Quote:
Originally Posted by RoughSilver92
Harvey, I'm not understanding the benefit of having the 3 pipes run into the expansion chamber without the use of a collector. And please don't get me wrong, I'm not questioning your knowledge. In fact I'm certain that you know more about the voodoo of engine tuning than I do, that's why I ask. But from what I have read from David Vizard, power is made in the collector. He even says that equal length primaries are not as important as a correctly tuned collector. Is the difference in the type of engine? Vizard generally writes about old V8's. As you explained in your camshaft thread, there are differences in what our engines like and what those like. Is this another one of those instances?
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That’s ok mate, I know that it runs across the accepted theory, but as you say, it is another one of those instances.
The older ‘low engine speed’ theory, is based on the inertia of the exhaust gas flowing down a pipe, to create a low pressure behind it. They used this pressure to start the flow of inlet gas into the cylinder, during the over lap period. There is the theory that the flow would suck the exhaust gas out of the next cylinder. That worked up to a engine speed that was low enough, and the overlap was long enough to do it, but as this gas flow only travels at about 300 ft/sec, it was too slow for engines that had to develop there torque at 6/7000 rpm. The main function that a V8 header has is that, when the long overlap is used, there is a huge amount of interference between cylinders, some only 90* apart, so the header branching had to be very long to prevent it.
To the present, the exhaust that we have is the modern high-speed type; it does not rely on the inertia and overlap to induct the inlet air. It uses the sound wave pressure that is developed in the engine pipes, from the exhaust valve down to the third cat. This wave travels at 1700 ft/sec, fast enough for the highest engine speeds. This is the difference that changes the way we design headers, because, they have different functions to do.
We have three cylinders (the other side will be the same) they exhaust 240* apart, there is no chance that one cylinder will push exhaust gas into another cylinder, so the branching is kept as short as possibly. The three cylinders then use the exhaust pipe, from the exhaust valve to the 3rd cat, as its own tuned length resonate system, returning all the negative pressure back to the cylinder that needs it, to induct its air. It works the same as Toms three pipe header, but only needs one pipe, to do it.
To answer your question “, I'm not understanding the benefit of having the 3 pipes run into the expansion chamber without the use of a collector”.
The three pipes have to serve the three cylinders, the same as the STD single pipe does. It’s the end of the pipe that makes it or breaks it. Each pipe has to enter the chamber separately to return its energy back to its cylinder, when the three pipes join into a ‘collector’ pipe, the wave will divide into three, sending one third of its pressure up the other two pipes. The original one third enters the expansion chamber to return a weaker negative wave back to the end of the three pipes, divide into three again. Leaving precious little to work the cylinder that started it.
The exhaust gas inertia and the sonic wave can’t be treated the same. Exhaust gas has mass, hence inertia. It can flow gas pressure past another pipe and draw a low pressure in it. The sonic wave will divide send the same pressure up both pipes.
That is why we keep the branching short and the whole header system as compact as possible to preserve the pressure returned to the cylinder.
Does this answer your next question?
Harvey.