1973 Honda CB350 - how much power?

Discussion in 'Motorbike Technical Discussion' started by Ig, Mar 13, 2007.

  1. It does seem to have eluded you, though.

    Makes *no* difference whatsoever. Power is power, and if you don't have
    enough power to pull a taller gear, not even dilithium crystals will

    I stand by my previous assessment. You are a stupid sod.
    The Older Gentleman, Mar 16, 2007
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  2. <VBG>

    No, it doesn't. You're giving us a lot of amusement, though. Please keep
    The Older Gentleman, Mar 16, 2007
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  3. In stock trim? Maybe 75mph. I've had a few dozen CD and CB175s, which
    aren't so different in terms of size, weight and power output.

    Screens and fairings make precious little difference at that sort of
    speed, except to rider (dis)comfort.
    The Older Gentleman, Mar 16, 2007
  4. Nice. I see where one guy got 140+ out of a 100cc motor, and the highest
    in the 350cc class of just over 189. I ran a "go cart" race track for a
    while, we used 100cc McCulloch racing motors, with 12" tires we could
    squeeze out a top speed of about 107...but those motors were finicky and
    had to be torn down and rebuilt just about every day.

    I bought my CL used and I don't know if it had been bored out previously,
    or any other mods of that nature. I just tuned it and changed out the rear
    sprocket and the chain. Unfortunately, I crashed that one and the frame
    wasn't salvageable. (The Docs didn't think *I* was salvageable either, and
    told me I'd never walk again, but I fooled them.)
    Zaphod Beeblebrock, Mar 16, 2007
  5. OK, have it your way. Practical and professional experience rebuilding
    motors and racing since age 12 counts for nothing and is negated by your
    theoretical calculations. Nobody has ever taken a 350/360cc motor to 120+,
    if you say it can't be done, then it can't be done. I bow to the awesome
    power of your mind which has the ability to cancel reality.

    Why don't you tell that to these guys, that the one with the 350 didn't go
    to 189, and the other guy with the 100cc motor didn't go to 140:


    (Thanks to Rick Cortese for the link.)

    120mph out of a CL360 is not particularly difficult. 189, on the other
    hand, takes a bit more doing.
    Zaphod Beeblebrock, Mar 16, 2007
  6. Ig

    Mark Olson Guest

    Ah, the old 'appeal to authority' argument. Never fails, when you can't
    weasel out of some bullshit you tried to pull, the old, 'I've been doing
    this for years, why do you doubt me' wheeze. I've got news for you, there
    are people on this newsgroup that actually do know what they are talking
    about and you are making yourself

    Nope. I never said a 350/360cc engine couldn't get to 120mph. What I did
    say, was your stock CL360 didn't do it, can't do it, because it was a
    stock bike without any sort of engine mods or fairing on it. Changing
    the sprockets doesn't make your bike 'custom', if you want to cling to
    that 'mod' as somehow elevating your CL360 to non-stock, fine. But it
    doesn't change how much power the engine puts out, and if the power isn't
    there, it won't get to 120 mph, no matter how much you want it to.
    Do you know what those various class designations mean? Somehow I doubt
    a stock 100cc bike is going to hit 140, and I will bet my life that the
    189 mph 350cc bike was a streamliner. But keep on ignoring the fact that
    your CL360 isn't a streamliner, as TOG says, you keep on showing how
    little you know about bikes and simple physics.
    Go on. Get 120 mph out of your CL360. It *can* be done. But it won't
    be done simply by changing the sprockets and giving the bike a tune up.
    Mark Olson, Mar 16, 2007
  7. No, it doesn't. Try riding a few bikes, and by a few, I mean 'several
    hundred'. Dunno about Mark, but I reckon I've owned something like
    250-300 bikes in the last 30+ years, and ridden probably another
    couple of hundred. This tends to give one a fairly empirical and
    accurate view.

    Oh, it can be done. The CB350 is quite keenly sought after by the
    classic racing boys here in Europe, and can be tuned to go
    surprisingly quickly. What Mark is saying, and what I'm saying, is
    that a couple of basic mods will not make one do 120. It just won't.

    As a very rough rule of thumb, production road bikes need something
    like 28-30bhp in order to reach 100mph. To get to 120, you need about
    60bhp. Obviously there are other factors here, like the bike size:
    Honda racing 125 two-strokes will hit high speeds on considerably less
    than 60bhp, but we're talking road bikes here.

    The old 360 twin made a claimed 34bhp, in an era when bikes weren't
    routinely dyno tested. Assuming something like 25-28bhp at the rear
    wheel gives it a top speed of round about 100 - a good one might do
    it, and an average one might not, but let's be generous.

    To get 120 out of one, you'd need to raise the rear wheel horsepower
    to around 50bhp, given the size/bulk of the old 360. Take the Ducati
    750SS in my(other) sig: that has a claimed 64bhp and will do
    125-127mph, according to differing road test measurements. Most I have
    ever seen on the clock is 125: a racer friend managed 130. I reckon
    rear wheel horsepower is about 55-60bhp. So we're talking about a bike
    that's twice the capacity, nearly twice the rated horsepower, which
    manages a mere 5-10mph faster than you claim for your old shonker.

    Sorry, you're living in a dream world, unless you paid for some very,
    very expensive surgery. Or had a speedo that was more inaccurate than
    usual. Or conceivably, laced a smaller diameter front rim to the hub,
    which would cause the speedo to do silly things.
    These are pukka race/record breaking bikes, you utter imbecile, not
    played-with soggy old Honda road twins.
    Yes, it is.

    Right, your basic ignorance of physics and other things have been
    adequately pointed out. Other matters like faulty insturments have
    been flagged up. If you're not prepared to admit you've made a howling
    monkey of yourself, not prepared to admit that your speedo might be
    lying as much as your President, and not prepared to admit you might
    be in error, what does that leave?

    Fancy running for President?
    chateau.murray, Mar 16, 2007
  8. That motor had the power. And it wasn't a fluke, I did it to two different
    CL360s and it didn't take a whole lot of work to do it.

    I will respect the other gentleman's high opinion of you and not respond
    in kind to your repeated insult, though I would have thought that if you
    were truly the sort he claims you would have the wisdom not to maintain
    such a stubbornly entrenched position. Just because *you* cannot conceive
    how a thing can be done doesn't mean that it can't be done.

    If you have taken the time to peruse the link that Mr. Cortese so kindly
    provided, you will have seen that my paltry 120mph out of that particular
    machine pales in comparison to what others have done.

    While you're talking about power, consider that power alone is not the
    only factor- there's the power-to-weight ratio.

    As far as wind resistance- scootching back on the seat, feet on the rear
    set of pegs and literally lying down on top of the fuel tank with elbows
    tucked in cuts the drag considerably.

    This conversation reminds me of a guy who swore up and down that it was
    *impossible* to run a V-8 motor using three 2bbl carbs, even while looking
    at the motor in operation.

    You can continue calling me a "stupid sod" if you like, but I would
    suggest that it may reflect more poorly on your character than mine.
    Zaphod Beeblebrock, Mar 16, 2007
  9. No, it didn't.
    No, you didn't.
    As I said, for dedicated record-breaking or race machines. Different
    animals. You've been told this, so I can only assume that you're
    trying the point again out of desperation.
    God, you are ignorant. Weight hardly affects top speed. It affects
    acceleration. This was told you earlier in the thread.[1]
    OK, sweetie. Do you know how motorcycle magazines achieve their top
    speed figures? They get the smallest tester they can find, and dress
    him in skin-tight leathers. Top speed runs are effected by doing
    exactly what you say - flat on the tank, and with naked bikes, if you
    dare, left hand off the bars and gripping the fork leg. Mirrors are
    frequently removed.[2] And nope, no way will you get a CB360 to do 120
    with the mods you suggested, unless you're going down a very, very
    steep hill with a hurricane tailwind.

    If a mag gets an utter max of 100mph, then the average Joe can expect
    Not the same thing at all.
    Nope, it's an accurate reflection of your intellect. Erring on the
    kind side, if anything.

    [1] More than 20 years ago, Bike magazine here in the UK did a very
    interesting exercise involving (IIRC) a Honda VF400 and a number of
    staff members, ranging from Roland Brown (then a staffer, now an
    international freelance) who stood six feet four in his socks and
    weighed 160lbs or so, and at the other end, editorial assistant Ione
    Holmes (five feet one and 112lbs or so)[3]. Top speed runs,
    electronically timed, were within a couple of mph of each other.
    Quarter-mile times varied immensely, in favour of the small girl, who
    had little experience of quarter-miling. I've got the copy in my
    [2] Guess how I know this?
    [3] They married each other, believe it or not.
    chateau.murray, Mar 16, 2007
  10. Ig

    Mark Olson Guest

    Hmmm. How do the 300km/hr or 186 mph bikes (limited by manufacturer's
    agreement, some capable of exceeding 200 mph) get going that fast, with
    less than 176 hp?
    Doesn't the power required to overcome aerodynamic drag increase as
    the cube of the velocity? <cheats, via google> Yep.

    This guy (if you squint hard) has a spreadsheet


    that says for some particular bike & rider, it takes 18.2 hp to go 75, so
    to go 120, it takes...

    e(3*l(120/75)) * 18.2

    about 75 hp.

    With 11 hp, that mythical bike would go about...

    75 * (e(l(11/18.2)/3))

    63 mph. You are a genius!

    Assuming our favorite bike, the CL360, with an advertised hp of 34 at the
    crank, IIRC, has all of that available at the rear wheel, and it's roughly
    the same frontal area and coefficient of drag:

    75 * (e(l(34/18.2)/3))

    It's going to go about 90 mph tops.


    1/4 the hp to go 1/2 as fast? I think you mean 1/8 the hp to go 1/2 as
    Mark Olson, Mar 16, 2007
  11. Amen.
    The Older Gentleman, Mar 16, 2007
  12. I'd query those figures: a decent 14bhp 125 will hit 75, and the
    original Honda CB750 did 120+ on a claimed 67bhp.

    Pretty close, though.
    The Older Gentleman, Mar 16, 2007
  13. Ig

    Mark Olson Guest

    I didn't look too closely to figure out what sort of bike he was modeling.
    Maybe it was a tourer with a big fairing and windshield. Actually,
    my ZG1000 does about 127 tops, with 91 hp at the wheel, and using the
    mythical 75mph/18.2hp bike as the model:

    e(3*l(127.2/75)) * 18.2

    It agrees rather well with their measured dyno reading of 91.0 hp peak,
    assuming that the top speed actually occurred at the exact power peak,
    which can't be guaranteed of course, due to gearing (I wonder if Mr.
    CL360 will jump up and claim he can get my ZG to go another 10 or 20
    mph faster if I change out the final drive :)
    That's the point, it's close enough.
    When the power required increases as the cube of the speed, and you
    know you've got 34 hp at the most to work with, knowing a little bit of
    1st year physics[2] won't let you wiggle out with a simple hand-wave.

    It's easy enough for anyone who's ridden a few similar bikes up to their
    real world top speeds, and knows where to dig up dyno numbers for them,
    to conclusively prove that without major modifications to power output
    or to the coefficient of drag, and/or frontal area, a similar bike isn't
    going to magically be the lone exception to the laws of physics.

    [1] 127 and 91 hp,
    http://www.aquariumfish.com/mcn/model_eval/Kawasaki Concours, Part 4.pdf

    [2] Of course if you don't know physics and can't do simple maths,
    you can be untroubled by such concepts, and believe anything you want.
    Mark Olson, Mar 16, 2007
  14. Yep.

    I've owned *a lot* of small low-powered bikes. I just like playing with
    them. In fact, I've just bought a 1974 Honda SL125, which I'm planning
    to restore to "rather nice" condition....

    Anyway, you don't even need to dig up the dyno numbers. After a while,
    you hop on something and have a pretty good idea how it'll perform.

    You still get exceptions to the rule - my 1988 Yamaha RD350 power-valve
    was one. Christ, that was a fun bike. Claimed 60bhp: easily pulled into
    the red in top, at an indicated 120+.

    I actually geared it up, and it still pulled it (I'd heard it was
    capable of doing so) but the "odd spot" at 6000 rpm (when the
    power-valve was making its mind up whether to open or not) moved from
    70+ mph to 75+, which made it a real pain, so I put the gearing back to

    Thereby proving, I suppose, that the OE manufacturer usually gets it
    The Older Gentleman, Mar 16, 2007
  15. Ig

    Mark Olson Guest

    The aerodynamic drag force increases as the square of the velocity, which
    makes the power increase by the cube of V.

    Despite Wikipedia's dubious reputation, I am pretty sure they've got
    it correct, I didn't explicitly quote them before, but since the
    question was raised:


    (Apologies if the character encoding gets screwed up)

    The power required to overcome the aerodynamic drag is given by:

    Pd = Fd (dot product) v = -1/2 Ï v^3 A Cd

    Fd is the force of drag,
    Ï is the density of the fluid (Note that for the Earth's atmosphere,
    the density can be found using the barometric formula. It is
    1.293 kg/m3 at 0°C and 1 atmosphere.),
    v is the velocity of the object relative to the fluid,
    A is the reference area,
    Cd is the drag coefficient (a dimensionless constant, e.g. 0.25 to 0.45 for a car), and
    [v] is the unit vector indicating the direction of the velocity (the
    negative sign indicating the drag is opposite to that of velocity).

    The important bit is the v^3.
    Mark Olson, Mar 16, 2007
  16. Ig

    oldgeezer Guest

    They tought me that some 40 years ago.
    It still is correct.

    Cd relates to the shape of the body. A square block
    has a higher Cd-value than a smoothly curved

    btw, the CD-value for a body is simply measured (in a wind tunnel).
    They place the body in an airstream and
    measure the force needed to keep it
    in place.
    Cd is then calcultated by
    dividing that force by
    'half rho v-squared times A' (I cannot type
    better than this).

    The term 'reference area' sounds
    a bit misleading to me.
    It is just the area of the cross section in the wind. Like the frontal
    area of a car. Or the frontal area of you and
    the bike together. In square meters.

    Laying flat on the bike thus helps in
    two ways. You lower both Cd and A.

    It always amuses me when a car manufacturer
    proudly states a low Cd for the car, and forgets
    to mention anything about
    the A.
    oldgeezer, Mar 17, 2007
  17. Ig

    Mark Olson Guest

    That's quite clear, (except for "times a work" should be "times THE
    work") and I see nothing wrong with it.
    All I will say is in my experience, cars don't typically burn 4x as much
    gas at 60 mph than they do at 30 mph... but it does indeed take 8x as
    much power _to overcome aerodynamic drag_ at 60 mph as it does at 30 mph,
    _assuming their equation holds true_ at those sorts of speeds.

    The critical sentence in that paragraph gives them enough wiggle room
    to push an elephant through:

    "It should be emphasized here that the drag equation is an
    approximation, and does not necessarily give a close approximation
    in every instance. Thus one should be careful when making
    assumptions using these equations."

    I had stayed in Aero Engineering instead of the engineering major I
    did pursue, I could talk about this with a bit more certainty, but I
    am not in any doubt about the likelihood of a stock engined CL360
    attaining 120mph without going downhill and/or pushed by a tailwind.
    Mark Olson, Mar 17, 2007
  18. See my remark about removing the mirrors when speed-testing bikes.
    The Older Gentleman, Mar 17, 2007
  19. Ig

    Gene Cash Guest

    Oh crikey. How did this twit escape from my killfile?

    Did the "tinkering" also include painting new numbers on the speedometer?

    Gene Cash, Mar 17, 2007
  20. Heh. welcome to the party.
    The Older Gentleman, Mar 17, 2007
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