'Loud pipes save lives' is a wonderful culprit for making brave noise. But from very early times people thought that less sound at maximum power would be nice. And so they hit the muffler, the muffler.
That idea was described in the Motor-Rijwiel and its treatment (Third edition, 1920, price ƒ 1,50)
“The construction is very simple. The gases that come out of the cylinder are very hot and still have a relatively high pressure. To cool them and reduce their tension, they are fed to the muffler. It consists of various divisions, which are connected by fine holes. In this way the gases reach the outside air more or less gradually.
Since the gases in the muffler usually follow a very cumbersome road, on which they also experience a lot of resistance, they will have a more or less braking effect on the engine and will withdraw part of its power. With a well-constructed silencer, that power loss is also small.
However, the motorcyclist has free country roads, where a loud roar does not disturb him and he likes to go up power wants to drive at the highest possible speed, another means to allow the exhaust gas flow to pass unhindered. A valve or valve is often installed in the pipeline for the silencer. If this is opened, the exhaust gases can enter the outside air without hindrance and without having to flow through the muffler. This valve is operated from the steering wheel or by means of a pedal. However, they may only be opened if no one is disturbed by the loud roar, or causes trouble, because horses become shy, etc.
Nowadays we have exhaust systems that work the same, now electronically
Don't just think of (expensive) aftermarket exhaust systems for Harley's. At BMW they also use the system. The idea is a better sound while retaining power. But the whole muffler business only became serious when people once started doing some calculations on gas flow dynamics, pulses and waves. Before that, the open megaphone exhausts were screwed under competition two-strokes. And that was not about anything at all, except for the idea that the residual gases had to leave the building as quickly as possible.
A few Dutch people played a pioneering role in that development process of the exhaust systems
Op alfaIn the correct order they were Ab van Ginhoven, Paul Klaver, Jan Thiel and Frits Overmars. Those men started calculating things (with the slide rule and a pile of paper) and soon embraced the blessings of the computers.
And only then did it become clear to what extent exhaust systems are important for the performance of an engine
In fact, with a four-stroke, “the faster the exhaust gases are gone, the better”. Those were the heyday of the (open) megaphone silencers that were enthusiastically supplied in mildly civilized form by many English and Italian producers.
For the more genetically civilized BMW riders, Hoske made exhaust mufflers that the boxertwins sport lungs should give. But the realization that the pressure waves pulsing in the exhaust system could also have a controlling effect on the cylinder filling became increasingly clear. There are now beautiful and good replicas of those dampers for sale. But the bulk of the offer consists of cheap, costly Chinese misfires.
A Yamaha XS2 with such dampers received a spontaneous heat collapse because the dampers did not have sufficient flow. And with Chinese replica Dunstall Decibel Silencers, the 'bundles' of end pipes in the tail of the damper were mounted on a blind plate. They cost little money, but they do have capital.
We already mentioned Frits Overmars. Frits was and is a top engineer. They thought so at Aprilia. He was also good at communicating, and they greatly benefited from Aprilia.
His talent for making technically complicated things understandable is phenomenal. I spoke to him a while ago and he sent me a few columns that he made a long time ago. This shows knowledge, the eye of a detective and a refreshing sense of humor.
Power and rail pipes: Part of a column
“… The tail pipe diameter as we have just calculated also applies to four-strokes as the minimum diameter. Larger is allowed with a four-stroke, smaller is not allowed. Just look at the two 'chimneys' of a Formula One car. They have a diameter of about 60 mm at their narrowest point. The power that can pass through that is (60 / 3,06) ², or 384 horsepower per pipe; a total of 768 hp. They are currently not quite achieving that, but with over 720 hp they are still close by. ”
“While we are doing the calculations, I occasionally see a pimped black Honda CRX coupé in my neighborhood, where the exhaust ends in two impressive tailpipes, each ten centimeters in diameter, which together produce 2136 hp. The CRX is also known for its acceleration: from zero to recovery in eight seconds. ”
Was signed: Frits Overmars
Hi Rjab
What you say is correct. If one talks about the 'back pressure' that an outlet must generate, then that is the 'little clock' story of knowing that an outlet does something, but cannot explain the how and why. In terms of resonance technology, the exhaust must be tailored to the entire range of stroke volume, stroke / bore ratio, valve dimensions, steering times, inlet dimensions, ignition curve and the entire rimbim. A good outlet then indeed works like a turbo and, precisely dimensioned, ensures that fresh mixture quantities that flow into the inlet at the joint opening of the inlet and outlet are pushed back into the cylinder by a reflected pressure wave. The actual filling volume of the cylinder is often noticeably larger than the cylinder capacity. For more information, read the book:
"Wege zum Hochleistungs Viertaktmotor" by Ludwig von Apfelbeck.
With two-stroke engines, the effect of the exhaust is even greater. The holy grail of performance….
Interesting article. Totally irrelevant, but in what way is the enumeration of the names of those four Dutchmen in alfabeta order? If you write them in Greek maybe 😉 ?
Exhausts must be very precisely tailored to the entire configuration. Mixture supply, cam sticks, combustion chamber shapes, stroke / bore ratio, valve diameters, lift rates, channel shapes and diameters, etc.
For example, BMW has already screwed out exhausts among the older boxers that did a terrible job. Fitting open pipes worked like cattle thieves. The horses disappeared from the stable.
You could improve something. Depending on the entire setting.
By blue, the mutated R45 to R65,…. but just a little different… .the balance pipes in front and behind the engine block were replaced by expansion dampers. That yielded a good 6hp.
This while in many epics about the tuning of 'die Gummikuh' it was mainly advised to stay away from the exhaust with your tuner ficks. Admittedly. The dampers are still the original. The best there is…. And the great thing is that the increase in power was accompanied by an even quieter exhaust note. The change with compensating expansion damper does require The special preparation of those things and correct dimensioning. The effect is delightful.
) exhaust works as a kind of pressure wave turbo but also considerably improves efficiency. A while ago I understood that especially with 2-stroke the (expansion)