[xBhp Universal Thread]: principles of dyno run

[kachhhing]

Guys , i happened to read a very interesting article on dyno run in an old magazine, thought would share it here
the following is verbatim from the magazine.
no questions should be directed to me, cuz i would have no clue to answer them :-)
but i suppose we all can share a bit of knowledge and interact.

read on .....

There are several different makes of dyno but, at the most basic level, they all work in a similar way. a bike is attatched to the dyno in such a way that it cant move. while the driving wheel acts on a heavy, metal roller.

the dyno perator puts the bike in gear and rides just as he would on the road. the difference is , rather than pushing the bike forwards, the rear wheel simply spins the metal roller - and this is how the power and torque figures are calculated.

there are different types of tests with varying names like "roll on" , "fast acceleration" , "step testing" and load testing" and each has a specific purpose. the easiest and the most repeatable of these is the roll on test, which is he one printed in magazines and nearly always done first. to do this the bike is generally put in 4th gear - altough the actual gear doesnt matter. if the gear is too short, there will be lots of wheel spin and it will appear that power has ben lost. equally, if the gear is too tall, the engine will take a long time to spin the roller, getting hot in the process and in extreme cases , wont rev out completely.

once in gear, the revs are allowed to drop, before the operator quickly (but smoothly) opens the throttle to the stop. at the same time, the dyno starts to record - as the engine revs pick up and the wheel accelerates the metal roller. when the engine hits the rev limiter, the operator shuts the throttle and stops the recording. the dyno now has a record of the engine revs and the rate at which the roller was accelerated.

the process will be repeated several times until the power output reaches a consistent level.

WHAT ARE POWER AND TORQUE :-

power and torque are words that describe "work" and the " rate of doing work"
practical example :- how heavy was the box you carried upstairs and how long did it take ?
some one who is able to cary a heavier box is able to do more work ( more torque)
meanwhile some one who is able to carry the same box (that u carried) , but move faster is clearly more powerful ( has more horse power )

while the bike on dyno hasnt carried anything upstairs, it has been forced to spin the roller, so we have asked it to do some work. the dyno records how fast the drum is spinning, so its possible to calculate how much work is done as well as the rate at which its done ( torque and power )

to put this in terms we can understand, its normal for a dyno to also record or calculate , engine RPM. having done so, we can see how much power the engine makes at a certain rev point (rather than road speed) and that means we get easily comparable results, even if we change the gearing.

UNITS AND COMPENSATION

power :- kilowatts (kW) and pferdestarke (PS)

torque :- Newton - meters ( Nm) , kilogramme meters (kg-m).

If environmental conditions change, the engines power will change too. to get around this several methods of correction have been constructed.
they take into account atmospheric condtions when the dyno is in use, and this data is used to estimate how much power the engine would have made had conditions been ideal.

the most commonly used correction is DIN, and you will often see this followed by "c/f" or correction factor and a number. this is a ration that shows you how much the figures have been adjusted.

for instance :-

C/F : 1:00 means no correction at all
C/F : 1:01 means the values you are looking at are 1% higher than the values that were actually recorded
C/F : 0.99 means 1% lower.

for this reason most dyno rooms have cooling fans in front of the bike.
also the rooms are designed in such a way that air flow into the room is the same as the push of the fan.
the direction of air should be towards the rediator, so it helps to cool.
but if directed upwards, it supplies the engine with clean air

[Aryan]

Universal Thread Approved.

Please do mention the source of the article as well.

Thanks.