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Collector box function

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Athame57:
I hope this isn't a Dumbo's question  ;) but what does that collector box half way along our exhaust system do? Actually I'm asking because the web is producing different answers, also because I nearly developed a hernia today fitting a new one with downpipes.

Sesman:
Rust away.

Athame57:

--- Quote from: Sesman on March 28, 2025, 05:22:49 PM ---Rust away.

--- End quote ---
That much I've noticed, I make efforts to control it though!  ;D

K2-K6:
They are akin to musical instruments, trumpet, trombone etc, tuned to make use of pressure changes.

The "headers" entering that collector section with it's change in volume send a negative pressure wave back up the pipe it's coming from (often, possibly wrongly, referred to as "back pressure " ) that helps to scavenge the combustion chamber by that negative effect just as the exhaust valve is coming to a close. This to improve spent combustion extraction and cylinder efficiency. Also, as timing overlaps on camshaft to have both valves open at that stage, it helps to pull in the next intake volume from carburettor. 

That whole process, from the headers, is usually designed into system by altering header bore/volume/length to specifically "harmonise" at peak engine torque RPM  (is that about 8,500 on 400 ?) This to bring peak efficiency in output and so maximum effort from the combustion.

The rest of the pipe, out through silencer to end exit, effectively does the same for much lower rpm. The overall pipe length being so much longer causes that negative "signal" to take longer in getting back to combustion chamber, usually arranged by the manufacturer to harmonise with low rpm running to help with engine response through that often used range.

The whole ensemble aimed at best combustion potential enhancing "tune" through the operating range.

As extreme example in contrast, a F1 naturally aspirated engine will have extremely short, wide bore, truncated headers, very short collector/outlet etc, all focused just on absolute peak very high rpm output with no other consideration.

400 Cafe Racer:

--- Quote from: Sesman on March 28, 2025, 05:22:49 PM ---Rust away.

--- End quote ---

After starting, Don't stop the engine until the exhaust is really hot, this will help to get rid of condensation and rust formation in the collector box.  8)

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