aus einem Dragster Magazin von 2011:
" ... Engine exhaust works on a similar principle, with mechanical pressure coming from the engine side. As the combustion process ends, the exhaust valve opens, releasing the pressure into the exhaust system.
The air moves from the high pressure chamber to the low pressure exhaust. The rate at which the exhaust gasses move is directly related to the initial pressure inside the header (and exhaust system as a whole).
This is called “blowdown” and is the difference between cylinder pressure and exhaust system pressure. Excessive blowdown pressure means less gas moving into the header on its own, requiring mechanical expulsion (pump action, i.e. piston movement). Reducing blowdown increases the rate of gas movement in the initial stage of the process.
Once past the initial blowdown expulsion, when the pressure between the combustion chamber and exhaust system have equalized, the piston takes over, providing the pump action needed to expel the rest of the exhaust and push it along its way through the exhaust until the piston reaches TDC (top dead center) and the pump action ceases.
The exhaust gasses do not stop when the pump action is finished. The inertia of the hot gasses keeps it moving through the pipe. The exhaust pulse is a not a single action, one blast and it’s over, the repeated pulsing functions like a waveform, just like sound waves. If it were blasted into open space (as in no header or manifold) it would have no positive effect on the engine.
Instead, that waveform pulses through the tubing, pushing the gasses in front of it, while pulling the gasses behind it. This creates a vacuum behind each pulse. Overlap between the intake and exhaust lobes of the camshaft means that as the intake valve is opening, the exhaust valve is still open, allowing that newly-created exhaust vacuum to draw fresh air and fuel into the combustion chamber, beyond what is possible through normal atmospheric pressure in the top side of the engine. This process, called scavenging, is one of the biggest benefits of headers over manifolds.
The basic principles of exhaust flow are fairly simple; getting the maximum exhaust from point A to point B is where things get interesting. There are many factors at work in the scavenging and blowdown process. Primary tube length and diameter are the main components in the fight for horsepower and torque. From here, we will discuss the mechanics of headers in terms of short, mid-length and long primary tubes.
“Effective header primary tube and component geometry attempts to take advantage of two distinct forces occurring inside the header to increase performance” said O’Neil, “One is the kinetic energy of the gas stream and the resultant low pressure area behind it, and the other is the considerably greater energy of sonic finite amplitude waves that originate upon the opening of the exhaust valve.”
In terms of primary length, amplitude wave tuning is limited to long tube headers. Short and mid-length headers are simply too short to take advantage of the length of the waveform. The most common use for shorty and mid-length headers are cost and clearance.
These two factors will override the desire for a long-tube header, as those two factors can be deal-breakers. If it doesn’t fit, it doesn’t fit. That doesn’t mean they are useless. Shorty headers are designed to be as effective as possible in terms of getting the flow moving by removing restrictions ..."
Ich finde, daß es hier sehr schön erklärt wird.
Wir reden also über ZWEI Wellentypen!
Wer sich ernsthaft mit dem Thema im Detail auseinandersetzt, wird irgendwann feststellen, daß für den normalen Kack-SR-Motor im Serientrimm 30mm Krümmerinnendurchmesser mehr als genug sind. Und extrem getunt (600+ ccm und 45+ PS) reichen amS auch 35mm.
Die Tröte hintendran ist weitestgehend nur für`s Auge (und Ohr) und hat wenig positiven Effekt auf die Performance hinsichtlich des Füllungsgrades und damit der Drehmomentkurve. Es sei denn, sie stellt geometrisch eine Verlängerung des Krümmers dar.
Gruß, Theo
![:]](https://www.sr500.de/images/smilies/pleased.gif "Freude"){kind=small}
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