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Everything Dirt Bike
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<blockquote data-quote="snowflake" data-source="post: 60288" data-attributes="member: 152"><p>FMF, the creator of the "Power Bomb" stated a much different purpose for that design some time ago. Four stroke headers can be tuned using pipe length and diameter to sync with the pressure waves produced by the exhaust in such a way as to cause a wave of negative pressure to arrive at the exhaust <a href="http://www.thumpertalk.com/forum/archive/index.php/t-938306.html#" target="_blank"><span style="font-family: 'verdana'"><span style="font-family: 'verdana'">valve</span></span></a> as it closes, thus aiding both the extraction of the last bit of exhaust and the induction of the incoming fuel/air charge. This works, but like any harmonic event, it is most effective within a fairly restricted range of engine speed.</p><p> </p><p>FMF claims that the PB (which is not a simple expansion chamber, but a perforated section of pipe with a chamber around it) acts on the pressure waves within the pipe in such a way as to make the header "appear" to the engine as if it has no defined length, causing it to be less effective at peak efficiency, but more effective over a wider range of RPM. At least in the case of the PB header for an '03 YZ450, this does seem to work.</p><p>grayracer513 from tt <img src="https://www.dirtbikeaddicts.com/static/images/smilies/smile.gif" class="smilie" loading="lazy" alt=":)" title="Smile :)" data-shortname=":)" /></p><p> </p><p>although the stock wr system sucks, even with the baffle completly removed (in which case the exhaust is heavy, loud, and congestive), I saw a big improvement down low when I put my fmf full system on (powerbomb with powercore IV)</p></blockquote><p></p>
[QUOTE="snowflake, post: 60288, member: 152"] FMF, the creator of the "Power Bomb" stated a much different purpose for that design some time ago. Four stroke headers can be tuned using pipe length and diameter to sync with the pressure waves produced by the exhaust in such a way as to cause a wave of negative pressure to arrive at the exhaust [URL="http://www.thumpertalk.com/forum/archive/index.php/t-938306.html#"][FONT=verdana][FONT=verdana]valve[/FONT][/FONT][/URL] as it closes, thus aiding both the extraction of the last bit of exhaust and the induction of the incoming fuel/air charge. This works, but like any harmonic event, it is most effective within a fairly restricted range of engine speed. FMF claims that the PB (which is not a simple expansion chamber, but a perforated section of pipe with a chamber around it) acts on the pressure waves within the pipe in such a way as to make the header "appear" to the engine as if it has no defined length, causing it to be less effective at peak efficiency, but more effective over a wider range of RPM. At least in the case of the PB header for an '03 YZ450, this does seem to work. grayracer513 from tt :) although the stock wr system sucks, even with the baffle completly removed (in which case the exhaust is heavy, loud, and congestive), I saw a big improvement down low when I put my fmf full system on (powerbomb with powercore IV) [/QUOTE]
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