Phone

(603)

974-2183

    What are the differences in dynos?

and

What about Ours?

There are two main types of dynos.  There are brake style dynos and inertia dynos.  Brake dynos use exactly what you think they would use.  A brake.  The simplest type is the prony brake (from the French inventor DeProny).  Just like a set of brake shoes in the drum of a car’s wheel, shoes drag against a rotating shaft or drum and force is applied until the engine’s rpm is held constant. The brakes attempt to twist about the shaft as it rotates and that twisting force, or toque is measured.  The horsepower can then be calculated (Torque x RPM / 5252).

History – Old Dynos

Old dynos actually used wooden brake shoes.  They got hot and could catch fire so it was common to cool them by pouring water on them.  Today much more sophisticated brake systems are used.  There are water brakes, which are basically a very inefficient water pumps requiring hundreds of HP to pump relatively low volumes of water.  Like the prony brake, the outside hub is free to rotate and only held in place by a strain gauge that measures the force applied at a given rpm.  Water is fed into the brake and it loads the engine.  These types of brakes require a lot of support equipment such as water tanks, water pumps to circulate the water into the brake and out to the holding tank as well as a heat exchanger -since the byproduct of absorbing HP is heat.  Hot water is not the water brake’s friend.   The benefit is these units can handle a lot of power for the given size of the brake unit itself.  I once worked for a company that tested its small 7” diameter “100 hp” water brake by hooking it up to a 350 Chevy test mule engine and stuffing 350 hp through it.

Modern Dynos

There are a group of brakes known as eddy current brakes.  They work on the principle that a metal disk rotating through a magnetic field wants to stop rotating as the field increases.  The disk can be copper or iron and will become more difficult to rotate as current flows through the brakes coils.   These brakes are similar to the electric Telma retarders used in big trucks.  They are larger than a water brake for any given HP rating, but their beauty lies in their fast response rate.  There’s no need to wait for water volume to affect the load on the engine.   The control system processor and electronics are the only limitation in response.

Eddy current brakes rely on magnetic fields and their lines of flux and their total magnetic force measured in gauss. Heated magnets lose their power to attract things – their gauss drops as temperature rises.  Since current through a brake heats it up, the brakes ability to absorb power drops with usage and heat.  Since cooling ability affects how well the brake works in the real world eddy current absorbers are rated for power absorption capacity at a standard of 3 minutes full power.  Why?  A brake might be capable of handling 500 hp when cold, but it can only handle 60 hp when used at max power continuously.  This 3 minute full power method helps when company ‘A’ makes a brake that can hold 500hp cold and Company ‘B’ makes a brake that can hold 450hp cold.  At 3-minutes full power company ‘A’’s brake may only hold 190 hp and company ‘B’s brake can still hold a good 220 hp. 

During dyno use, in most cases the eddy current brakes will never get to a point where they reach their 3-minute full power rating.    It is entirely possible to do so, for instance if a big power engine were held for several seconds at each step in a 200 rpm increment test  from 2000 to 10,000 rpm, but that is less often the case.  For the most part the air cooled eddy brake is used on and off and its periods of zero electric current while still spinning allows plenty of cooling time to keep the brake capable of handling near peak capacity.

There is another type of electric brake and that is the AC or DC motoring dyno.  Like the eddy brake they apply a load through electric means.  In this case the resistance of a motor.  The extra benefit is that they can spin an engine and/or drive line over and determine drag and inertia in the drive train.  The trade off is the huge expense and the massive size of the motors themselves.

In the motorcycle world, the inertia dyno has brought a hp capacity to size ratio that has been unheard of until recently.  Remember that the author is old, so any dyno that came on the scene between 1985 and 1995 is still new.  Back in 1989-1990 when the Dynojet Model 100 dyno rated for 750 or 800hp (only limited by traction capability) came on the scene the advertised hp capacity was absolute huge.  These inertia dynos were new and exciting. Previously the only people who had dynos were OEMs with the large GE, Horiba and Schenk dynos and the hot rodders had companies like Suska offering manually operated water brakes and Superflow offering electronically controlled water brakes. Motorcyclists had limited options.  Back in the 70’s and 80’s there was the hydraulic Serv-Equip dyno good for about 100 hp (which was fine because street bikes made at most 85 hp) and the eddy current Pratbaco good for a similar 100 hp.  They were difficult to operate with knobs to be turned while data was manually recorded on paper.  Therefore, the age of electronics made possible a new era, at least as far as motorcycle specific dynos were concerned. 

It is interesting to note that the blend of hybrid dynos that are a combination of inertia and eddy current brake have allowed for such wide range of power and versatility that one eddy current dyno manufacturer has found that their little brake can no longer be used to sell their dyno.  They used to offer the advantage of low inertia by using a light weight drum with small radius.  The small radius spun the drum at high speed compared to the 18 to 20 inch diameter drums on other dynos.  This meant smaller brake could be used and the high rpm ensured good cooling.  Unfortunately with no appreciable inertia, the dyno was limited to its 3-minute full power eddy current rating.  Inertia dynos can be run up against the load of the 900+ lb. drum without the need to enable the eddy brake.  Therefore  a high 750 - 800 hp rating can be claimed.  This obviously affects sales, so it was fun to observe the marketing changes over time.  Suddenly the same dyno was capable of 200hp.  This was absolutely necessary in the day of 150hp showroom stock motorcycles.  Later the dyno lost its 3-minute full power rating from the ads.  It was only advertised as 400 hp peak.  Clearly users who didn’t understand how eddy brakes are rated were walking away at expos and opting for units with higher peak ratings.

Why do Dynojets read differently?

That’s a great question.  It all goes back to 1985 and the venerable Yamaha V-Max.  Several magazines tested the Max and showed it made 119hp.  Mark Dobeck, Dynojet founder, was disappointed when his rear wheel inertia chassis dyno measured the Max at only 90 odd hp.   His dyno had to measure correctly so he made his software coder create a correction factor to make the Max read 119 (Note: Only the 1985 V-Max made 119 hp.  The 1986 V-Max had to comply with tighter 1986 EPA regulations and received a few changes to intake and exhaust to make it quieter.  Subsequently power dropped to 110 to 112 on the Dynojet.)  The problem with this approach is that Mr. Dobeck was missing a few things.  1) His dyno was an inertia dyno, so drive line inertia has an effect on power output on this type of dyno.   How?  Imagine taking your bike and bolting on a rear wheel that weighs 400lbs.  the bike doesn’t make any less hp, but it WILL accelerate slower, because a good portion of the power is now used to accelerate the heavy wheel.  This will show up on an inertia dyno as a hp loss.  It’s good that is does, because this helps us understand how much hp was used to accelerate the wheel. 

Dobeck never considered that the magazines were using water brakes driven off the output shaft of the transmission.  Steady state loading always shows higher hp because there is no appreciable flywheel effect when held at constant rpm.  The inertia of the bikes rear wheel, brake disk, driveshaft and couplings SHOULD have and DID affect the readings, but Dobeck never considered that as a fundamental fact.  He also ignored the losses due to gear interface. There is about 2% loss of available power for every gear to gear interface.  The V-Max shaft drive has to take two 90 degree turns to go from transmission output shaft to rear wheel. There are additional losses from bearing drag that increases exponentially with load.  There is also a loss due to drag in lubricants such as the hypoid gear lube in the bikes bearings and rear end. Another is the loss due to brake pad drag and tire deflection.

The V-Max never should have made 119 hp on the Dynojet dyno, but Mark had a formula created to fix a problem that didn’t exist.  We know the formula is complex as he simply couldn’t add a fixed amount, else a 2 hp minibike would make 25 hp.  He also couldn’t multiply by X-factor, else a 200 hp race bike might make 250 hp.  A faulty formula was created and now we have to endure in the motorcycle world with Dynojet hp numbers and brands of dynos that don’t read as high as Dynojets and therefore must be ‘bad’.  We also have to contend with people who think all Dynojets are bad by nature.  It depends on what you know and where you stand on the issue.  Either way, it’s now a messy world.

A question I get all the time: What’s the difference between your dyno and a Dynojet?

Ours is built from Dynojet model 100.  It is serial number 0162.  It was built very early in the life of Dynojet dynos.  After about the first  100 or so dynamometers, Dynojet started building a steel tank into the middle of the chassis to use as an oil tank for the possibility of a hydraulic dyno that never happened.  I didn’t talk about those earlier, but the one weird kind of dyno is the hydraulic one.  It pumps oil via gear motor.  If you restrict the flow, load on the engine rises and so does the pressure of the hydraulic oil.  Pressure x rpm x constant = HP.  The problem is oil temp changes viscosity and hp readings can vary based on run time.  Another messy situation if you want accurate readings.  The hydraulic pump dyno idea was scrapped – BUT – the good thing is that several dynos were built with a very strong chassis due to the integral tank.  Ours is one of them.

Our Electronics and Controls

Our software, control system and eddy current brake and associated hardware come from Dynostar.  Technical Training Equipment (T.T.E.) in The Netherlands builds test equipment for automotive OEMs including test stands, fault trigger systems, portable ABS and traction control test tracks and various other training tools.  Under the T.T.E. company is Dynostar, their engine and chassis dynamometer division which also owns Power Test dynamometers.

Upgrading a Dynojet with Dynostar controls and hardware costs about 20% more than going with the original eddy current brake upgrade from Dynojet, but we couldn’t be happier.  From technical support that leaves others making excuses, to performance of the equipment itself, it would have been a foolish decision to save a few $$ and buy inferior equipment.   The load control, RPM accuracy, self learning PIDs and industry leading ignition pick-up module are far ahead of anyone else.  The list goes on.

Our Dynostar unit now makes about a dozen or so adjustments to load (if necessary) in the time it takes a Dynojet to determine the acceleration of the drum and even begin to calculate how much load to apply. Our ignition module works happily with late model Harley Davidson Delphi Ion-Sensing ignition systems.  The ion sensing ignition in a modern H-D has the unique ability to retard timing without using an auditory knock sensor.  The system senses knock through the load on the spark plug, but that high voltage signal used to determine knock after combustion starts wreaks havoc with conventional inductive pick up rpm sensing systems.  Dynostar has a wonderful system that works so easily, if you never used anything else, you would wonder why everyone else has such problems with their systems.

Our Air Fuel monitors are not a dynamometer manufactuer profit based add-on option, but rather dual ECM Co. AFR Modules.  ECM is the original manufacturer of the first wideband oxygen sensor controller initially developed for NTK and Horiba and supplier of OEM engine controls and monitoring equipment to all the major automotive manufactures.

We can set the system to start at any rpm point we choose by using the eddy brake to hold that rpm indefinitely.  This allows us to take a moment set the motorcycles throttle position precisely where we want it.  Then we trigger the start of the test at the specific throttle position we want to view.  We can control the ramp rate by using the mass of the drum with any amount of addition brake percentage applied via the eddy current brake.  We can perform tests that hold the engine still at various rpm steps for a given amount of time and declare rpm stability window.   Additionally we can hold any rpm on the fly with the hand held remote.  That allows us to check and tune any rpm point and observe the torque, horsepower and exhaust gas oxygen content at all throttle positions for that rpm.

Are Dynos the Best Answer?

A dyno is not the racetrack or the real world, but there’s nothing else that is going to give you the data collection that a dyno allows.  I’ve heard many racers say things like, “Well a dyno will get you close.  You have to tune at the track”.  Usually that is said by someone who doesn’t have access to a dyno.  The way I see it, I sometimes feel like asking the naysayers, “How many times have you put Vance and Hines on the trailer headed home?”  Yes, that’s right.  You haven’t.  Every one of their race engines is run and tuned on the dyno.  They actually go on the engine dyno and not the chassis dyno.  They have that engine dialed in, long before it reaches the track.  They may do some light fuel adjustment, but the rest is chassis and clutch.  You may say, you haven’t beaten them, but George Bryce / Star Racing has.  Yeah, they throw every engine on the dyno too.  Who else?  Bob Carpenter, Ward?  The top men don’t show up at the track and guess at fuel and spark curves looking to see what gave them the best pass.  The manufacturer of your motorcycle didn’t guess at carb jetting and EFI maps.  The company who made your car ran all their development engines on the dyno to develop the fuel and spark curves.  Yes, they production cars and bikes are then road tested and further adjustments are made, but if you think guessing at fueling will get you where you want to be, go ahead and enjoy the fun of fuel adjustments daily.  Us, we’d prefer to have a well sorted fuel map before we roll out of the garage.  Our dyno gets us there.  We once did the jet swapping thing without any way to tell what was better or worse other than seat of the pants.  Right now, I’d take the worst dyno over no dyno any day.

We accept Visa, Master Card, American Express and Discover through Square.  Of course we still gladly accept cash payment too!

Send mail to elizabeth@viciouscycletuning.com with questions or comments about this web site.
Last modified: 01/31/16