Thoughts on Dynos.

[koko64]

Reading a book on tuning by Bill Rook and some recent conversation with Brad Black has had me thinking.
Dynos.
Being instruments/tools of measurement, what are some of the issues and pitfalls around their use, and how to best use these expensive contraptions?
Been using a local dyno a fair bit lately and here are some things to consider.

Does the dyno have an EGA to give you guidance re jetting?
Does it have a built in, automatic weather station linked to the computer to calculate correction factors for the weather? Or, does the dyno operator have to make those inputs manually? How tamper proof is the process?

Does the dyno operator test your bike at the same operating temperature when comparing settings or tuning mods? Does the operator warm your bike up properly before test runs?
I have seen the hp increase as the bike warmed up properly, then taper off as the bike and room heat right up. I was concerned that my bike was thrashed without being at its best operating temp.
If the bike's motor is not at the correct operating temp then the hp readings may not be accurate. How long was the bike sitting there cooling off before it was lashed to the dyno?


Was the throttle opened the same way on each comparison run? All my testing has been by the same guy except for once and I noticed how the power came on was different. When testing FCR carbs, the older operator (the normal guy I use), opened the throttle quickly to about 3000 rpm then snapped it open, the young fella (of the injection era) pinned the throttle from idle

Is the dyno room temperature controlled?
I have seen the heater left on in the room affecting the correction factor the weather station and computer detected and selected. The dyno operator said that he was surprised the bike made as much power as it did with the high heat and humidity in the dyno room. The guy opened the door letting the heat/humidity out and for the next run the correction factor dropped.

What model and make dyno is it? How well maintained is it?
There are generous and stingy dynos around. Some earlier models of the same company are more generous than later versions. Even the same model and make can differ.
A dyno near me that I haven't used is known give a handy horsepower increase. It is operated by a master tuner and good guy, but is probably thrashed heavily, so I'm guessing it is well worn in.
 
The dyno I use is set to STD hp figures which reads higher than SAE hp which I have grown up with. Make sure you aren't comparing apples and oranges.

Patrick Burns has a link in his "FCR Tuning Procedures" advising a Formula 400 racer regarding a whole bunch of dyno tuning tips. Really valuable stuff.
Brad Black has some good articles regarding dyno tuning on his bikeboy.org site.

Dynos are such useful devices allowing you to check your work which frees you from having to be committed to untested concepts.

What matters, is that the dyno being used is operated with a consistent procedure that removes all the outside influences that could contaminate your data.

Is anyone in the States running courses on dyno operation, beyond the instructions given to buyers of dynos? If there is it would be a good thing.
I for one would be interested.

[motoxmann]

the biggest thing about dynos is people get way too caught up in the actual numbers. 90% of the time, the numbers really dont matter and don't mean squat, because every dyno will give different readings, and even identical dynos will be set up differently and operated differently. dyno should not be used to determine how fast your bike is; dynos are specifically designed as a tool for tuning, with the purpose of getting a reading as close to realistic road conditions as possible, making changes to the setup, and comparing the data from that to the data of before the changes.

as for operation, there are different methods of operating the dyno as well. ie: starting the run at idle vs starting the run at 3k vs starting the run at 5k. different starting points will affect the later parts of the run due to heat differences that can't be replicated vs actual street use. it's good to start lower than normal, but the operator needs to know the intent is for tuning that lower rpm, and not to rev all the way to redline because all that higher rpm data is useless.
often times what I used to do (I tune cars) is take the car on the street and record temps of various things, and time approx acceleration. then when on the dyno I would get the car to a point where the temps of those previously recorded on the street are as close as possible when beginning the dyno run, and timing the acceleration rate on the dyno and finding the best setting to replicate street acceleration. because using different loads that alter the rate of acceleration will give different readings for power and AF and other things.

I could go on for days talking about everything dyno related based on my personal theory, common theory, common experience, and personal experience. fact is though, there's a million ways to do things on a dyno, some are right some are wrong, sometimes the wrong way is actually the right way under specific conditions or for specific purposes. but the biggest thing is that the numbers don't mean jack individually; the main concpet is to use the numbers for before/after comparisons

[motoxmann]

the best advice I can give to anyone who wants to learn about dyno stuff:
don't try to find the 1 or 2 best and most recommended "lesson" on dynos; read as many different "lessons" as possible from as many varying sources as possible and combine ALL of that knowledge to form your own theories and common knowledge, knowing that there will be mass amounts of contradiction and knowing how to sort it out and when each differing thing should apply to individual circumstances. I personally still learn something new with almost every vehicle I tune whether it be on the street or the dyno

[Speeddog]

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[koko64]

Thanks mm.
Very true. Its the trend in data or change in power characteristic to watch for more than just a particular number.
I may pm you from time to time if that's ok.

[Speeddog]

Additionally...

Look at the data with a critical eye.

In late '03, I installed a PCIII on my S4.
That PCIII could only alter the fueling.

Took it to the local dyno, had it 'dyno tuned'.

The 'after' power curve was higher everywhere than the 'before' curve.
Not a lot, but 2-3 HP higher everywhere.

Including the 3 areas where the 'before' and 'after' A/F ratio curves crossed.


Made me a bit skeptical.

[motoxmann]

I may pm you from time to time if that's ok.

yeah thats fine

[BozcoRob]

 

[ungeheuer]