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A Dynamometer is essential to realizing

the full potential of today's fuel-injected

and carburated motorcycles from stock

to modified. This is the only tool that can

accurately calibrate fuel and ignition maps

or diagnose run/drivability issues in a

controlled environment. We have technicians

that are trained to tune Powervision,

PowerCommander, Thundermax, TTS,

Direct link,  Race Tuner, and a host of

others  (DC CYCLE & RACING is a certified

Dynojet tuning center) and have experience

with all H-D  tuning devices.

Equipped with Real-time Torque

module/meter, real-time O2 and Eddy

current load control, our Dynamometer is a state-of-the-art, computer-controlled, Dynojet 250I bike and trike Dyno. By simulating the best "seat-of-the-pants" road testing right in the shop, many drivability/run problems can be diagnosed in a fraction of the time.


Understanding fuel and ignition requirements

The simplest way to look at the internal combustion engine and understand what is done to increase performance is to see it as an air pump. The more air it is capable of pumping at any given time, the more power it will make (expressed as Volumetric Efficiency or VE). To get the most energy out of that air, it relies on accurate metering of fuel to that air (expressed as stoichiometric, an AFR of 14.7:1 is the theoretical ratio that results in the greatest release of available energy in gasoline). Real world inefficiencies result in an air/fuel ratio (AFR) of 12.8:1 to 13.3:1, for best power and 14.5:1, for best mileage. Keeping the AFR around 13.8 under load, get the best of both worlds.

The VE, AFR and tuning requirements constantly vary as determined by the mechanical and dynamic properties of the motor. The main mechanical parts are typically engine size (volume), compression ratio/cylinder pressure (static, corrected and dynamic), cam timing/lift, port/valve flow capacity (cfm, including the induction system), exhaust and NOS/super/turbo charging. The exhaust system is the largest, single, variable influence on how the motor processes air, the shape of the VE graph and tuning requirements. The dynamic parts are typically RPM, throttle position and load (including wind, tire pressure, terrain, gearing and luggage).

Ignition requirements are dictated by engine design properties such as exhaust (how much heat is retained), cam profiles, piston/combustion chamber shape, piston/head clearance (quench/squish), cylinder pressures, rpm limits, fuel quality and intended use.

On carburated motorcycles to adjust air/fuel ratios. We use various performance parts and kits. To install we remove the carburetors to gain access to and replace pilot jets, main jets, emulsion tubes, needles and make float height adjustments as required.

This procedure can require removing and replacing the carburetors many times until the correct ratios are accomplished. A dyno tune is the most efficient and accurate method.

Fuel Injected Motorcycles have throttle bodies and fuel injectors driven by the ECU (engine control unit) and its programming or calibration. Input from a variety of sensors allows more accurate control as engine demands change and offsets to account for environment changes.

Dyno room




Power in mechanical terms, is the ability to accomplish a specified amount of work in a given amount of time. By definition, one horsepower is equal to applying 550 pound force through a distance of one foot in one second. In everyday terms, it would take one HP to raise a 550 pound weight up one foot in one second. So, to measure horsepower, we need to know force (in pounds) and velocity (in feet per second).

Dyno Jet’s inertia dynamometer measures power just in this way. The dyno calculates velocity by measuring the time it takes to rotate the heavy steel drum one turn. The dyno measures forces at the surface of the drum by indirectly measuring the drum’s acceleration. Acceleration is simply the difference in velocity at the surface of the drum from one revolution to the next. The force applied to the drum is calculated from acceleration using Newton’s 2nd Law of, F= MA, (F)orce equals (M)ass times (A)cceleration.

Power is coupled to the drum by friction developed between the driving tire of the vehicle and the knurled steel surface on the drum of the dynamometer.




When an object rotates around a point, the object’s speed of rotation depends on both an applied force and the moment arm. The moment arm is the distance from the point of rotation to where the force is being applied. Torque is the product of the force and the moment arm. For example, think about trying to spin a drum by wrapping a rope around the drum and then pulling on the rope. If the rope is wrapped around a drum of one foot radius and pulled with 550 pounds of force, the resulting torque is 550 pounds.

The torque on the dyno’s drum can be calculated by multiplying the force applied by the drum’s radius. However, engine torque is not equal to the dyno’s drum torque because the gearing through the drive train changes the moment arm. The change in the moment arm is proportional to the ratio of engine speed to drum speed. Therefore, tachometer readings are necessary to calculate and display engine torque.




The calculation of horsepower, or the accuracy of a Dynojet dynamometer, is not dependent on the location or conditions during the measurement. The performance of the internal combustion engine however, is sensitive to atmospheric conditions, especially air density and air temperature. To compare power measurements taken at different times or places, it is necessary to compensate for differing atmospheric conditions.

Correction factors are used to compensate for differing operating conditions while measuring engine horsepower. The typical correction factor is calculated based on the absolute barometric pressure, air temperature and the water content of the air used by combustion by the engine under test. The correction factor attempts to predict the engine horsepower if the engine were tested at sea level under standard pressure and temperature conditions.

Absolute barometric pressure is a measure of how hard the air molecules are being pushed closer to one another. The unit of measurement is typically inches of mercury (inches Hg). The more pressure, the more molecules there are in a liter of air and the more air the engine “gobbles up” during the intake stroke. Absolute barometric pressure is equal to relative barometric pressure only at sea level. Relative barometric pressure is reported at airports and by weather barometers. A good approximation for converting relative barometric pressure to absolute pressure is:


AbaHg = RelHg – (Elev/1000)


AbsHg is Absolute barometric pressure

RelHg is Relative barometirc pressure

Elev is test location elevation in feet above sea level.


Humidity is the percentage of a volume of air that is occupied by water vapor. Water vapor displaces oxygen and reduces the amount of combustion air ingested during the intake stroke. Air temperature is the temperature of the air entering the intake system of the engine under test. In some cases this is ambient air temperature, but in other cases the intake air is significantly heated by the engine and is different than ambient air. Heat tends to spread air molecules apart. So as temperature increases, there are less molecules in a liter of air and less air is swallowed during the intake stroke.

Dynojet’s WinPEP 8 software uses the SAE’s latest correction formula (June 1990). This formula assumes a mechanical efficiency of 85% and is much more accurate than earlier formulas at extreme conditions. The most common correction factors are sae,din,eec,jis or std. DC CYCLE & RACING uses SAE correction factor!             (On average, sheets that are printed in STD correction factor will be inflated 3-7 HP  Keep this in mind when trying to compare Dyno sheets). 


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