| Author | Message | ||
     Fullpower |
greetings to all. In consideration of the Dynojet chassis "dynomometer" i am under the impression that the device can only measure acceleration, that is torque, and then only in a dynamic sense, ie the change in rotational velocity of the weighted drum. in my analysis, this falls short of accurately measuring Brake Horsepower. I propose this thought experiment to illuminate: vehicle condition A where in we run a strong, free breathing, cammed up 1203cc sportster,making 90 rear wheel "Horsepower" at 6800 rpm on a dynojet 150. vehicle conditon B: we make 2 changes 1) remove the 42 pound stock sportster rear wheel assembley( yes, weigh one ourself) and replace with a carbon fiber marchesini weighing only 21 pounds complete with tire, and 2) we replace the sportsters flywheels with those from the lightning, weighing lets say 10 pounds less. now we have reduced our rotating mass by a very significant amount, possibly approaching 30% in total, and we run the volumetrically identical powerplant on the same dyno, and we find that this "new" setup has a much greater potential to speed up the dynojet drum. we now have a 105 "horsepower" so with the same compression ratio, cams, carburetor, ignition, and volumetric efficiency, in actuallity the same engine, but with LESS WEIGHT, the dynojet measures more horsepower. I postulate that the ability of the engine to do work has not changed, and therefore the dynojet DOES NOT ACTUALLY MEASURE HORSEPOWER. if someone can please shed some illumination on my musing i stand ready to assimilate. thank you, dean h ravin | ||
| Wyckedflesh |
And if you take that sportster with those changes you will notice that if also runs the quarter faster. It is where the addage "7lbs=1hp" comes from. Also the Flywheel change will have the most dramatic effect on the horsepower reading. The change in wheel weight won't have as much effect. I beleive it was Sportrider that did a similar test on one of their bikes. They were setting it up for a race season and showing the effects of weight and the relationship to power. Going from a stock wheel to one of the Marchesini wheels netted them something like 1-2hp on the dyno but like 1 second on the dragstrip. Also the weight of the wheel is concidered part of the "driveline loss of power" when figuring in the difference between Rear wheel HP and Crank HP. | ||
| Jeffb |
You are correct, but bang for the buck it is the best option. You can also cut down and lighten your transmission, clutch, drive sprockets and any other rotating mass. It makes more HP and goes faster. Measuring engine brake HP is possible (with a dyno hooked directly to the sprocket shaft), but if you want to know rear wheel HP on your bike compared to everyone else out there the Dynojet is perfectly acceptable. | ||
| M1combat |
Yeah, it measures RWHP, but will need to be modified by a power to weight ratio to have any real meaning... | ||
| Fullpower |
to restate my earlier observation; the term RWHP refers to the rate of acceleration of a weighted drum, and should not be confused with the long recognized concept of "Brake Horsepower" where one is actually refering to the rate of work being done. again, if i hook my 500 horsepower peterbilt up to a loaded bellydump trailer, and go climb a 7% grade, blowing black smoke and maintaining a steady 35 miles per hour, i am making 500 horsepower, and there is no acceleration. in this example, at the governed speed of 2100 rpm, my bellowing 500 horsepower caterpillar diesel would read exactly zero horsepower on a dynojet chassis dynomometer. my point is the dynojet while being a useful tool to make comparisons, DOES NOT measure HORSEPOWER. to observe the lightening of the rotational mass of a motorcycle to increase its horsepower output is fallacious. yes it can certainly accelerate faster, and post a higher set of numbers on a dynojet, but it can not burn more fuel, nor can it burn it more efficiently and produce more shaft horepower, just by the magic of reducing the weight of its rotating assemblies. yes it CAN spool up faster, but it CANNOT do more work. | ||
| M1combat |
Agreed, but what exactly is the definition of RWHP. It's a measurement of how much power the total package can put out. Not how much acceleration the bike will be capable of, but how much acceleration the bike can impart to a weighted drum. I think that as long as the resistance imparted to the drum is the same, then those figures can be used compared to each other. Basically, when kept to an Apples to Apples comparison, the number means something. I agree though, it doesn't exactly measure brake HP, but RWHP. | ||
| Ceejay |
HP is actually measured in kilowatt/hrs, which is energy, the amount of energy it takes to do a measured amount of work. So fullpower is right. us two wheeled powerjunkies have decided that it is how all gas powered machines should be measured, when for the most part we can never actually use it because it is in an unstreetable part of the powerband | ||
| Jeffb |
Fullpower, you are right and no one is disagreeing with you. The dynojets calculate HP using acceleration and engine rpm. So what? Buells are not stationary power plants putting out a constant power at a constant RPM. We feel acceleration when we ride our bikes. This acceleration is a result of the mass of our vehicle, frictional losses, rotational inertia and the crank HP. We could add a scale to weigh our bikes before we dyno them so we could compare accelerations on the dynojets, but there is already someone doing that on that dyno drag truck thing. (never mind we should "mass" the bikes not "weigh" them) Are you on a mission to redefine how the motorcycle and aftermarket auto industry compare HP? | ||
| Reepicheep |
You make a good point about the amount of "voodoo" involved in current RWHP statistics. I also get frustrated when people get hung up on peak HP, as it is just about worthless, as opposed to the HP versus RPM curve, which is what really matters. I have fun describing peak horsepower in a number of different ways to make points to people... "It's a measure of what your bike is doing at the moment you can no longer do it anymore." "It's a measure of what your bike does when ridden in a manner you never ride it". Though twin owners make just as silly assertions about torque, which really does not mean a thing. Horsepower *is* the right measure, but it needs to be plotted versus street speed, for the speed range you will use the bike at. It would look like a sawtooth, and you should pay more attention to the low spots then the high spots. IMHO. Good topic. | ||
| Fullpower |
Jeff b no i am not on a mission. just A) attempting to shed some illumination on the often used but nebulously defined concept of "RWHP" B) pointing out the arbitrary nature of the measurement, while still admitting it's utility for making comparisons between vehicles, and assessing the effects of modifications to a given platform. C)advancing, by way of roundtable discussion that one 'RWHP' does NOT equal 746 watts, nor does one RWHP= 33,000 lbs ft/second. but rather it is an arbitrarily defined unit of acceleration on a proprietary weighted drum. and finally D)hoping that someone here will admit that the term "rwhp" when bandied about for bragging rights just means they are quite likely spinning a small crankshaft really fast. discussion?? | ||
| Fullpower |
wycked point taken and noted about the simple change to a lighter wheel netting one full second faster quarter mile time, but please note the nearly negligible dyno change of 1 or 2 rwhp. i have a friend who has a hot rod sporty, and claims to have installed the flywheels from an S1 lightning and gained ten RWHP. i freely admit that motors gonna run better, rev quicker, and the bike will certainly accelerate faster. BUT THAT IS NOT WHAT HORSEPOWER IS. the dynojet can measure the potential for acceleration of a given wheel weight. the dyno sees and measures torque. from this data it can calculate horsepower at each designated rpm. but this is NOT HORSEPOWER. example take 2 identical R1's vehicle one is run on the dynojet and lets say it makes 160 RWHP, then vehicle two in all ways identical EXCEPT we put a 42 pound sportster rear wheel assembley on it. we have just added lets suppose 19 pounds to the rotational momentum of the rear wheel. will the dynojet calculate the same RWHP? no, we will find a lower number of RWHP evident solely because we added weight. the R1 engines will both be working just as hard, the two fuel injection systems will both be pissing at the same rate, they will be making identical shaft horsepower, but the RWHP will be different. | ||
| Reepicheep |
I was with you up to D. The bikes posting big HP numbers may be spinning small crankshafts really fast, but they are also typically putting out a ton of watts. The rotating mass difference is measurable. Do runs in first and fifth and use the gear ratios versus the difference in results. And I bet the mass of the Dyno drum is so much higher then the rotating mass of the bike, the effect is moderated significantly. | ||
| Fullpower |
so in theory then, with a massive drum, one would not make much if any RWHP change with say a six pound reduction in clutch hub, and ten pound reduction in flywheel weights? | ||
| Wyckedflesh |
Horsepower is the measure of Torque times RPM divided by a constant. Torque is the measure of work. So if you take your example of the dumptruck on the grade, measuring horsepower is useless as that isn't going to tell you anything. What your measuring is purely torque, or how much work the engine is doing. Rolling drum dyno measures the amount of work the engine puts out in order to move that drum. If you go to a lighter rear wheel, then the engine has to work less to spin that wheel as well as the drum. Now the engine has left over work energy that it uses to spin the drum. Since in this case the machine measures how fast the engine can spin that drum up to speed based on the RPM of the engine it can tell how much energy is being spent to spin that drum. Since more of the energy is going into the drum and not the wheel it will read higher. The other thing the roling drum dyno does is measure how easily the engine keeps spinning that wheel as it runs up through the RPM range. After the engine passes its peak torque the dyno measures the change in the drumspeed. It can tell when the motor starts laboring again to keep the drum rolling, that coincides with the horsepower falling. How does this apply to us? Well as you said a dyno is simply a tuning tool. In the hands of a good operator the dyno can tell you if the changes you made are beneficial to your goals. If your lightened flywheels are a help or not. If you looked at the dynograph and compared the lightwieght to the heavy weight flywheels you would see the lightweight has a lower rpm peak for the torque and a higher rpm peak for the horsepower. The heavier flywheels will peak the torque higher in the revrange put peak the horsepower lower in the rev range. So basically the actual numbers that are printed are just for bragging rights. Its the graph that speaks more then the actual numbers. A dragracer will be more interested in the upper part of the graph where the horsepower is peaking because he is at WOT, a cruiser will want to look at the lower part of the graph where the torque range is because he is barely using the throttle. An all arounder will want to look in the middle where the two part for their useable power because he is up and down through the middle of the range constantly. Ok to address this statement: to restate my earlier observation; the term RWHP refers to the rate of acceleration of a weighted drum Only if that is the type of Dyno that is used. It is possible to set up a Brake Dyno for rearwheel measurements. They aren't generally used as much anymore because of the sheer size of the machinery involved. Its easier to set up a brake dyno for crank measurements but that doesn't make a real world measurement either because of the losses through tire/wheel weight and the parasitic losses of the final drive method (chain or belt). It also doesn't take into effect final drive ratio in relation to the gearing between the output sproket/pulley and the wheel sprocket/pulley. Gear it too high and the engine bogs down, too low and the engine tops out to fast. Its why Crank and Rear Wheel HPs are different with the Crank HP being higher. Rearwheel horsepower is a great measure of the amount of power that is being put down by the driving tire. Its the amount of power being aplied to the road. If you use a lighter wheel then more power is transmitted to the road as less power is used to spin up and maintain the spin of the wheel. | ||
| Wyckedflesh |
one would not make much if any RWHP change with say a six pound reduction in clutch hub, and ten pound reduction in flywheel weights? Depends on what you mean by much of a change. You will have less parasitic loss through the drivetrain with the lighter clutch hub. This in turn frees up horsepower to the dyno drum. See my long post above with regards to the flywheel weights. | ||
| Wyckedflesh |
Oh and YES I agree EXCELLENT topic  I would also like to note that its things like this that I beleive Aaron from NRHS mentioned when he said it was easy for Dyno operators to fudge the testing. | ||
| Blake |
"HP is actually measured in kilowatt/hrs, which is energy, the amount of energy it takes to do a measured amount of work." Try again on that. You have the idea, but are a bit confused on terms. Hint... "HP" is a measure of power as are kilowatts. | ||
| Fullpower |
all good points gentlemen, i am enjoying the discussion immensely. i am in receipt of a technoresearch dongle and disc combination, but alas my buell is not here at my computer desk.... so many thanks to all for helping pass the time..... later, dean h ravin | ||
| Fullpower |
as Blake hinted at HP= 33,000 lbs ft/sec | ||
| Fullpower |
no, that seems to high a number, help somebody? | ||
| Wyckedflesh |
The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. We are also reminded of him every day when we talk about 60-watt light bulbs. The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner! What horsepower means is this: In Watt's judgement, one horse can do 33,000 foot-pounds of work every minute. So, imagine a horse raising coal out of a coal mine as shown above. A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. You can make up whatever combination of feet and pounds you like. As long as the product is 33,000 foot-pounds in one minute, you have a horsepower. You can probably imagine that you would not want to load 33,000 pounds of coal in the bucket and ask the horse to move it 1 foot in a minute because the horse couldn't budge that big a load. You can probably also imagine that you would not want to put 1 pound of coal in the bucket and ask the horse to run 33,000 feet in one minute, since that translates into 375 miles per hour and horses can't run that fast. However, if you have read How a Block and Tackle Works, you know that with a block and tackle you can easily trade perceived weight for distance using an arrangement of pulleys. So you could create a block and tackle system that puts a comfortable amount of weight on the horse at a comfortable speed no matter how much weight is actually in the bucket. Horsepower can be converted into other units as well. For example: 1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts. 1 horsepower (over the course of an hour) is equivalent to 2,545 BTU (British thermal units). If you took that 746 watts and ran it through an electric heater for an hour, it would produce 2,545 BTU (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F). One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient. | ||
| Fullpower |
thanks wycked. i love this place. | ||
| Wyckedflesh |
 Btw, I thought of something else WRT your buddies Sporty. I have a difficult time believing that he didn't refresh the rings and hone the cylinders while he had the cases apart to install the Flywheel from the S1...that alone could have added a HP or 2 | ||
| Reepicheep |
Don't stop there! Power, as measured in watts, is equal to voltage times current. More of either and you get a linear increase in (horse)power. Thats why a 15 amp fuse on your Motorcycle (12 volts) will basically run a headlight (12v * 15amp = 180 watts) but a 15 amp fuse in your house will run an entire floor (120v * 15 amp = 1800 watts). Therefore, powers is also equal to Voltage Squared / Resistance. And equal to Current Squared Times Resistance. Power == heat, except when it does not. A 500 watt heater is putting out 500 watts of heat (duh). A 500 watt incandenscent bulb is putting out probably 300 watts of heat, and 200 "watts" of light. A 500 watt flourescent bulb (which creates more light and less wasted heat then a filament bulb) may put out 50 watts of heat, and 450 "watts" of light. A 500 watt motor may be doing 400 "watts" worth of work (horsepower), and putting out 100 watts of heat. Whee! | ||
| Wyckedflesh |
Yeah but that is getting beyond our discussion of the differences between a Dynojet rolling drum Dyno and a Brake Dyno As well as the difference between RWP and BHP | ||
| Reepicheep |
Arrghhh... can't help myself..... The astute reader will notice that you can transmit X amount of power at a given voltage and a given current. Say 100 volts and 100 amps for 10000 watts transmitted. However, the power being "lost" in transmission down the power line is simply Current Squared times Resistance of the wire. More current, more transmission losses (and more heat). Less current, less transmission losses (and less heat). So what if we changed our 100v and 100amps to be 10000 volts, and 1 amp? Same amount of power is transmitted, but our transmission losses go down by a factor of 100, as our current transferred went down by a factor of 100. That means our transmitting wire goes from a huge honking fist sized wire, down to a skinny little line of copper. Thats why if you go from the US to, say, Germany, where they use 220v instead of 110 volt, you will see the cords on things like hairdryers and power drills are these skinny little phone cord looking things, instead of the big fat wires we are used to. And more importantly, thats why big voltage transmission lines (cue Court) are running at like 30,000 volts. They want to transmit boatloads of power with little current being moved (and therefore little lost power). Further (acck. somebody take the computer), that is why Nikola Tesla and Westinghouse kicked Thomas Edisons ••• when it came time to run power to the planet. Edison was all DC, one voltage, high losses. Tesla / Westinghouse were all AC, which with easy to manufacturer transformers, could be easily and efficiently stepped up to high voltages for transmission, then stepped back down to low voltage at your doorstep for home use. Of course Tesla, being a great scientist, died penniless feeding pigeons, and George Westinghouse, being a great business man, had more money then could be spent in 10 lifetimes. Hrrrmph... Back on topic... Ummmm... So westinghouse, had he lived to 1996, would surely have bought a Buell? Now stop baiting me with these great threads. I am *way* behind on work. :/ | ||
| Blake |
Some clarifications are in order. There are two ways and two locations typically used to measure vehicle or engine performance. Two ways: 1. Inertial/accelerative power 2. Brake power Two locations: 1. Rear wheel 2. Crankshaft Any method that utilized a change in inertial drum speed over time to measure power is inertial/accelerative and will always reflect power losses due to energy storage in any drivetrain rotational components (flywheels, gears, rear wheel/tire assy...) A brake dynamometer by virtue of a brake, holds the test vehicle's engine at a constant speed even under full power and measures the torque or power required to do so depending on the type of brake employed. That brake torque or power is then translated to the reported "brake HP" figure. The brake dynamometer method sees zero losses due to energy storage in rotating drive train components. The brake HP of an engine or vehicle will ALWAYS exceed it inertially deduced HP. Brake dynos use either a mechanical brake and a load cell to measure the braking force (torque) required to maintain constant engine speed, or as is more commmon these days an eddy current (electrical) brake. The edddy current brake may still utilize a load cell for direct measurement of the resisting torque or may be calibrated to report actual power based upon the voltage and amperage of the current being generated in the brake. Dynamometers exist in various configurations where either brake or inertial methods may be used at either the crankshaft or the rear wheel. What is typical is HP measured inertially (through acceleration of a known rotating mass) at the rear wheel. Thus any energy that is being imparted and thus stored in the engine's flywheel or other flywheel-like drivetrain components including the rear wheel during acceleration will not be recognized by an inertial/accelerative dynamometer. For the drag strip the inertial dyno is best for replicating real world performance. For land speed racing where engine speeds become near constant, the brake dyno method will more accurately reflect real world conditions. Hope that makes sense. A Dynajet 250 provides both the typical inertial and the less common brake dynamometer power measurement modes. | ||
| Oldguy |
Don't have all of my magazines here as they are in storage for an upcoming move. I do recall that one of the cycle mags installed a dyno a few years back and warned that their HP numbers would be lower than other mags as they would be using an eddy current style dyno. Most of the Dynojet dynos are of the accelerometer style as these are smaller and less expensive/complex. Remember that the old Clayton dynos used water brakes which required a big hole in the floor for the tank/drum assembly and the engine was held at speed while the operator adjusted the water level/drag to take a reading at one RPM and then had to repeat for the next RPM. Motorcycles, many of which are/were air cooled, would not respond well to being held under load while readings were taken. Another reason the accelerometer style dyno is used. Hey, Blake. Very informative post but there aren't many numbers. You feeling okay? Glenn | ||
| Blake |
Numbers are to difficult to type quickly. | ||
| Opto |
At the end of the day, the dyno measures how fast a particular motorcycle's back wheel will accelerate the dyno's drum. For a particular bike any changes in performance can be noted, and for different bikes the acceleration will be approx in proportion to measured "RWHP" divided by weight (including rider/s). | ||
| Pammy |
Some Dyno mfg's use different mathimatical equations to calculate HP. There is the proven calculations..then weight, air density, elevation, etc...are calculated in. Then the operator adds other variables, such as the riders weight and amount of pressure on the rear wheel when the bike is tied down(same difference in rider weight)There are many variables which will amount to a change on the Dyno. As a performance specialist, you try to eliminate as many as possible. For example, on our dyno, we use the same rider for the beginning run as the final run. We don't tie down the back of the bike at all(how do you measure the exact tq on a tie down strap every time?) The air pressure is checked throughout the runs. Temps are checks and noted, air is cleared, etc, etc... The idea with using a dynomometer is to eliminate as many variables as you can. The dyno is a comparative tool and should be regarded as such. We start with one HP and end up with another. Changes in parasitic loss are noted and taken into account. It's a tool, much like the flow bench we use...now THAT's really interesting! | ||
| Blake |
When you get the new shop built, please post a before and after pictorial. With you of course doing the official Carrol Merryl for the camera. |
