Header length theory question


2 replies to this topic
  • skillet

Posted September 16, 2006 - 06:54 AM

#1

Building a custom street bike with an NX/XR650 motor and Hawk frame. I'm looking at exhaust design. I understand the reasoning behind equal length headers in a multi cylinder engine and the results of longer vs. shorter length. I'm trying to get my head around the effects of unequal length headers coming off of the same cylinder with 2 exhaust valves and ports, like the XR's. If one was half the length of the other and they went to a collector, it seems like the exhaust pulses could be spaced such that an additional scavenging effect would take place. But it can't be that easy...

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  • XR650L_Dave

Posted September 18, 2006 - 08:05 AM

#2

Building a custom street bike with an NX/XR650 motor and Hawk frame. I'm looking at exhaust design. I understand the reasoning behind equal length headers in a multi cylinder engine and the results of longer vs. shorter length. I'm trying to get my head around the effects of unequal length headers coming off of the same cylinder with 2 exhaust valves and ports, like the XR's. If one was half the length of the other and they went to a collector, it seems like the exhaust pulses could be spaced such that an additional scavenging effect would take place. But it can't be that easy...


I don't think you can do much useful by varying the lengths of the headers from the same cylinder. I don't recall ever seeing any authoritative work in the area either, though.

I know the XR650L has different length tubes, and always wondered why, then realized its so the front wheel doesn't hit the tube when the suspension is compressed.

Dave

  • skillet

Posted September 18, 2006 - 06:12 PM

#3

Dave - thanks for the response. I agree, there probably isn't musch to gain here. I just figure that as long as I have to fabricate, why not look at possibilities? I've looked at the HRC header plans for road racing this engine and they use equal length headers entering a collector that then increases the diameter of the pipe to the "muffler." I remeber having this conversation a few years back with an Indy Car owner over way too many drinks... :thumbsup:





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