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Forward flow – myths and reality

Regarding the benefits of forward flow, two questions open a heated, fiery controversy:

  • Does forward flow increase engine power?
  • Does forward flow make the rider more visible?

The increase in horsepower is what many motorcycle owners are fighting for. Of course, someone just needs a pleasant sound, but they don’t care about filly at all, but oh, these endless conversations: I’ll put forward flow, let everyone see and fly like a Boeing … with the same whistle.

The essence of direct flow is that the engine is quickly freed from exhaust gases. Yes, even faster than you expect to break from the traffic lights! The absence of obstacles inside the exhaust system, flutes and killer decibels provides an easy exit for exhaust gases.

Naturally, in this case, environmental friendliness suffers. Since nothing slows down the exhaust gases, then they are cleaned less, as well as cooled, by the way too.

– Does this mean that the engine power is increasing?

I spoke with an interesting exhaust system engineer who explained on the fingers the true purpose of the exhaust system. Look, when the engine is running, energy is transferred to the wheel, which causes the motorcycle to move. When the cylinder is emptied, the exhaust gas essentially simply leaves the cylinder. At this moment, a certain amount of energy is spent, it turns out that the exhaust system absorbs power, and does not give it an increase in the literal sense. She is her consumer. As parts of an electrician that do not generate anything themselves, but are powered by a generator. This means that it is possible to influence the increase in power due to the bandwidth. In other words – reduce energy consumption when exhausting gases… When the release is difficult, it is more difficult for the engine to function properly, because it needs to be emptied and saturated in a cyclical and timely manner.

And since the exhaust system can only absorb power, the task of the engineers is to ensure that it does not consume too much, but allows it to pass through enough to saturate the cylinder until the next cycle, efficiently remove gases and … extinguish the sound!

The increase in performance with a good exhaust system is made up of a balance between the optimal loss of power when evacuating gases, the level of sound volume and environmental friendliness.

You see, yes, that ideal forward flow is a game of balance, where there is “volume” on one bowl and “loss of power” on the other. The louder the exhaust, the greater the percentage of power loss. This is the reasoning of engineers. Although I do not argue that due to the shape of the “can” and its material, you can get different ranges of sound.

Does the forward flow make the rider noticeable?

Definitely – yes! No matter how much the public is indignant at the early trills of high-speed engines, instead of birds singing, the forward flow makes it necessary to look for a motorcyclist and wait for his appearance. It’s like an airplane that you can’t see in the clouds, but every now and then you squint into the sky at the sound.

I hear a ringing – I don’t know where he is. Often motorists and pedestrians do not notice a motorcycle simply because of its size. Because of optical illusions, because human attention is selective and we also discussed this (“Feeling of speed while riding a motorcycle”). Pedestrians look at the cars, but do not notice the fast flying point of the sportbike. But go don’t hear the bellowing chopper! Likewise with motorists. Let him not see you, but hears. This means that it is mentally preparing that you will emerge from the blind zone, like the devil from a snuffbox. The very first thing I did was to change the stock exhaust to forward flow, so that the ground behind the motorcycle would squat three meters. And in another way (I spread my hands).

Case of life. A motorcyclist friend of mine fought very hard for visibility in the traffic of Moscow. He bought bright outfit, opted for a red “gouge out” motorcycle, swapped out Ducati’s own beautiful supersport exhaust for a self-made stainless steel. The bottom line is that the sound turned out to be really loud, but disgustingly disgusting. When he drove up to our workshop, he could be heard about five minutes before arrival, even at the junction at the beginning of the avenue. Such an amazing screeching with a hoarseness and gurgling like the screams of the wounded Godzilla, screaming through the siphon of a rusty sink, could not be interrupted even by the one-liter compressors that always worked at our station.

Therefore, yes, forward flow is definitely +10 to visibility in the city. The question is, what kind of forward flow do you have, is its sound pleasant or makes everyone around you frown?

Explosive Mike also expressed his opinion regarding forward flow.

Bottom line: the best forward flow can be considered the one in which the resistance to the flow of exhaust gases is such that power is not consumed in large quantities during exhaust, the evacuation of gases is efficient, and the sound at the moment of resistance and reflection does not interrupt the eardrums of pedestrians and inspires the pilot himself. In this case, you will be satisfied with the engine performance, you will be happy to drive yourself with such a sound that does not irritate you or those around you.

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