motoTrooper
XS400 Addict
Hey y'all gather 'round while I tell thee a tale of broken eardrums and pissed of peoples...
So I'm finishing up my build:
http://www.xs400.com/threads/riven-motors-cafe-build.13403/
Riding around and addressing all the small issues that only show themselves while testing the bike on the road. Now while I like a snap/crackle/growl, and boom to the exhaust, there can be too much of a good thing. In keeping with the budget aspect of the build, I bought some EMGO reverse cone megaphone mufflers.
Love the look of them and I tried to pre-mitigate the noise and reduced back pressure by welding on the smaller outlet plates from the original mufflers to the perf core outlet plates. Riding around they were too loud. So I repacked the cores (which had a laughable amount of fiberglass) with some quality FMF mat.
Still too loud. So I bought some db killers. I sized the perf core inlet at 48mm and got those in the longest length they had. (By now the FMF mat had settled and I was able to slip the cores out without disturbing the mat.)
I wanted to use as much length of the killer as possible butting it inside the tip against the perf core.
So I removed a 1/2" of the base to slide it in further.
in place
I drilled three evenly spaced holes around the tip, plug welded the killer in place, and flap wheeled the welds flush.
I then slipped the cores back into the muffler bodies and installed the cone ends.
Now I was able to measure how much killer length I had to remove to fit into the header pipes before hitting the walls where they curve up. So took about an inch off and installed the screw-in plug bit orienting it so the bolt is on top to help prevent it from backing out during vibration.
So measured empirical results: using a Realistic Sound Meter from 4 feet behind the bike, I measured 95db at 1500 rpm before the killers. With the killers in place I measured 92db at 1500 rpm. Doesn't sound like much? Well the db scale is logarithmic so for every 10 db in scale the sound is twice as loud. So I'm guessing I reduced the noise by 30% from twice as loud? I don't know nor do I care. It's loud still but not embarrassingly so. So success!
So I'm finishing up my build:
http://www.xs400.com/threads/riven-motors-cafe-build.13403/
Riding around and addressing all the small issues that only show themselves while testing the bike on the road. Now while I like a snap/crackle/growl, and boom to the exhaust, there can be too much of a good thing. In keeping with the budget aspect of the build, I bought some EMGO reverse cone megaphone mufflers.
Love the look of them and I tried to pre-mitigate the noise and reduced back pressure by welding on the smaller outlet plates from the original mufflers to the perf core outlet plates. Riding around they were too loud. So I repacked the cores (which had a laughable amount of fiberglass) with some quality FMF mat.
Still too loud. So I bought some db killers. I sized the perf core inlet at 48mm and got those in the longest length they had. (By now the FMF mat had settled and I was able to slip the cores out without disturbing the mat.)
I wanted to use as much length of the killer as possible butting it inside the tip against the perf core.
So I removed a 1/2" of the base to slide it in further.
in place
I drilled three evenly spaced holes around the tip, plug welded the killer in place, and flap wheeled the welds flush.
I then slipped the cores back into the muffler bodies and installed the cone ends.
Now I was able to measure how much killer length I had to remove to fit into the header pipes before hitting the walls where they curve up. So took about an inch off and installed the screw-in plug bit orienting it so the bolt is on top to help prevent it from backing out during vibration.
So measured empirical results: using a Realistic Sound Meter from 4 feet behind the bike, I measured 95db at 1500 rpm before the killers. With the killers in place I measured 92db at 1500 rpm. Doesn't sound like much? Well the db scale is logarithmic so for every 10 db in scale the sound is twice as loud. So I'm guessing I reduced the noise by 30% from twice as loud? I don't know nor do I care. It's loud still but not embarrassingly so. So success!
