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ms 461 woods port race thing

Discussion in 'Chainsaws' started by tree monkey, Jan 12, 2018 at 5:08 PM.

  1. maulhead

    maulhead Pinnacle OPE Member

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    So says the instigator....:D
     
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  2. tree monkey

    tree monkey ONE OF THE GREATEST!

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    went to town, got battery, good to go

    it's about 4 tenth slower then the best time I had yesterday. felt better
     
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  3. paragonbuilder

    paragonbuilder ONE OF THE GREATEST!

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    Is that with the stock piston? Still need to raise exhaust?
     
  4. XP_Slinger

    XP_Slinger Pinnacle OPE Member

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    That time difference could be the knots in the cants too. I did notice that it’s not 4 strokin as hard compared to the previous video.
     
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  5. drf256

    drf256 Giant Member (and Fartknocker)

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    I'm likely wrong.

    I'd open the secondaries a bit later to allow more pressure in the primaries before they vent it. Looks like the primaries arent generating enough pressure and the flow is sluggish.

    May also tell you that you have another piston to grind. IIRC, you made one to vent the secondaries, but not the primaries. Edit-you made both.

    I see fresh charge coming out of the exhaust. I'd tighten the primaries with JB on the ex side.
     
  6. paragonbuilder

    paragonbuilder ONE OF THE GREATEST!

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    How much offset do you give the primaries Doc? He’s got 7 deg right now.
     
  7. Terry Syd

    Terry Syd Pinnacle OPE Member

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    I love this kind of R&D. You know from taking it one step at a time and then 'going too far', what really works. I never threw away an old piston, I could always use them for testing.

    It is more time consuming than 'just give me some numbers', but you can have confidence in the results.
     
  8. tree monkey

    tree monkey ONE OF THE GREATEST!

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    same piston as the last test, only changed the intake port


    wood is not the best, was hopping it would get better, but I don't think it will. gotta depend on me feeler a little
     
  9. Terry Syd

    Terry Syd Pinnacle OPE Member

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    Shocking amount of 'short-circuiting' going out that exhaust port. If you can get that fixed, I'd expect a bit of a bump in power and fuel economy.

    That pattern on the piston of the primary transfers goes to show how important the angles are in the walls of the transfer ports. Most guys just worry about 'numbers' when a change in the angles could net them even more.

    If you can reform the tunnel and the angle closest to the exhaust port to turn it more towards the back wall, it may help correct the short-circuiting. Even if the tunnel becomes a bit larger than you want, the exit of the port (especially when it first cracks open) could fix the problem.

    Years ago, and it was included in Blair's work, there was some porting done to a series of Yamaha DT 25o jugs. They kept the same time/area of all the ports (exhaust, transfer and intake), but changed the port configurations and angles. The difference between the best and worse performance was a cool 15% difference in power. That difference was across virtually the entire powerband.

    I look forward to a picture of the pattern on the piston after you finish porting.
     
  10. CR888

    CR888 Pinnacle OPE Member

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    Graeme Bell likes this reversible style of approach to porting....after all pistons are MUCH cheaper than cylinders. I like it!
     
  11. tree monkey

    tree monkey ONE OF THE GREATEST!

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    a little more ex timing
     
  12. Terry Syd

    Terry Syd Pinnacle OPE Member

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    Here's a thought, you may be reducing the short-circuiting by increasing the blow down. If the cylinder pressure and exhaust flow is reduced by the time the transfers open, there may be less influence on the transfer flow. - However, if the short-circuiting is reduced, then you may not need as much blow down.
     
  13. tree monkey

    tree monkey ONE OF THE GREATEST!

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    we are thinking alike. time is my problem here. I only have 2 days to get it done. I need to chase the results. witch tell me more ex. it was turning 16320 last run
     
  14. drf256

    drf256 Giant Member (and Fartknocker)

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    So you’re thinking that the piston is showing low pressure or backstuffing overall?

    How do the uppers look? Is there coking?

    If you raise the ex roof too much, won’t you lose swept volume and power stroke?

    You may be at the end of what you can get from it. Maybe more Blowdown on all 4 uppers and that’s it?

    You coulda actually “Maxed the jug out”
     
    Last edited: Jan 14, 2018 at 5:15 AM
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  15. drf256

    drf256 Giant Member (and Fartknocker)

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    I was thinking to reduce it or make em flat.
     
  16. Terry Syd

    Terry Syd Pinnacle OPE Member

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    There is an alternative. Some jugs have the primaries with an sloping top roof. That is, the corner opening nearest to the exhaust port is LOWER than the corner near the center of the cylinder.

    That allows the port to get flowing in the right direction before it opens near the flowing exhaust port.

    Maybe on the next jug, when notching the piston top during testing, the notch can be lower in the center to simulate a sloping transfer roof. If it works out, then after playing with the slope on the piston top, it can be duplicated into the transfer roof.
     
  17. tree monkey

    tree monkey ONE OF THE GREATEST!

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    i'm not concerned with back stuffing

    can't see any

    yes I can and will go to far, that's the idea of the cut pistons, being able to back up

    will be changing piston next. raise secondary's

    maxes out jug is a loaded term, lol
     
  18. drf256

    drf256 Giant Member (and Fartknocker)

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    Yes Terry.

    I’ve seen most Stihl quads open like an ^ as you look in towards the band.

    The angles have more to do with flow than the numbers.

    That’s why so many guys are generous with the “gimme the numbers” requests.

    I spend more time now on the transfer roofs than I do on the entire rest of the cylinder.
     
  19. drf256

    drf256 Giant Member (and Fartknocker)

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    All I’m saying is that at some point, you’ll get dimishing returns with any change. You may be there. I’m sure you’ll keep trying.

    Could the wash at the Ex port be the loop over scavenging and not the primary output being pulled out by Venturi effect?
     
  20. tree monkey

    tree monkey ONE OF THE GREATEST!

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    raised ex again, no gain or slight loss. time for a different piston. that will back up the ex port
     
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