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Horsepower ratings (125cc motorcycle 33 hp!!! 123 cc chainsaw 8 hp)

Discussion in 'Chainsaw' started by hardhat, Jan 17, 2012.

  1. hardhat

    hardhat ArboristSite Operative

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    My partner today was talking about his 125cc motorcycle made 36hp at the rear wheel. I said no way and looked it up and the yz125 yamaha was rated at 33hp at the rear wheels. How is the possible when the 3120xp only makes 8.4 hp IIRC?

    Any thoughts on this. Perhaps water cooling allows you to dissipate heat faster and thus make more power for longer, but I can't see it quadrupling power producing ability. I just don't get it. Can anyone explain this?


    Larry
     
  2. 7hpjim

    7hpjim Addicted to ArboristSite

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    Longer stroke me thinks:eek2:
     
  3. funky sawman

    funky sawman Addicted to ArboristSite

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    Tune pipe, better carbs, and usually higher compression on bike engines, thats why:msp_thumbup:
     
  4. 7hpjim

    7hpjim Addicted to ArboristSite

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    You got Cape Buffalo in Idaho?:hmm3grin2orange:
     
  5. hardhat

    hardhat ArboristSite Operative

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    Cr 8.6:1 on yz 125. I think this is in line with the chainsaws. 54mm x 54 mm bore and stroke 124 cc

    3120 xp has a 60mm bore and 42mm stroke. 118cc.

    These numbers are different, but I cant see this counting for 4 fold increase in horsepower.

    Any how, why don't they do a little tweaking on the saw motor and double its output if indeed this is all that is different?
     
  6. BloodOnTheIce

    BloodOnTheIce Account Hold

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    125cc modern MX motor has the advantage of.
    -Boost ports
    -Case induction
    -Reed valves
    -Tuned pipes
    -34 to 38mm carbs
    -Power Valves
    -Full circle cranks
    -Thin ring pistons
     
    wyk likes this.
  7. mowoodchopper

    mowoodchopper Polar Bear

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    totaly diff engine, water cooled, reed valve, variable exhaust valve size, pipe, carb etc chainsaws are very weight limited on what the can do,and size, you dont want a pipe and a big carb with a huge air box on a work saw
     
  8. blsnelling

    blsnelling Site Sponsor

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    Yup, all of the above. A lot of compromises are made to fit the package of a chainsaw.
     
  9. 7hpjim

    7hpjim Addicted to ArboristSite

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    WOW he stayed @ a Holiday Inn Express last night!!:hmm3grin2orange:
     
  10. Hank Chinaski

    Hank Chinaski Number 37

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    besides, who the hell want's knobbies on their chainsaw??
     
  11. funky sawman

    funky sawman Addicted to ArboristSite

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    Aint got no buffler up here but we do have griz...
     
  12. 7hpjim

    7hpjim Addicted to ArboristSite

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    My BIL had a Winchester 70 in 375HH and the only thing we shot with it was a pine tree (pre CAD) and a groundhog, more of a novelty around here, I've shot a quite few big bores up to the 50BMG but never got to see the terminal results in anything bigger than prairie poodles, I'll bet that 500 will anchor them thar bares!!:msp_thumbup:
     
  13. funky sawman

    funky sawman Addicted to ArboristSite

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    HAA, it anchors the bears and myself very well:hmm3grin2orange:
     
  14. 7hpjim

    7hpjim Addicted to ArboristSite

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    Sorry to the OP but when I saw the smoke poles in the sawmans sig I couldn't help myself!.... 2 2 stroke smoke and smokeless powder for fun, only in America!!!!!:rock:
     
  15. lone wolf

    lone wolf Tree Freak

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    And dont forget more rotating mass!
     
  16. mp5n

    mp5n ArboristSite Operative

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    It's all about heat.

    It shouldn't be too difficult to get way more power from a saw motor, but you'll never be able to get rid of the heat without going to water cooling or modifying a cylinder and head with 4-5 times the fin area. Then how will you shroud everything and not have it be huge. You can probably get similar horsepower numbers from a race saw, but it'll never be able to run for any extended period of time. With a modern bike motor you have much more advanced porting, reed valves, carburation, ignition timing, exhaust systems and of course cooling systems. In my younger days I raced professionally and then built motors when I ran out of unbroken bones. I was running RM125s which I ran the compression at 225 psi with 36mm carbs. Way more than you'll find in any work saw.

    MP5N
     
  17. ridecaptain

    ridecaptain ArboristSite Lurker

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    i wonder why they use motorcycle engines to build hot saws?
     
  18. weimedog

    weimedog Addicted to ArboristSite

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    All this is possible because the designers of motorcycle competition motors have....more space and weight in the formula to work with. Not going to expand into a weimebook, but all things listed so far in this thread are possible in the MX world because they have the SPACE to work in and WEIGHT constraints allowing freedom in design solutions. Starting with cooling...if more power is to be had..more cooling is required. You have to have some foundations to build on to have more power...bore & stroke and the freedom based on casting size to have more port area, larger transfers, fancy intake and exhaust devices such as power valves & case reed induction systems...etc. Just goes on and on...expansion chambers.. I just can't see a chainsaw solution practical with water cooling & fans to get the air flow as they are static in operations, expansion chambers. 20plus pound motors making 30 plus hp can you just imagine what that would look like? Almost like blood's bike saw! With water cooling...:blob2:
     
  19. rwoods

    rwoods Addicted to ArboristSite

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    I haven't seen any hp numbers posted but I'm sure a 101B equipped MAC with a 35 mm carb is putting out way more than 8 hp even with a stock muffler. Not exactly a work saw but 101B's with chainsaw carbs were. I would bet they were putting out far more than 8 hp as well. I understand that heat was a real factor with these "hot" work saws. Ron
     
  20. z71mike

    z71mike Addicted to ArboristSite

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    Just to add to the cooling topic, as brought up a few times already.... Keep in mind, with a saw, you move your own air with the flywheel and it's usually warm air surrounding the saw. On a bike, you have multiple-mph airflow of fresh air that's relatively cool blowing by your heat sinks. Like the air-cooled Honda 400EX...... don't sit in one spot with the engine running too long or you'll easily overheat it. Just simple physics there. As weimedog said, it starts with the cooling and the ball rolls downhill from there.
     

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