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Toque, Power, Detuning And Powerband.

Discussion in 'Technical and Troubleshooting Torque' started by FALCON-LORD, Aug 11, 2008.

  1. There is a common argument about power Vs Torque With some people quoting peak power and others talking about Torque curves.
    So what are the variables?
    From what I gather less cylinders gives you a flatter torque curve, but peaks out at less revs giving you less peak power. More Cylinders needs to be revved more before it gets into the meat of the torque, but can spin to huge power numbers.
    Then there is the word Detuning. Now before we look at this question I will state as a public service announcement that you should never mention this in front of VTR Elmarco, or you probably get a punch in the mouth.
    What does it achieve? It makes the bike less powerful, but does it mean you also get better torque down low?

    And last of all.
    Can you broaden the Body of the Torque curve without changing the physical attributes of the engine?
    Is it all about Bore and Stroke? Or can you use timing and exhaust tuning to give a peaky bike a better low end toque profile?

  2. I know nothing about this sort of stuff.

    Bore/stroke & number of cylinders will not give you a determining result.
    Ie: Offroad singles (Suzuki RMZ250) can scream out big ponies up top of their rev range.

    ‘Detune’ is a one word explaination to best convey what an engine has expereinced. It doesn’t mean it’s lost power overall, it just means that the power curve has been changed.

    An example can be my 900 Hornet. It runs a ’98 Fireblade engine in it & it has been ‘detuned’, but that ‘detuning’ has given me the sort of top gear, two-up , roll on accelleration that the ’98 Firelbade would not be able to manage (as effectively).
    Also it’s real easy going & this translates to being able to ride dirt/gravel roads like it was a big traily – which is a good thing.

    Sometimes outright power is not a desirable thing & to make a bike ‘more ridable’ you be looking a changing it’s power curve to present healthy power sprerads in the engien rev ranges where you need it (or spend the most of your time in).
  3. retarding the timing will give you better low and mid range toque at the expense of top end power.

    when i had the heads off the XR i did this by two teeth. the engine was detuned as it is, this gave it serious bottom end surge, but made it actually unproductive to rev it past around the 6 grand mark. next time i have the heads off i will advance by the same just to try.
  4. To make a generalisation, a 'Tuned' engine could be considered as one which has been optimised for the sole purpose of producing maximum power.

    Therefore, a 'detuned' engine is one where they've backed it away from "maximum tune" to chase other characteristics, such as a broader torque curve or more power at low rpm.

    Detuning can be/is done by changing things such as:
    * Camshaft timing (advancing/retarding the camshafts)
    * Camshaft duration & lift (changing the shape of the camshafts)
    * Intake and exhaust runner lengths (changing the length/diameter of the runners)

    Edit: I don't list ignition timing and fuelling because modern ECUs can be programmed to give optimal power for a given engine speed without affecting the performance throughout the rest of the range. Programming the ECU to give you less power is not 'detuning', because there's no benefit except if you're trying to electronically 'flatten' the torque curve to make it more predictable.

    I think it would be rare that the piston bore/stroke would be modified for the sake of detuning. That's a bit on the 'extreme' side.

    Interesting to note that variable-intake systems such as T-VIS on the Toyota 4AGE engine, and variable-camshaft systems such as VVTi-L and VTEC alter the camshaft and intake geometry for this exact purpose - they dynamically 'detune' the engine at low RPM and then 're-tune' the engine as the engine speed picks up!
  5. Massive question.

    Basically it comes down to capacity and state of tune. To get it clear from the start, what I mean by state of tune is; at what point in the rev range does the bike produce it's peak power?

    There are two areas of misinformation out there in this area. Firstly number of cylinders. Due to some prolific poor journalism, many people believe that less cylinder = more torque. it's not true. Less cylinders = a forced lower state of tune and/or a compensating larger capacity = more torque.

    The second area of misinformation is bore vs stroke. A longer stroke gives more torque, but only if the capacity increases. If the bore is sacrificed for a longer stroke to keep capacity the same and combustion pressure stays the same and state of tune stays the same then peak torque stays the same.

    Generally. and this is where it turns into a really big question. e.g. if stroke gets too short, then the intake time becomes too short and you don't get good cylinder filling and therefore don't get good combustion pressure and therefore torque drops off. Alternatively if stroke gets too long, the cylinder gets too hard too fill and pressure drops . . . .

    Can you broaden the torque curve of a production bike? playing with cam timing (advance and retard), intake lengths and exhaust lengths can give you quite a bit.

    And yes, it's likely to result in a lower peak power, provided the bike was well tuned to start with.
  6. I know restricting exhaust produces more torque!

    ... but would obviously be bad for an engine designed to run with a certain outflow from the headers.

    FL, I can't give you a low-down on raw info, but you may want to research the development or theory behind expansion chambers in exhausts on 2-strokes. They have an incredible effect on the bike's power output, but whether it's specifically Kw or nM... or even limited to one or the other, I dunno.
  7. Where's my 'can of worms' smiley...

    If by 'restricting' you mean 'reducing the diameter of the exhaust to increase gas velocities and help the 'scavenging' process by maintaining momentum', and 'increasing the length of the exhaust runners to also help the kinetic scavenging' then yes. :)

    If by 'restricting' you mean 'insert a potato into the muffler to increase low-end power', then no. :)
  8. i could spend hours on an in depth reply, and cover all the attributes of the internal combustion engine, including its efficiencies and inefficiencies....but i CBF'd. the question is too broad.

    the mode by which you have posed your question, means that you have a "sorta ok" knowledge about how single and multiple cylinder engines work. so, the answer is, to pull out an encyclopedia, and study some physics. the answers you get here will be very simplistic, and backed (more or less) by the knowledge you already have.
    I studied internal combustion engines for 3 years, and still dont know it all.
  9. Great discussion topic, Falcon-Lord. Obviously it's broad, but that means the thread has some legs, rather than being something that can be answered in one or two posts.

    It seems as though there are a heap of variables, and perhaps trying to track them all down individually is too complex. I have a mental image of a diagram with 7 or 8 different dimensions represented as arrows, and a 'more power' along the top and 'more torque' along the bottom, to show the effect each has.

    But there's a question: are there things (other than sheer capacity) that don't involve a trade-off, and increase both power and torque?

    And another - someone here has repeatedly given a simple formula, something like 'torque = power x rpm' or something. Does that hold? If so, *every* dimension that increased torque would also increase power at the same engine speed, and vice versa. That doesn't seem to fit with the general understanding.
  10. The confusion comes around because "power" is used as colloquial for "top end power", and "torque" is used as colloquial for "low-end power".

    * Torque is a force. Like a wrench trying to turn a nut.
    * Power measures the speed at which energy is transferred - How quickly you can apply force. How fast you can undo a nut.
    * Power in this case literally is torque (force) multiplied by engine speed (velocity). P = F x V

    What accelerates a vehicle is power. What pushes against wind resistance is power. At low rpm, your engine is making power. At high rpm, your engine is also making power.

    In fact, if we rearrange the power equation (P = F x V)...
    'Acceleration force at the road' = 'power-at-the-wheels' / 'vehicle speed'.
    Where is torque? :-k

    At this point the "V8 torque is king!!" proponents chase me down with pitchforks and burning torches because they refuse to accept that their engines could be making power at all.

    Don't get me wrong - having a "torquey" engine (ie: one that makes power at low RPM without having to wring its neck) is great and does wonders for driveability. But it is power that the engine makes no matter what speed it is turning and it is power which does all the work.

    The torque curve tells you where and how the power is made. :)
  11. The R1 and the FZ1 use the same motor...but different power/torque ratings and at different revs.
    Same for the ZX-14 and 1400GTR.

    And you can by changing the valve timing (camshafts), usually increase the power but lower the torque and vice versa.
  12. :tantrum:
  13. GG... throw the word Peak in there a couple of times and I think Spo will relax.
  14. I will explain some of why I have asked the question (though it is pretty comprehensively answered) read anything by FLUX on the 675, and he waxes lyrical about the fantastic mid range power (Which I always read as meaning a Fat flat Torque curve). Now my view after riding the CBR600 was that I really had to make it squeal a little to get it to want to go, and that it seemed to me to have a fairly peaky narrow powerband. Yet with the Old R6 I road it was broad and easy to ride. So can you change the characteristics of a Donk without pulling it apart… And from what I have ready here, the answer is Not until they move pneumatic valves to commercial availability. So right now, the solution is rip the whole thing to bits and replace the timing Cams. So if you buy a bike expect it to be to much work to change those characteristics unless you are ready for a lot of work.
  15. This are a thread in desparate need of visual illustration. Here's some:


    You can see that the changes done in this tune-up increase the peak power and also smoothed out and increased the torque curve. You can also see that for this bike (a Bandit 1200) the torque curve is broad and relatively flat and while the power curve does have a peak it's not all that 'peaky' and has a pretty broad spread of power.

    By way of comparison, here's one for an R1:

  16. Just to throw something else in here as it's something that is kicking around in the back of my mind: Don't forget Compression, I think it works like Higher Compression gives you more "power" and Less compression gives you more "Torque"

    Now this is where I start making stuff up, if you've got one cylinder you have X compression, if you've got two cylinders you've got 2x X which gives you more "power" and so on. And you can change the Compression of an engine by the piston rings(?) I believe, which is why you can have two different engines, with the same number of cylinders from the same block produce different power and torque figures because of the slight differences in engine compression. And by this reasoning, you can "tune" an engine by the same method
  17. No. :)

    Higher compression improves the efficiency of combustion and will always* make for a bigger 'bang' (more force). More force per bang means more torque and consequentially MOAR POWAAAH. Across the whole range. Just like increasing displacement.

    * (you may sometimes reduce compression ratio so you can get way with running even more supercharger/turbocharger boost, to make even more power, but we'll ignore that for now)

    Compression ratio can be changed by replacing the pistons entirely, or changing the thickness of the head gasket (or shaving down the head sometimes).
  18. More air + more fuel = More power

    Or an other way of more power is Bangs per Second

    He he Power....... Oh sorry Sidetracked......

    Seen any stuff on Saarb's variable compression engine? Complex, but kind of cool :)
  19. That would be me, and yes, it holds.

    It's actually how dyno's compute the torque curve. You can generate a power graph for any engine, but unless you know the rpm's at some point on the power graph, then you cannot generate a torque curve.

    Torque is measured in Nm, or Newton-meters. What this means (1 Nm) is that if you have a lever off the crankshaft that was 1 meter long, then you have the equivalent of a force of 1N being applied to the end of that lever. 1N, for the layman's ease of visualising, is equivalent to the force required to hold 102g of weight against earth's gravity.

    So, when an engine makes, say, 70Nm of torque, it's like having a 7kg weight hanging off the end of a lever than is 1 meter long. Before you say to yourself: "That doesn't seem like much!", go find a broom, stick 7kg on it located 1m from the head, and then holding onto the head of the broom, try to rotate it so that you're holding the 7kg of weight (and the broomstick handle) horizontally. It really is quite substantial amount of rotational force (aka torque).

    So, that's what torque is. Torque is nothing though unless it's continually being applied in a circular fashion so make the engine crankshaft spin. If the crankshaft doesn't turn, then the engine isn't doing anything. Could have 1000Nm of torque, but unless it turns, it's doing nothing.

    Now we get to "power". If the crankshaft is turning, and that 70Nm of torque is being continually applied to make it turn, then the engine is now doing something, and through the gearbox and final transmission to the rear wheel, make the bike go forwards. The faster the engine turns, the more power it's going to make, 'cos we're applying that 70Nm of torque more and more quickly, and so now we're doing lots of work.

    Now engines don't have flat torque curves and straight line power curves, because of all the complexities of combustion, friction, flame-front speeds, and so on. The faster an engine spins, the flame-front of the combustion can't "keep up" with the piston speed, and so it exerts less "push" against the piston, therefore making less torque. Eventually the torque drops off so quickly that even adding more revs doesn't give any more power, and so the engine reaches its peak.

    When people refer to a "torquey" engine, what they really mean is an engine that generates a good amount of torque lower down in the rev range, which really means, it's make a good amount of power lower down in the rev range too. It's that power that is really making the bike move.

    When people refer to an engine as "peaky", that are really saying that the engine has a weak torque curve lower down in its rev range in comparison to higher up in its rev range, and so the engine has to be revved hard to get to where it makes its most torque, and also most of its power.

    Hope that clears it up.
  20. It should also be noted that gearing counts for an awful lot. I personally believe that quoting crankshaft torque figures is a completely meaningless exercise outside of the engineering design team. It only serves to confuse the average punter who has no real idea what it means.

    The reason is this. The crankshaft torque then gets modified by the primary drive, the selected gear, and the final drive (chain). It's the exact same principle to a winch. If you tie a rope to a car and try to pull it up a hill, you can't do it. The force that you're applying simply isn't enough to overcome the mass of the car. If you instead use a winch, you can move the car up the hill because the winch is converting your meagre amount of force (applied as torque on the spinning arm of the winch) into a large amount of force through gearing, and you can pull the car up the hill without much effort.

    So, just because one engine has 20Nm of crankshake torque, and another engine has 200Nm of crankshaft torque, that doesn't necessarily mean that the 200Nm engine is more tractable at making a vehicle move. It's actually the gearing that dictates that. Aside from the noise of doing so, so long as the 20Nm engine was spinning ten times faster than the 200Nm engine, you could not tell the difference between the two engines when riding the bike.

    To the average punter though, 200Nm sounds more impressive and so must be better, when really that may not be the case. It is actually upon this sole misunderstanding is why Harley Davidson only reports its torque figures for its engines. They are relying on the average guy to think "Big torque - MUST be good". *insert Tim the Toolman grunting here*