over size valves for the 450r sm?
  • abmjl
    Posts: 32
    Joined: Fri Jul 20, 2007 8:08 pm

    over size valves for the 450r sm?

    by abmjl » Thu Feb 25, 2010 10:03 pm

    ok i have to admit im a tinkerer and enjoy hiding in my shed filled with engeering machinary and i dont seem to be able to stop myself from trying to make my bike go faster n better, so now that ive said that my next brain storming idea was to put over size valves in the head to creat more flow.
    dont know wot my options are with this, so asking anyone out there have they done it or do they know anything about it, good or bad?

    current engine mods are-
    T4 header + pipe
    air filter + air box
    carb mods, needal, ac pump +bowl+leak jet , jets 180-190,
    power now
    stage 3 hot cam
    port/ polish head + extra valve angles+ planned 5 thou
    removed base gasket
    jd 2 stage ignision
    slip clutch

    going to bore out carb as well 2-3mm.

    any thoughts?
  • User avatar
    AgentSmith
    Posts: 14381
    Joined: Mon Apr 10, 2006 7:52 am

    by AgentSmith » Fri Feb 26, 2010 6:11 am

    You can go oversize with the valves up to 2mm+.

    There will be a point of diminishing returns though as the flow increases but the intake and exhaust velocity decreases.
    "Make a man a fire and he'll be warm for a day.
    Light a man on fire and he'll be warm for the rest of his life."
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  • abmjl
    Posts: 32
    Joined: Fri Jul 20, 2007 8:08 pm

    by abmjl » Fri Feb 26, 2010 11:55 am

    ok interesting, any idea where this point would be n wot i could expect if i was to do this, im unsure where the gains n loses would be.
    more top end rpm n pull?
    less torque n bottem end?

    the head is an 04 with the bigger intake valves n the top of ports where the valve spring seats above have been filled to remove the bump so its flat like the 07 head. some of the valve guide protruding into the port has been reshaped to.
  • User avatar
    AgentSmith
    Posts: 14381
    Joined: Mon Apr 10, 2006 7:52 am

    by AgentSmith » Fri Feb 26, 2010 12:37 pm

    abmjl wrote:ok interesting, any idea where this point would be n wot i could expect if i was to do this, im unsure where the gains n loses would be.
    more top end rpm n pull?
    less torque n bottem end?

    the head is an 04 with the bigger intake valves n the top of ports where the valve spring seats above have been filled to remove the bump so its flat like the 07 head. some of the valve guide protruding into the port has been reshaped to.


    Here's a hint:

    port shape and surface profile is MORE important than size.

    The idea is to make the fuel droplets as small as possible and keep them in suspension with the air as long as possible.

    Power is made in the combustion chamber and no where else. Getting as much finely dispersed fuel/air particles in as fast as possible and getting them back out as fast as possible is the real key to power.

    Sacrificing port velocity for volume will result in less efficiency, less power and worse throttle response.

    A wise man once said " Just because you have a bigger mouth, doesn't mean you can eat more..." :shock:
    "Make a man a fire and he'll be warm for a day.
    Light a man on fire and he'll be warm for the rest of his life."
    Image
  • abmjl
    Posts: 32
    Joined: Fri Jul 20, 2007 8:08 pm

    by abmjl » Fri Feb 26, 2010 1:00 pm

    i think i like that wise man, lol.
    ok im hearing ya. thanks for that info, thats the stuff i need to know.

    been trying to upload some pics but im an IT retard so having some trouble, any tips?

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