TripleZee Cycles

BECAUSE PEOPLE ASK ME WHY THEIR BIKE MAKES MORE POWER ON A DYNOJET.... WELL IT DOESNT, ITS THE SAME BUT DIFFERENT, SORT OF… 
IT'S THE WAY IT IS CALCULATED and DISPLAYED THAT IS DIFFERENT
 
      Lets have a look

 

SO WHICH IS RIGHT??
They are all right and all wrong to varying degrees.
I know I am biased BUT the in order of MOST RIGHT to MOST WRONG

 

SIMPLE REASONING
There are less variables, errors and losses introduced with the Brake.
The Brake Dyno essentially has One Variable to deal with
        Transmission Loss

An Inertia Dyno has all these "Variables" to contend with
        Inertia value of the drum (I know that this is fixed but it introduces other variables further down the track)
        Inertia value of the bike
        Transmission Loss
        Inertia Correction Factor
        Transmission Loss Correction factor
        Variable Acceleration Rates due to fixed Inertia of Rear Drum

Although the Mass of the rear drum is fixed and known, depending on the power of the bike being tested the acceleration rate of the drum varies.
While the mathematics can cope with varying acceleration, it can’t cope with how a particular engine responds to different rates of acceleration.
Basically the tuning requirements are different and most EFI systems have correction factors built in to compensate for different acceleration rates. Sometimes these correction factors are linked to what gear you are in as well.
Its pretty obvious that a Hayabusa or ZX14 is going to respond differently between say 2nd gear and top gear.

IRunning a bike in different gears on an Inertia Dyno can give different results

Because of the Inertia effects you can get different results by running in different gears. Engine HP and Torque are independant of what gear you are in, apart from some of the large Japanese motorcycles which have power limiting applied to the lower gears. Basically the bikes rotational inertia effects increase in the lower gears, the net result is less apparent HP. This effect varies. The bigger and heavier the rear wheel assembly is the bigger the difference.

Something to be aware of as a lot of people spend too much time comparing HP figures.

And if you dont think your bike is running that much better after all that tuning, but the graphs show a reasonable increase, it wouldnt be the first time an unscrupolous operator has done the base run in a lower gear and then the finals in a higher gear, and then claimed the credit for the increase in apparent power.

Many bikes have to be tested in low gears because they just dont produce enough rear wheel torque to spin the 1000lb roller.

On the other hand torque monsters produce so much rear wheel torque the inertia run is over in a few seconds even in top gear. No way can you get good tuning information from such a short run.
Its all just too much Damn Hard to work it all out and get a meaningful answer.
So for all practical intents and purposes the "figures" you get are a good guess at best.

Having said all that

Provided the operator is consistent, and knows what he is doing he should be able to do a reasonable job.

All the better if you understand and can interpret your graphs and dont get too hung up by numbers.

Using a Brake dyno you get Rear Wheel HorsePower.
RWHP that’s it, Doesn’t change because you remove the alternator rotor or put a light weight rear wheel on. or change gear.

Crankshaft HP minus Transmission Loss.

Simple, Straightforward, Accurate

Bigger HP reading on your graph?

Using a Brake Dyno reduce transmission losses or tweak the engine will result in more RWHP

Using an Inertia Dyno reduce transmission losses, tweak the engine, reduce Inertia losses by lightening up components such as the rear wheel (easy hp), clutch assy, alternator rotor, crankshaft, chains and sprockets will all result in more RWHP

A Brake Dyno gives a much more Accurate and Consistent Representation of Engine Horsepower

An Inertia Dyno works well but there are too many external (to the engine) factors affecting the output.

A Brake Dyno actually works better as an Inertia Dyno than an Inertia Dyno does!!!!!

A Brake Dyno controls drum acceleration during a sweep test, more "real world" than an uncontrolled inertia sweep test.

(A 250i in theory can do this but in practice the brake gets overloaded due to the inertia of the rear drum)

Some people say accuracy doesnt matter as long as you use the same Dyno.

Bit like every builder having his own definition of a metre.

As long as you used the same guy all the time you would be right.

Makes sense to somebody I suppose

Now you know why there is BHP, RWHP, EHP, and some others but there isnt IHP (Inertia HorsePower)
Why manufacturers use Brake Dynos, why race teams use Brake Dynos, why the EPA uses Brakes. A lot of these people also use Inertia dynos, BUT they are NOT used as the “primary tuning device”

Why has DynoJet added a Brake to their Inertia Dyno?
The primary reason is to enable Auto Tuning of Power Commanders via Tune-Link
Unfortunately it will be a while before they bring out a dedicated Brake Dyno. No-one is going to like putting their bike on the latest DJ Brake Dyno and "losing" 20hp compared to the old Inertia based DJ!!
And that is why when doing a "Power Run" it is done using the Inertia Dyno. Looks better on the graph!!
The Inertia Dyno could be “corrected” with input from the optional Torque Cell, but the resulting HP/Torque output would be lower making for grumpy customers so they leave it as is.

Dont get me wrong, the DJ is a good Inertia Dyno But it is an Inertia Dyno and no amount of fiddling, adding brakes, faster computer, etc will get around the fact that there is a near on a 1000lbs of Inertia inducing drum assembly connected to the rear wheel.
A half decent Brake Dyno can do everything an Inertia Dyno can do but even the best Inertia Dyno cant do what a half decent Brake Dyno can do.
Brake Dynos are also subject to Inertia effects, but they are minimal in comparison to an Inertia Dyno.

Why does DynoJet sell so many Dyno's then?

Why do McDonalds sell so many burgers?
Why does Microsoft sell so many copies of Windows, considering Linux is "free" ?
You figure it out. But give Mark Dobeck his due, he saw a gap in the market, took the opportunity and did a great job marketing and selling his Dynos

A BIT OF HISTORY

Hot Rod Article re Mark Dobeck and Dynojet

*******Dynojet's final number-fudge was arbitrarily based on a number from the most powerful road-going motorcycle of the time, the '85 1,200cc Yamaha VMax. The VMax had 145 advertised factory horsepower, which was far above the raw 90hp number spit out by the formula. Meanwhile, existing aftermarket torque-cell engine dynamometers delivered numbers that clustered around 120. Always a pragmatist, Dobeck finally ordered his Chief Engineer to doctor the math so that the Dynojet 100 measured 120 hp for a stock VMax. And that was that: For once and forever, the power of everything else in the world would be relative to the '85 Yamaha VMax and a fudged imaginary number. Dobeck's engineering staff was dismayed by the decision******

Why did Dynojet do it this way?
Simple Marketing. It looks better. If some guy put his magic gizmo on a Sportster and got 90hp and another guy got 100hp with his gizmo who do you think will sell the most?

And before someone carries on about the 250i being a Brake Dyno, It ISNT. Its a Hybrid Dyno, an Inertia Dyno with a brake attached. (and thats from the big cheese at DynoJet)
There are quite a few Hybrid Dynos around, eg water brake + eddy current brake, water+inertia, etc

When All Said and Done

Whatever dyno you have or get your bike put on, its a tool, and like any tool, how good it is has a lot to do with the nut driving it.

But the Best Combination will always be a Good Nut Driving Good Tools

cheers

   Technical Questions/ Product Inquiry?