Does Harley Davidson's escape pod need a jet?

Here is one of the questions that many injection motorcycle owners are asked, and curiously, the most variety of answers generates. I am going to try to clarify the why and the coils, so you can get your own conclusions with the appropriate information.
Electronic injection or EFI has begun to be used massively in motorcycles relatively a short time, displacing the traditional carburetor. Regarding this change there are opinions of all kinds, but it is a demonstrated fact that the injection works much better, and more power, lower consumption (and lower emissions) and more softness than with the carburetor is achieved. It is as if we had the perfect carburetor, with hundreds of diffusers and circuits at the same time. Logically, provided that our injection system is well calibrated ...
But what happens when we change the escape, the air filter, the camshaft, etc. To our motorcycle?

The engine works with air!
Basically what we are doing is varying the volume of air that enters and leaves the engine. Indeed, the engine works with air, which is compressed and burned inside the combustion chamber to produce movement. At more air, more power (that is one of the reasons why air filters and escapes of greater flow) are installed, but we must not forget that the combustion of that air is carried out when mixing with gasoline. It is there when our carburetor or our EFI system come into play. They are responsible for injecting the amount of gasoline necessary for the combustion of the air that enters the engine to occur.
A carburetor performs this task by depression, if more air enters, depression varies and consequently the amount of gasoline that enters, so somehow is self-compromise (this is only true to some extent, because generally there is generally to Change the diffusers and "re-carbure" so that everything goes perfect).
In an EFI system, however, gasoline is injected under pressure directly into the admission nozzle. The moment and the amount of gasoline to inject them decides the system computer (or ECU, of Electronic Control Unit). The amount of gasoline injected will depend on the information that the system sensors provide to the ECU (RPM, opening of the accelerator, air temperature, atmospheric pressure ...) with these data and based on reference values ​​programmed in some tables ( Maps) ECU decides how much gasoline will be injected.
These scheduled tables constitute the mapping of the injection system, and basically they tell the ECU how much air is entering certain RPM and a certain opening of the accelerator, and how much gasoline it must be injected.
If we change any component that influences this air entry or exit (exhausts, filter ...) we have to communicate it to the ECU, that is, we must re-map the injection. If we do not, the ECU will work with the appropriate values ​​for our original escapes and filters, which will lead to our engine to work too “poor” of gasoline. In the image you can see how the map changes with a simple escape change.

If to an engine that to meet the emission regulations, it is already “poor” of the factory, we add this problem, we will have an engine overheating, and we remove years of life ... regarding the “poor” or “rich mixture "You just have to know that the ideal mixture for perfect combustion is 14.7 parts of air for approximately 1 gasoline. A poor mixture generates excessive heat in the engine, and a rich mixture makes us VIP clients of the gas stations ... In neither case the motorcycle will be well well, and we will not obtain the expected power and torque.

What does the escape have to do with all this ...
Most people see quite clear that if we put an air filter that lets the mixture pass the mixture, it will impoverish, since we will have more air for the same amount of gasoline.
What is not so clear is why the escape can cause the same effect. To explain this in a simple way you have to talk about waves that occur when the exhaust gases come at high speed through the tube, creating a vacuum that generates waves that circulate to the engine, contrary to the gases of Exhaust, and how correctly employed help a better fill in the cylinder in low and half rpm, where the motorcycle is most used. These pressure waves are technically known as backpressure or setback waves.

If we change the escape for another more open these waves will vary, and consequently the filling of the cylinder will increase, so it should also increase the amount of fuel so that the mixture is adequate.
The injection switchboard has no way to correct these changes automatically, not even the models with oxygen sensor or Lambda probe (Dyna from 2006 and the rest of the models as of 2007, since the correction it can make is minimal .

Therefore when we modify the escape or admission we must rewrite the air tables of the ECU (technically volumetric efficiency tables). In doing so we are informing the injection system of the real amount of air that enters and leaves the engine, and the ECU will adjust the amount of gasoline in concordance. We will have a motorcycle that will roll perfectly, without pulls, with good acceleration and without excessive “petartments” when removing gas. And, above all, our engine will roll happier and colder, something to take into account in a large -displayed air -cooled engine.

Then, how do we do it?
There are different ways of rewriting or correcting volumetric efficiency (VE) or increasing the amount of gasoline that the system must inject. There are systems that intercept and modify the signal that the ECU sends to the injectors, simply increasing the opening time of the injectors. These systems can be programmed manually by potentiometers or buttons (Cobra FI2000R, Arlen Ness Big Shot ...). An evolution of these devices are those that are programmed by software, where we can see the different tables and change the values ​​(Dynojet Power Commander III , Daytona Twin Tec Tuner II ...). Some of these devices incorporate as a novelty a function of self-learning, which means that they themselves rewrite the tables (Terry Components Terminal Velocity, Accel SLM, Power Commander V ...). Finally we have the most sophisticated models, which write directly on the tables of ECU itself and usually have self-learning and advanced functions (Dynojet Power Vision, Screamin 'Eagle Super Tuner, Thundermax, TTS MASTERTUNE, FUELPAK FP3 or FP4 .. .).

In This other article We talk about the differences between them and how to choose the right device and program it.

Conclusion:
At this point, although some of the concepts previously explained still sound a bit weird, surely you have quite clear that it is really necessary to act on the injection and re-mape system when a component is changed that modifies the amount of air that comes out or enter the engine. From a simple change of exhausts and/or air filter, to cylindrated modifications, camshaft trees, turbo or admission body, you will always have to modify the injection, or in other words, inform the ECU that has been installed New components, so that the motorcycle goes soft, does not hot, does not consume too much and accelerate as a true Milwaukee locomotive.