said before i dont know much about two-stroke engines....
    Me neither, but I'm always willing to learn.

    Frank

  10. #30
    Team Member
    Join Date
    Feb 2008
    Location
    Canada, A little West and a little North of Toronto... Ya I'll tell Bill you say Hi!
    Posts
    8
    Post Thanks / Like

    Default 50ci for each hole?....whoops

    Frank,

    Thank you for pointing out my mistake… I made the calculation for displacement of 50ci in each cylinder….

    So what it should look like was this….

    0.028 935 185 cubic feet 2 X 6000rpm = 176.6111 cfm

    same as what you got

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Mercury Outboard Motors
    By Skoontz in forum Outboard Racing History
    Replies: 0
    Last Post: 10-23-2006, 08:10 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
  •