The building of my vintage racer

Discussion in 'Airheads' started by FreeTheBeast, Apr 24, 2012.

  1. Voltaire

    Voltaire Titanium and Ceramic Hipster

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    Are you Moorespeed as in http://www.moorespeed.co.uk/ ?:clap
    Can you tell us about your racebike?

    Is it time for me to bin my 336 cam and move on?
  2. pommie john

    pommie john Long timer

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    So what is the consensus of a good power figure from a single plugged 750 full race engine?
  3. pommie john

    pommie john Long timer

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    I would say not. The 336 is a good cam.
  4. Boxer Metal

    Boxer Metal Mad Scientist

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    If you talking about horse power high 50's low 60's.
  5. pommie john

    pommie john Long timer

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    You want to try dual plugs, high 60s. :evil

    [​IMG]
  6. Boxer Metal

    Boxer Metal Mad Scientist

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    Is that a 750 or 1000?
  7. pommie john

    pommie john Long timer

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    750.

    It went to 92 hp when I took it out to 1000
  8. Boxer Metal

    Boxer Metal Mad Scientist

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    My best is 72HP. It gets expensive once you get over 50HP.
  9. pommie john

    pommie john Long timer

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    From a 750? I agree it get crazy money after a while. Mine started out as 750 but I took it out to 1000 after a season.

    The 68hp engine here had a 336, Venolia pistons ( the short ones, I bought from CC as they were called then) I can't remember what valves were in it but Jim Cray built it. As you can see on the graph it had Amal 38mm smoothbores and showed a slight improvement with 38mm Dells.
    There wasn't too much else in the engine, modified oil system of course.
  10. Boxer Metal

    Boxer Metal Mad Scientist

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    For me it was a set of my own pistons, sport cam, larger valves, porting the heads, 36mm round slide carburetors and the biggest improvement was a 2/1 exhaust that I designed.
  11. pommie john

    pommie john Long timer

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    I never had much luck with 2:1 exhausts. I made one that made decent power at the top end but it had a big hole in the torque in the mid range.
    The simplicity of a 2:2 with something like a Supertrapp on the end has a lot going for it. Somewhere I have dyno charts comparing them. I'll dig them out in the next few days.
  12. Boxer Metal

    Boxer Metal Mad Scientist

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    We lost 5-7Hp with off the shelf 2/1's and we gained almost 10HP with mine. Merged header and a big collection pipe before the muffler.
  13. pommie john

    pommie john Long timer

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    Was it a bit like the Gordon Blair Norton pipe? Very short headers, maybe 16" long into a single collector at least twice the length of the primary?
  14. Boxer Metal

    Boxer Metal Mad Scientist

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    I wont give out the specs but here is what it looked like.

    [​IMG]
  15. moorespeed

    moorespeed Adventurer

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    yes i am the moorespeed, and i have never had less than 74hp at the rear wheel short stroke or standard stroke . the short stroke starts to pull from 6400 and makes max power at 9450, the standard stroke is about 1000rpm less. i have my own pistons 83mm and 88mm.
  16. pommie john

    pommie john Long timer

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    Interesting. Surprisingly long primaries.
  17. bill42

    bill42 Old-School BMWs

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    How much approximately is the actual horspower of a 1981 R100 motor that BMW rated as having 70HP at the engine?
  18. Airhead Wrangler

    Airhead Wrangler Long timer

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    Probably about 55-60... downhill... with a tailwind.
  19. Boxer Metal

    Boxer Metal Mad Scientist

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    The driveshaft eats up 20% so that would take it from 70hp at the flywheel to 56hp at the rear wheel.
  20. supershaft

    supershaft because I can

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    How much actual hp at the crank? I know of no one that has measured the power at the crank other than the factory. I suspect there rating is a bit high but they don't stretch the truth near as much as many manufacturers. At least here in the states I think the only airhead rated that high was '77 RS's half way into the '78 model year? I think a US '81 R100 was rated at 67?

    I don't think our drive line eats up 20%. Oil alone makes a big diff but . . . . It's close! Different dyno's read different figures. It all depends on the dyno AND operator. The dyno I was around that dynoed a lot of airheads you were super lucky to get 56hp. Most were from 48 to 54hp and that's R100's.