2017 Kawasaki Z125 Pro Yoshimura RS-2 Exhaust Install and Dyno Test Video

Watch as we slap Yosh’s RS-2 exhaust on a Z125 and then flog it on the dyno.

If you've watched this walkaround video of the Kawasaki Z125 Pro, you know that the Z sounds like a sewing machine. It's so quiet! And while we like the look of the under-engine exhaust, there's surely room for improvement. Lucky for us (and all the actual Z125 Pro owners out there) Yoshimura recently released its RS-2 Mini exhaust system for the 2017 Kawasaki Z125 Pro (click here to see our First Ride review).

First up, some background. The Yoshimura RS-2 Mini is mandrel-bent from brushed stainless-steel tubing and has a carbon-fiber-clad muffler. It's a beautifully crafted piece and sells for $499. For that stack of cash Yoshimura says your Z will lose 3 pounds and get a 5 percent boost in peak horsepower. Well we've got tools, a scale, and a dyno, so we decided to bolt the thing up and see what it's like.

The installation was pretty easy and took all of 30 minutes. The hardest part was mounting the Yosh muffler bracket. It bolts to the right-side passenger footpeg assembly (instead of to the underside of the swingarm pivot as on the stock system) via two U-clamps, and getting the hardware installed takes some dexterity and patience.

On our scale the stock pipe weighed 8.4 pounds. By comparison, the Yoshimura system weighed just 5.3 pounds. That’s a 3-pound savings, just like Yosh claims. On the dyno the bike’s peak output jumped from a pavement-rippling 8.69 horsepower to 9.14. That’s an increase of 0.45 horsepower, which doesn’t sound like much, but equates to a hair over a 5 percent increase. If your 100-horsepower bike gained 5 horses with a 30-minute bolt-on (and no fueling changes), you’d be pretty stoked, right? Besides bumping peak figures, the RS-2 adds thrust across the rev range.

Kawasaki Z125 Pro dyno test
Blue is stock, red is with the RS-2 Mini installed (with no baffle). Believe it or not, some aftermarket exhausts don’t actually improve power. That’s not the case with the RS-2 Mini, which pushes the Z’s output up across the board. With the addition of a fuel controller (or ECU reflash) and some intake mods, a solid 10 horsepower isn’t far off.©Motorcyclist

Now the sound. The RS-2 is LOUD. It sounds decent at idle and partial throttle, but when you get on it (and let’s admit it, the Z is going to spend a lot of time wide open) the pipe is obnoxiously loud. Even with the included quiet tip installed, your neighbors will still hate you. I guess that’s one of the reasons this is a race-only exhaust!