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Re: Questions about Pistons,Displacement.Compression Ratio, and 92 Premium Octane

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  • Julian Bond
    urco Sat, 31 Dec 2005 19:31:02 ... oooh, oooh, oooh, Pegaso RS125. Any pictures? -- Julian Bond E&MSN: julian_bond at voidstar.com M:
    Message 1 of 28 , Jan 1, 2006
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      urco <kev193xm@...> Sat, 31 Dec 2005 19:31:02
      >---ESSP, Have you cross-referenced mods to the Aprilia Pegasso
      >motor, which I believe is essentially the same, but runs a pair of
      >33mm flat-slide carbs, at least the one fitted in my mates Aprilia
      >RS125 has them as standard fitment. KP

      oooh, oooh, oooh, Pegaso RS125. Any pictures?

      --
      Julian Bond E&MSN: julian_bond at voidstar.com M: +44 (0)77 5907 2173
      Webmaster: http://www.ecademy.com/ T: +44 (0)192 0412 433
      Personal WebLog: http://www.voidstar.com/ skype:julian.bond?chat
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    • Ray & Sonja Crenshaw
      ... One thing to think about (not that you haven t) is that a BIG SINGLE has a severely limited (relative to multis) RPM-range. Of course, the upper range is
      Message 2 of 28 , Jan 1, 2006
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        > They were 5 valve single plug/exhaust port engines vs 4 valve
        > 2plug/2exhaust port on BMW F650.

        One thing to think about (not that you haven't) is that a BIG SINGLE has a
        severely limited (relative to multis) RPM-range. Of course, the upper range
        is limited because of the large pokey-whirley bits that come with a large
        cylinder displacement. But then there's the bottom-end revs...

        On MOST modern (haven't ridden the Bimmer thumper) big singles, the flywheel
        mass is VERY low, which makes for Chain Snatch To Beat The Band. Well, I
        don't think your bike has a chain, but it's likely your engine is still
        "nervous" under about 3,500 rpms. Lacking a 45-pound flywheel, it's the
        nature of the beast.

        I've ridden a bunch of big singles (and twins), but nothing like ALL the
        ones out there and--oddly enough--I find that they ALL have this
        chain-snatch up to around 3,000 rpms, clearing above that. The larger the
        individual cylinder displacement, the worse the snatching; and the wider the
        "really bad" range above 3-grand. Still, they seem to clear up by 3,500 or
        so. Okay, my point...

        ASSUMING your Bimmer is uncomfortable below 3,500 rpms (my Honda XL600R is
        sickeningly unpleasant at anything below 48-mph in 5th gear), this gives you
        the freedom to add a mild cam to the bike since... (hold onto your hats
        now...)

        YOU DON'T CARE IF THE BOTTOM-END POWER TAKES A NOSE DIVE!!!

        See? So as long as the carburetion is steady down there (so you can at least
        get rolling in 1st gear), who cares if you throw away 6-lb/feet at 3-grand?
        You can't really ride it below 3,500 anyway!

        Plus, you don't NEED a cam hot enough to allow it to breathe at 9-grand
        since YOU AIN'T HEADED THERE EITHER! (pardon the caps, I ain't shoutin', I'm
        typing parenthetically without the benefit of parentheses)

        Good breathing between 4k and 7k is where it's at on a big single. Well, at
        least that's my opinion for street riding. With just a few breathing mods
        (mostly exhaust, I'd think) a "warm" cam can add more between 4k and 7k than
        almost anything else you could do. This from a big single lover who
        currently has about 7, and has owned an additional 3-or-4 others over the
        years.

        I am the guy from whom you apparently took offense when I told you how
        difficult it was going to be to get much more than 5-8 additional horses
        without the bike being louder than a cannonfire. I wish you the best, and
        I'm pulling for you, but I stand by my original assertion. Bear in mind, we
        won't know if I'm right unless you get a chassis dyno readout of the bike in
        its current state, then compare it with whatever you end up doing.

        Dynos vary (usually on purpose), but realistic rear-wheel horses from a
        street-legal 650 single would strain to break the 35-38 mark. Therefore, a
        4-hp improvement would be a SUBSTANTIAL 10% increase. I think my SR500
        Yamaha (2-valve head, 34mm carb; well-tuned, but stock) has about 25 hp...
        and so does everyone elses!

        Best to you all this year of 2006,

        jrc in SC
      • essp2003
        On MOST modern (haven t ridden the Bimmer thumper) big singles, ... Bimmers are cars and Beamers are motorcycles. ... SINGLE has a ... upper range ... large
        Message 3 of 28 , Jan 1, 2006
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          "On MOST modern (haven't ridden the Bimmer thumper) big singles, ..."

          Bimmers are cars and Beamers are motorcycles.



          --- In mc-engine@yahoogroups.com, "Ray & Sonja Crenshaw"
          <raymanz93@g...> wrote:
          >
          > > They were 5 valve single plug/exhaust port engines vs 4 valve
          > > 2plug/2exhaust port on BMW F650.
          >
          > One thing to think about (not that you haven't) is that a BIG
          SINGLE has a
          > severely limited (relative to multis) RPM-range. Of course, the
          upper range
          > is limited because of the large pokey-whirley bits that come with a
          large
          > cylinder displacement. But then there's the bottom-end revs...
          >
          > On MOST modern (haven't ridden the Bimmer thumper) big singles, the
          flywheel
          > mass is VERY low, which makes for Chain Snatch To Beat The Band.
          Well, I
          > don't think your bike has a chain, but it's likely your engine is
          still
          > "nervous" under about 3,500 rpms. Lacking a 45-pound flywheel, it's
          the
          > nature of the beast.
          >
          > I've ridden a bunch of big singles (and twins), but nothing like
          ALL the
          > ones out there and--oddly enough--I find that they ALL have this
          > chain-snatch up to around 3,000 rpms, clearing above that. The
          larger the
          > individual cylinder displacement, the worse the snatching; and the
          wider the
          > "really bad" range above 3-grand. Still, they seem to clear up by
          3,500 or
          > so. Okay, my point...
          >
          > ASSUMING your Bimmer is uncomfortable below 3,500 rpms (my Honda
          XL600R is
          > sickeningly unpleasant at anything below 48-mph in 5th gear), this
          gives you
          > the freedom to add a mild cam to the bike since... (hold onto your
          hats
          > now...)
          >
          > YOU DON'T CARE IF THE BOTTOM-END POWER TAKES A NOSE DIVE!!!
          >
          > See? So as long as the carburetion is steady down there (so you can
          at least
          > get rolling in 1st gear), who cares if you throw away 6-lb/feet at
          3-grand?
          > You can't really ride it below 3,500 anyway!
          >
          > Plus, you don't NEED a cam hot enough to allow it to breathe at 9-
          grand
          > since YOU AIN'T HEADED THERE EITHER! (pardon the caps, I ain't
          shoutin', I'm
          > typing parenthetically without the benefit of parentheses)
          >
          > Good breathing between 4k and 7k is where it's at on a big single.
          Well, at
          > least that's my opinion for street riding. With just a few
          breathing mods
          > (mostly exhaust, I'd think) a "warm" cam can add more between 4k
          and 7k than
          > almost anything else you could do. This from a big single lover who
          > currently has about 7, and has owned an additional 3-or-4 others
          over the
          > years.
          >
          > I am the guy from whom you apparently took offense when I told you
          how
          > difficult it was going to be to get much more than 5-8 additional
          horses
          > without the bike being louder than a cannonfire. I wish you the
          best, and
          > I'm pulling for you, but I stand by my original assertion. Bear in
          mind, we
          > won't know if I'm right unless you get a chassis dyno readout of
          the bike in
          > its current state, then compare it with whatever you end up doing.
          >
          > Dynos vary (usually on purpose), but realistic rear-wheel horses
          from a
          > street-legal 650 single would strain to break the 35-38 mark.
          Therefore, a
          > 4-hp improvement would be a SUBSTANTIAL 10% increase. I think my
          SR500
          > Yamaha (2-valve head, 34mm carb; well-tuned, but stock) has about
          25 hp...
          > and so does everyone elses!
          >
          > Best to you all this year of 2006,
          >
          > jrc in SC
          >
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