stepped headers

[Stan]

The Smith / Morrison book, which seems quite a respectable resource, considers the stepped pipe and concludes that the best design for a high-performance 4-stroke single is a straight or tapered (diameter increasing with distance from the exhaust port, natcherly) header with a megaphone silencer. Is there anyone out there sticking stepped pipes on their singles? Not that I know of. If anything, the Formula-rules (anything goes, almost) singles roadracers seem to like the megaphone. Exhaust is just one parameter of many, and for racing-profile engine development to be successful they all have to be considered in concert. For peak volumetric efficiency, the time-pressure signature of the exhaust needs to match valve timing and the signature of the intake tract, etc. The KLR's stubby intake tract doesn't help matters if you're looking for peaky output at big single rpms, yet almost no loud pipe loving in-duh-vidual would even consider the need to look at intake length. Getting all this right is a lot of work. Lastly, the notion of turning the agrarian KLR mill into a peaky racer wannabe seems, IMHO, ill-conceived. I can't see how a narrow power band would make the KLR more enjoyable. -S bigfatgreenbike wrote:

> > >cwsdist@... wrote: > > > >>I'm looking for information on what has been done with exhaust >>systems on KLR's. Anyone with a stepped header? Any idea how much HP >>gain? I'm in the process of designing a stepped header and can with a >>local custom builder and would appreciate any feedback on what you've >>done. >> >> >> >> >The general consensus is the exhaust is not really the biggest >constriction. You will need to to a bunch of other mods to see any >significant power gain, mods to the airbox, head, carb etc. > >A stepped header has not been tried, to my knowledge, and if you get the >step in the right place it might help. > >

[bigfatgreenbike]

THESQUASHER@... wrote:

>--- In DSN_klr650@yahoogroups.com, "cwsdist" wrote: > > > >> I'm in the process of designing a stepped header and can >> > > >what is a "stepped header" ? and how does it give more power? is it >like a megaphone exhaust? > >

Google for "power bomb" header, I think FMF makes it. Works like an expansion chamber does on a two-stroke, optimizing cylinder scavenging and filling at certain RPM, depending on it's size, shape, and position. I know the theory, nothing in practice. Short of building ten different variant and dynoing them all, I have no idea where to start. -- Devon Brooklyn, NY A15-Z '01 KLR650 '81 SR500 cafe racer "The truth's not too popular these days....." Arnold Schwarzenneger, in The Running Man

[Stan]

Judging by the literature, it looks like there are two types of these: The first type seems to be an inexpensive approximation of a tapered tube header, built up from two or more pieces of tube of slightly increasing diameter. This, or the tapered tube, looks like a generally good option. Another type is made of two pieces of tube with significantly different cross-sectional area. This has been invented a long time ago for self-scavenging diesels, and is not as good. The low pressure duration for overlap is increased and works well at really low rpms (e.g. 1K rpm diesel), but at higher rpms the desired effect takes place for every other cycle only due to the way the two pipe frequencies combine. -S