Although both bikes saw paltry...
Although both bikes saw paltry increases on the dyno without mufflers, the utter shit racket emitting from the pipes was the equivalent to stamping the word "idiot" on your helmet.
Hit the local hangout and you'll see all sorts of mods-some good and some bad. Such is the case with exhaust systems in particular. In recent years we've noticed an interesting trend-removing the stock muffler and riding with open pipe(s). A quick poll of several muffler-missing riders netted us replies like: "I felt an increase in power without the pipes and it didn't cost a penny," and: "It helped up top for sure!"
Whether you've never heard of this fad or your bike is currently lacking its mufflers, we decided to hit the dyno and see if this raucously loud mod is worth anything in the way of power.
But before spinning the drum we surveyed the many bikes on the market and found two trends. Bikes like our 2011 Yamaha R1 represent straight pipes with a catalytic converter when the cans are removed, while the Kawasaki Ninja 1000 still has a breadbox pre-muffler when the cans are jettisoned. Both bikes were used to represent a wider range of models.
On The Drum
The Ninja was first on the dyno and in stock form it quietly belted out 120 HP and 72 LB-FT with a relatively rich air/fuel ratio (AFR). With the slip-ons removed the Kawi belched free with a total of 121.7 HP and 73.1 LB-FT for gains of 1.7 HP and 1.1 LB-FT and the AFR was still safe in the low 12s.
As for sound decibel readings, since the ambient level of the dyno is so loud that it skews the dB readings, we measured the open examples in +/- dBs in relation to stock. In this instance the open breadbox muffler increased the dBs by 15 and the sound quality was atrocious. The resonance was so intense that onlookers winced in confusion.
The R1 concluded our acoustic test with several clean pulls to the limiter. When the dust settled the stock mufflered R1 belted out 148.7 HP and 73.1 LB-FT with an overly rich AFR in the high 11s. With the mufflers removed and nothing but some straight pipes and a cat, the R1 cackled out 150.3 HP and 73.1 LB-FT for a gain of 2.6 HP. The AFR leaned out roughly half a point to the low 12s.
In regards to sound, the R1 quickly exploded into an unbearably loud wail just a few thousand RPM past idle. On the dB scale the straight-piped R1 pegged our meter with readings of over 25 dBs louder than stock. Trust us, it was too loud for human consumption, while the Kawi sounded as bad as a rotten fish stick smells.
Removing the mufflers on both bikes was worth a few ponies on the dyno, but at what cost? Both bikes were so loud that a jaunt down the street had pedestrians staring in disbelief and mothers covering their childrens' ears. Both bikes were simply too loud for the street, track-anywhere. While you could duplicate these procedures for a meager gain in power, a nice aftermarket pipe looks and sounds tons better and will offer much better power gains. By removing your muffler you'll risk tickets whenever your bike is running, destroy your ears, piss off your neighbors (and riding buddies) and add another dark smudge to the biker stigma. Buy a proper aftermarket pipe if you're looking for real power and good sound.
MYTH: CONFIRMED. PLAUSIBLE. BUSTED