Interesting for those who are interested : (Thanks to,Moto-Italiano aka
Moto 1 )
For you rev heads " R1 Yamaha, it will out torque any production litre
bike you put it up against at any engine speed."
THE DYNO AND WHAT IT MEASURES
The dyno we use is not our own. It would be very nice to have one, but
for us it would merely be a very expensive toy. Dynobike, recently
relocated to Moorabin, in Melbourne's south east , is where we go to
test all our bikes. The dyno used by Dynobike is a Dynojet Acceleration
Dynomometer. Most people will know it as a rear wheel style dyno.
This type of dyno measures the acceleration of a big steel drum that the
rear wheel of the bike runs on. The acceleration is recorded by the data
acquisition component of the dyno's software. Given the inertia of the
drum is a known constant, it is relatively simple for the program to
calculate the Power absorbed by the drum at any time during the run.
To calculate the Torque from this we need a corresponding engine RPM
value. This is because Torque and Power are related by a simple
mathematical equation. It is, however, a relationship that many people
do not understand.
To put it simply, Torque is the amount of work done and Power is the
rate at which the work is done ( or the amount of work done during a
given time ). The equations for these calculations are as follows :
For the imperialists : Power = Torque X RPM / 5252 , where power is
horsepower, torque is foot-pounds.
This means, for the sharp eyed among you, that any dyno curves
displaying both torque and horsepower for the same measured run, in
imperial terms, will cross at 5,252 rpm.
For the metric people : Power = Torque X angular velocity , where power
is Watts, torque is Newton-metres and angular velocity is radians per
second.
At this point many of you may be lost, but this is the system I learnt
at university and makes far more sense to me than the imperial system (
which really does talk about a single horse pulling a load out of a mine
shaft ). Expanding on this, there is 2 X PI ( the number you use when
calculating the dimensions of a circle, or 3.142 roughly) radians in 360
degrees. Therefore, the conversion from RPM to radians per second = RPM
divided by 60, multiplied by 2 X PI. This works out at about 10 to 1. We
then divide the result by 1000 to achieve an answer in kilowatts.
Simple huh.
The purpose of explaining all this is to show that you cannot modify an
engine for torque as opposed to power. Many people confuse the two terms
in this way. An engine that makes lots of low rpm torque will usually be
called a "torquey" engine. One that makes lots of high rpm torque will
be called a "powerful" engine.
Digressing a little, it is also not true that a v-twin will produce more
torque at the bottom of the rev range than a 4 cylinder engine due only
to the configuration. Most 4 cylinder engines are tuned for lots of high
RPM torque, at the expense of low end. Because the twins don't rev so
hard ( as a general rule ) they are tuned for max torque at lower revs.
The length and shape of torque curves is getting much better for most
engine types as development progresses, though, regardless of
configuration. If you look at a dyno curve for an R1 Yamaha, it will out
torque any production litre bike you put it up against at any engine
speed.
The truth is, an engine of a given capacity will make a certain maximum
amount of torque at some point in its rev range. Where this maximum
occurs depends on the engine style and tune. The best example of this is
a comparison between 2 valve and 4 valve per cylinder Ducati 900 cc
engines ( 900SS and 916 ). These two engines make about the same maximum
amount of torque, roughly 65 ft-lb. This figure, incidentally, is
approximately 90 Nm, or about 100Nm per litre, which is pretty much a
given standard no matter what kind of engine it is. You just get to
choose the RPM at which you want it.
The 900SS will produce a rounded curve with a peak at around 6,000 RPM
(70hp) in fuel injected form, whereas the 916 will produce an almost
flat, gently climbing curve that extends all the way to 9,000 RPM (110
hp). At 9,000 RPM, the 900SS is making about 45 ft-lb (80 hp), and is
just about to hit its rev limiter. A carburetted 900SS has long since
packed up and gone home, due to its long inlet manifolds. At this speed
it makes about 30 ft-lb. Something like a ZX9-R will probably keep its
65 ft-lb curve going strong to 11,000 RPM, which is the reason Kawasaki
can extract around 130 rear wheel hp from them.
It is interesting to note at this point that an engine like the modern
Honda CB750, with its twin cams and 4 valves per cylinder, has an almost
identical torque (and consequentially power ) curve to a Ducati 750 SS,
which is a single cam, 2 valve per cylinder. The reason being they are
both designed to work up to around 7,000 RPM. A GSXR 750, designed to
work to 13,000 RPM, will make nearly twice as much power.
So what does all of this mean. To make more power, either you work at
increasing the amount of torque your engine produces in its given rev
range, or you increase the torque at the top end of the rev range.
There are two main ways to do this. Either improve the engine's
volumetric efficiency to trap more air inside the cylinder, or increase
the amount the trapped air is squeezed. There is actually a third way,
explored by restricted race class engineers the world over. This
involves minimizing power losses throughout the engine, and is usually a
very involved and time consuming process.
We try to improve the engine's volumetric efficiency without pulling it
apart. This is why our mods don't involve engine disassembly. The
reasons for this is that many customers are scared by the thought of
their bike being pulled apart, and that it is time consuming to do
correctly ( which is money consuming )
We are quite happy to pull engines apart should you wish. We just don't
do it if it's not necessary.
Another of the things I have learnt from the dyno is that you need to
understand what it is telling you. A major point is that the highest
power will come from an engine that is on the lean side mixture wise.
When I took my Guzzi Sport 1100 down to Duane Mitchell's ( Duane is Fuel
Injected Motorcycles, or FIM) to remap the fuel injection to suit the
mods I had made, I finished the day with a bike that ran so nicely it
was just wonderful. The sort of nice that puts a real smile on your face
weeks later, be it cruising around or pulling hard past 7,000 between
corners. The smile vanished though when I went to the dyno and found I
had lost 5 hp. We found the hp again, by leaning the full throttle
mixture out by about 7%. On the road, all was fine until I spent a day
in the hills working the engine hard in 4th and 5th gear. It was very
obviously flat at the top end. A flatness not obvious belting through
the gears around town, but a very real flatness when working the engine
hard. Relaying this info to Duane, I realised I was telling him
something he already knew.
On the basis of this info, my method of dyno tuning has changed
slightly. I now find the most horsepower I can, make a nice graph of
this power and then richen the mixture slightly to get the most
appropriate mixture for the end user : the owner.
This can cause some agro when an owner decides to check their 120 hp 996
is making 120 hp. It will most likely make 117 or so hp the way I hand
it over when finished. If I claim a power figure, however, I make damn
sure I have achieved it. ( It never ceases to amaze me that people get
stressed over 1 or 2 hp. If you can feel 1 or 2 hp then you're a very
talented person. )
In the real world though, we ride motorcycles, not dynos. The dyno is a
fantastic tool to use, but no more ( or less ).
At this point, it is most important to thank Steve and Dave at Dynobike
for all their help. Six years ago (in 1994) when I first met them they
were helpful enough to encourage me to learn more and were tolerant of
my many questions. The freedom they now allow me in the use of their
dyno is something you don't get very often with such an expensive piece
of equipment. Very much appreciated.
CDIHL
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