Always onwards into the realm of investigation and dissection... "trust the
science"!!!!
Ever wondered what's inside a 912's factory Rotax muffler?
Today's episode of "shut that noise up" was spent looking at the back end of the
rotax; running the numbers on the factory stock 912is exhaust muffler... how
well does it actually look on paper?
Well, let's tear it apart and find out?!
Thankfully no destructive work was required; and no animals were harmed in this
episode.. these days we can simply grab a CAD model and whiz it through some
predefined plugins and see what gets spat out... personally when i first turned
the cad viewer to xray i was astounded, i said to myself "that is a joke; that
won't be doing a bloody thing... what's the replacement price on that
again?!"...
let's come back to that knee jerk assumption later...
So we ran our pre calc's, established our base frequency range for 5000rpm, and
got to work preping the model for analysis.
Several tests were run looking at low band, medium band, and wide band results;
the focus here is primarily on the low band results.
Well, the low band results showed zero attenuation of sound transmission until
320Hz with awesome attenuation capabilities of 32db at 460Hz!!! This is great!!
Only problem being 460Hz equates to 12600rpm, and 320Hz equates to 9600rpm
so my knee jerk assumption appears supported.
So the factory 912is muffler is as affective as that of a Chonda generator, i.e,
empty expansion box with pipe going in and pipe going out...
To be fair the muffler does provide affective mid range attenuation in the
frequency
range most noticeable for human hearing, which is mostly the higher frequencies
being generated by the muffler itself.
It would be great to compare a CTK muffler but i won't be cutting 181's unit
apart
any time soon to CAD it up.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510550#510550
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