I never claimed otherwise. I did originally build and use braked dynos though and because of the use of load cells to measure torque (which have problems with hysteresis and temp stability) and analog digital conversion errors they are all but useless for reliable and repeatable backups giving the sort of errors you previously infered.
Plus in the real world the correct settings are set for dynamic conditions. At least on any race car and race bike when you open the throttle in any gear on any track it actually DOES accelerate.
Under aceleration things like fueling and ignition timing need to be a little different for optimum. A highly tuned two stroke or turbo bike for eg will always be safe with the correct advance while in an accelerating dynamic condition. With the revs held static you would possibly begin to get detonation and internal heat problems that do not occur on the track or the inertia dyno.
As an example, I really wouldnt have been able to run my own turbo/nitrous drag bike engine at certain rpms with full load for 1 minute! Or even for 5 secs. Because the fueling was correct for a rapidly accelerating engine. Holding the revs steady at say 7 thousand revs under load would allow it to develop full boost at this low figure where it wouldnt have had chance to spin up the big T4 that fast - the bike accelerates as fast as the olde worlde Rajay T04e did at least in low gears. In high gears it doesent matter because we are already up at the 10,000 rpm mark! Only time WOT can be used in low gears (1st, 2nd, partly third) is off boost due to huge lag. So the fueling allowed for this rather than being over rich on purpose for cooling and to allow 25lb boost. Run the correctly set up bike at say 7k under load at WOT and it will burn pistons as its too lean at that rpm for the amount of boost.
No they dont.
They time each and every drum revolution individually. They subtract one from the other and the result is the difference in time taken on that next revolution. Then they plot a point - They sample the engines RPM during the drums revolution and both the average engine rpm for that drums 360 degree cycle and the time taken for the drum revolution is sent as a data packet with a handshake (and checked) to the software. It can and does plot drum revolutions. In my software you can choose to display this every rpm or every whatever you choose rpm. But it grabs ALL the data and does so in real time. It can see the gear ratio changing as the run progresses. It can do accurate plots of twist and goes or automatics as some of my car dyno customers do daily.
Err crap! What can I say!!!
Yes and thats a GOOD thing at least for race vehicles!
Secondly an engine dyno has the annoying fact that they drive
Yes much the same as the car/bike itself does when you drive it. And that can also be useful in setting up fueling on a trailing throttle or when setting up fuel injection on various modern bikes to spit flames on overun only at high rpm consistently! :)
When the measured flywheel acceleration this
Its a big big problem. The ingines own internal and flywheel mass is massively too small for the result to mean anything! In the case of carbs all you can tell is that it gives a different "power" curve as you change the accelerator pump jet. Throw it away. Its a gimick for dummies.
but if they drive a steel drum , the energy in it is
Yes they are! The drums inertia is designed to match an average car or bike. What do you think happens in your car when you lift your foot off the throttle? Or isnt it designed to slow down with engine braking! My good where do you get all this crap?
Yes : better ones
In whose experience? Better ones use all kinds of emf devices and they dont wear and last indefinitely.
Well you are again wrong. Why am I not surprised!
1) Engine dynos can be and often are inertial dynos too. 2) An inertial engine dyno is just as simple as an inertial chassis dyno using the exact same technology...Inertia dynos are cheaper no matter engine or chassis. They are the ONLY dyno system that is truly totally repeatable, even simple ones. They are because of this better for seeing really small changes like different coils or changing plug gaps. As I said you can clearly see the power output drop even turning on the lights during a run. Repeatably at will. I have never found any way to make braked dynos get close to this ideal.
Real reason is that tuners are as lazy as the rest of us. And a chassis dyno offers almost as much capability and gives the chance to evaluate gearbox/diff/oil/torque converter/gear change system like air shifters, etc as well as just testing an engine alone.
Leon Moss told me he couldnt see the difference testing engines on his chassis dyno or on the fancy engine dyno. He knew more about tuning than anyone else I ever met and I have met a lot of them!
The hand held thing is almost pointless. The braked dyno is the good old bocsh that the rep tests and calibrates using his reps car by turning a screw? Is that the one? Well trust me, buy a dynojet inertial dyno and prepare to be amazed. The bosch dynos are great for setting up basic fuelling, and ignition mapping etc because they let you read gasses and hold the rpm steady. For real race back to back testing and ABSOLUTE accuraccy between runs the cheapo dynojet dyno or one of mine if I was still interested in doing it would be much better.
The only reason they claim 500 is because they can actually do any amount! The only limit is traction. Again, another reason that bosch dynos are inconsistent is the rollers! Miles too small diameter and anything with a pair of rollers trapping the tyre has all sorts of grip problems. I couldnt even test my brothers 400bhp ish nitrous car on a bosch dyno because the thing just shook and wheelspins all the time! So much so all the dust and crap was falling from the headlining! And we had me, and two mechanics sat in the boot with a ratchet strap over the roof.
I have seen 1500 bhp cars tested without issue on single drum 48 inch diameter dynojet rollers.
I agree some do. In the same way that some "tuners" sell all kinds of expensive stuff that glitters and doesent work. Thats not the dynos fault - thats just because they get used because they are cheaper to buy.
That is not something feasable if
Well actually it is feasable. But would you want to be the one that tried to hold some seriously leant on turbo bike at steady rpm? Mine? Because when it detonated itself to death I would then be able to explain it was your fault!