What is a Dyno?
A Dyno or Dynamometer is a tool for measuring the power produced by an engine, (in our case via the rear wheel of a motorcycle). An inertia dynamometer provides a fixed inertial mass load and calculates the power required to accelerate that fixed, known mass and uses a computer to record RPM and acceleration rate to calculate torque.
The Dynojet Research Model 250i in use at Valley Motorcycles is a combination Inertia and Load Control Dynamometer that is perfect for engine break-in, durability testing and fuel injection mapping.
Reading Dyno charts
The most commonly found of all Dyno Charts show Power (HP) and Torque (ft-lb) as a function of RPM. At Dyno Bike Solutions we like to maintain our Y axes (HP & TQ) on the same scale, therefore Torque is the larger value below 5252 RPM and Horsepower is the larger value above 5252 RPM. (HP=TORQUE X RPM / 5252).
A large capacity V-Twin might not rev hard but the stump pulling torque will be noticeable below 5252 RPM. Most metrics and inline 4’s make their power above 5252 RPM so the Horsepower number is the larger of the two.
When comparing Dyno Charts always take note of the correction factor (CF) and smoothing. If these are not known the numbers can be pretty much considered as ball park.
Atmospheric Correction Factors that are used to compare an engines power output from one day or location to another. These factors can be rather confusing and even deceptive. Many would assume their engine’s horsepower as an “etched in stone” number however we also know that the engine will make very different power on different days. Excluding other factors like engine temperature and quality of fuel used, the engine output is very dependent on the amount of oxygen in the air. So the only way to compare an engine’s horsepower is to correct the output on a given day to some standard.
There are 6 Correction Factors, commonly in use when measuring the output of an internal combustion engine. At Dyno Bike we predominantly use that from the Society of Automotive Engineers (SAE) as most information found that relates to a Harley’s power output is corrected to SAE.
The smoothing factor is the amount of averaging that takes place so that any spikes are not misread as greater peak HP or TQ values. As with Correction Factors, always make sure you compare apples with apples.
On the next page the printout gained 6.11 Horsepower (7.2%) by using different correction and smoothing factors alone.
What is meant by AFR?
A typical performance tune on an injected Harley-Davidson® has a target AFR of 13.2 to 1 at high RPM or at wide open throttle. The target AFR for cruising is a little leaner at around 13.5 to 1, mainly to improve fuel consumption. Air-fuel ratio (AFR) is the mass ratio of air to fuel present during combustion. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, or “stoich”. For petroleum fuel, the stoichiometric air/fuel mixture is approximately 14.7; i.e. the mass of air is 14.7 times the mass of fuel. Lower than 14.7 to 1 is richer, greater than 14.7 to 1 is leaner. AFR is an important measure for performance tuning. (Lambda is an alternative way to represent AFR). The graph below shows how the stock tune is too lean at low RPM and too rich at high RPM.
In its simplest terms, an Electronic Fuel Injection (EFI) system is a computer controlled fuel delivery and ignition system. This electronic Engine Control Unit (ECU) reads various sensors located on the bike and makes the determination of how much fuel to allow the engine to have based on this information. The computer will open and close the injectors allowing gasoline into the engine based on the sensor inputs and the fuel map programmed into the computer. The various sensors (RPM, engine temperature, air temperature, throttle position, manifold pressure, crankshaft position etc.) provide information on operating conditions and load on the engine.
Fuel Injection Adjustment Units
The Screamin Eagle Street Performance Tuner Kit and the Power Commander are fuel injection adjustment units that influence the bike’s stock ECU (Electronic Control Unit).
The Sreamin Eagle Street Performance Kit is OE for Harley Davidson. The specialised tuning software in conjunction with the Dyno ensures a high quality permanent tune to your Harley’s ECU without any additional on board hardware remaining on the bike after the tuning process.
The Power Commander (PC) uses original equipment style connectors, so no splicing or cutting of the harness is required. Changes are made to the bikes fuel and, in some cases, ignition curves via the PC’s onboard microprocessor.
In both cases we are able to offer a large area of adjustment to the bike’s ECU accommodating any changes to the equipment of the bike and ensuring the bike is operating at maximum performance.
What is a Map?
A Fuel or Timing Map is a lookup table (similar to a spreadsheet) that the ECU uses to determine the outcome under varying conditions.
The most common Map or table that requires altering (called Tuning or Mapping) is the Fuel Map. Fuel Maps typically use Throttle Position or Manifold Absolute Pressure on the X axis and RPM on the Y axis. By adjusting the values contained in the table the fuel can be precisely altered to suit the engine being controlled.
A Fuel Map can contain over 400 different values for each cylinder, delivering far more adjustability than can be found in a carburettor. A high revving inline 4 can have as many as 800 different values; however each cylinder will be much closer to that found on a V-Twin.
A “Canned Map” or “Downloaded Map”
is a copy of a map created for a similar engine (incl. modifications) operating in a similar environment, whereas a “Custom Map” is one that has been developed for the actual motor being tuned.
The highlighted cells in this picture show fuel being added. Positive numbers ADD fuel, Negative numbers SUBTRACT fuel.
As this bike has had some radical changes the Map is altered significantly from stock.
Individual Cylinder Tune
Additional to the Canned and Custom Maps there is also the option of tuning all cylinders alike, “Basic”, or individually tuned “Advanced”.
Front and Rear cylinders on a V-Twin differ significantly. In fact any two motors, alike in every possible way, will still have variations in power and tuning requirements.
The highlighted regions of the Map below show the variation between a front and rear cylinder on the same engine.
Air Filter Comparisons
The first step in enhancing the performance of your V-Twin is to improve breathing with a free-flowing air filter.
This model K&N estimated a 12.05HP gain. At 5200RPM we measured 11.1.
Bang for your buck you won’t beat this!
Free Flowing Pipes
An aftermarket exhaust system can enhance or reduce the power output of the bike. Additional noise does not necessarily equate to additional power.
20 HP difference at the rear wheel from a 75HP Harley? A poor system can lose 10 HP whereas a good system can make 10 HP.
This is the same engine with 3 different exhausts. The best power was produced by the quietest system (which also has the best note).
Once the intake and exhaust side of things are taken care of, the limitations to the standard tune become more evident.
There are a variety of tuning devices on the market but our preference for Harley Davidson is the OEM Screamin Eagle Race Tuner. For other bike makes Power Commander. These devices allow us to connect directly to our Dyno through the relevant software so that the best results can be obtained.
This Rocker C had a Canned Map in a Power Commander that was too rich in the mid-range and too lean at the top end.
Once your bike has a Fuel Injection Adjustment Unit either Super Tuner or Power Commander onboard, almost any mods can be catered for.
Bolt-in cams are great for those that don’t want the added expense of custom engine work. The motor internals remain standard other than opening the camchest. (Naturally, upgrading the cam bearings & / or timing chain takes place at the same time).
The installation of timesaving adjustable pushrods also alleviates the need to remove the rocker boxes.