SC-Project S1-GP Review: Slip-On Sportbike Muffler

From a visual standpoint, a nicer muffler, at the very minimum, is almost an obligatory addition to any new motorcycle. There are many to choose from, and the first question is whether you want a full system (that eliminates the catalyzer) or simply a replacement slip-on muffler that slips on over the existing pipework.

A full system is always much louder than stock. A slip-on can be louder, though not always. It depends on whether the catalyzer on your bike is inside the stock muffler or not. If your new slip-on eliminates the catalyzer, the exhaust note will be much louder. For example, we added the SC-Project S1 slip-on to our test Suzuki GSX-R1000R. It has the catalyzer contained within the enormous stock muffler, so the slip-on eliminated the catalyst. Man, after the switch, the exhaust was crazy loud—but it sounded fantastic.

For a significant performance increase, you’ll want to go with a full system. The S1 slip-on on the GSX-R1000R added about six horsepower to the motor’s output. While that’s not to be sneezed at, in the real world, the Gixxer is so insanely fast that it doesn’t make a very noticeable difference from the cockpit.

So do your research first and decide on which way you want to go.

The Kawasaki Z900 was launched in 2017 and quickly gathered a loyal following, and you can count me amongst those fans. It’s a relatively simple recipe for a modern machine—upright naked riding position, inline-4 screamer motor,  simple (and now-adjustable) suspension, limited electronics, and basic brakes (ABS became standard in 2020).

On the face of it, there’s nothing too special about the Z900, yet somehow Kawasaki got this one right—it’s awesome. The inline-4′  screamer’ motor quickly ramps up and revs to the moon, with a linear powerband to the rev limit.

The chassis is exemplary, with neutral, intuitive handling. The upright riding position and pleasant shoulder-width handlebars ensure a nice fast turn-in without making the bike flop into a corner. The suspension is softly sprung—perfect for the street—yet the damping is firm and quick reacting. As a result, the Z900 floats firmly across the crappy California roads with ease.

It all adds up to the Kawasaki Z900 being one of the easiest machines I’ve ever ridden fast. Although it may be a bit squishy on track (I assume), it behaves impeccably when ridden very fast on the street—just my kind of motorcycle.

Even the stock Euro-4 compliant exhaust on the Z900 is pretty good compared to some. That is to say, it isn’t heinously ugly, and it does have a pleasant and surprisingly throaty exhaust tone. However, “pretty good” just won’t quite cut it at Bike Night with your buddies, as I found. We all have standards. So yes, it had to go.

For the Z900, I had no desire to go the full-system route. Truth be told, on the track, I want my exhaust as loud as possible. However, on the street, I prefer a nice-sounding pipe that doesn’t attract too much attention from our LEO friends. On very long rides, an excessively loud exhaust can get fatiguing. I prefer something a little more restrained—not too much, but a little.

The Kawasaki Z900 has its catalyzer in a large metal box under the engine, so any slip-on would have a negligible effect on the note coming from the exhaust. It also meant that any slip-on would not have any discernable impact on the performance. No matter—that Z900 is faster than all get out anyway.

So, it all came down to looks. I like the MotoGP-style ‘shorty’ mufflers that poke out from under the bike and stay somewhat discreet. I’ve discovered that I’m also a big SC-Project fan. Their hand-crafted titanium (and carbon) pipes are nothing less than moto-porn. They’re light, they sound great, and depending on which one you buy, they can add some horses too. The fact that SC-Project supplied the astonishing-looking titanium pipes on the factory Repsol Honda MotoGP machines doesn’t hurt the cause in my eyes either.

All SC-Project’s slip-ons are stunning looking, making it quite hard to choose one from a visual point of view—pretty much any of them would look awesome on the Kawasaki Z900.

SC-Project S1-GP Review: Sound

I searched through the Motovation Accessories website—Motovation is the official importer of SC-Project parts—and settled on the S1-GP slip-on. Handily, you can input the year, make and model of your motorcycle and limit the search results to compatible items. Helpfully, alerts you that the item is coming from Italy and may take several weeks. Fortunately, in this case, the pipe arrived very quickly— around ten days. That was a nice surprise.

I was genuinely amazed by how light the muffler felt when it arrived; it is noticeably lighter than the stock one, of course. Of course, the exquisite SC-Project workmanship did not surprise me at all. I also liked the (unexpected) pure carbon-fiber one-piece exhaust cover that replaces the two smaller ones on the Z900. As I said, the Kawasaki is a relatively simple, low-cost machine—the SC-Project slip-on and carbon cover pieces of exotica I bolted on elevated the machine’s finish. Man, this thing is pretty.

The install process is laughably simple. Once the two lower stock heat shields have been taken off, it’s a matter of just removing the one bolt where the muffler attaches to the frame, and undoing the large circular clip. Then, the S1-GP can be slipped on over the catalyst’s short pipe outlet that pokes from under the swingarm.

SC-Project S1-GP Review: MSRP

Re-using that same clip, once I’d tightened up the connection, it was then just a matter of adding the SC-Project one-piece carbon-fiber cover. I took my time, and it might have taken me as much as half an hour. If you have any level of competence, you will probably do it in about half that, I’m sure.

Firing up the Z900’s motor, the exhaust tone is barely changed. It’s a little louder when riding, especially if you’re on the gas and riding hard. The good news is, if you’re going to get nicked for something, noise won’t be it. When you blast past that radar gun, at least you won’t get a ticket for noise.

The entirely unexpected benefit of the S1-GP exhaust is in the handling department. Despite the standard muffler not being overly heavy, the S1-GP pipe is much lighter. Reducing weight hanging out far from the Z900’s center of mass makes a huge difference in how the motorcycle rides.

SC-Project S1-GP Review: Price

The bike hasn’t lost its excellent, neutral handling, though the Z900 now turns in much quicker than before. That was something I hadn’t expected, and I was delighted to experience. After that first ride, I’ve found myself absolutely loving how late I can turn-in, and how well the chassis tracks in corners at speed.

Overall, the S1-GP slip-on from SC-Project delivered in spades for me. The primary objective of improving the motorcycle’s looks was achieved easily—the Z900 looks fantastic now. The significant improvement to the machine’s turning was a surprise, as the Z900 already turns beautifully, and I’ll take it. This SC-Project S1-GP slip-on exhaust is well worth the outlay, and I’m absolutely delighted.

SC-Project S1-GP Fast Facts

  • Body and end cap: Titanium
  • Heatshield: Carbon fiber
  • Hardware: Bike-specific included

SC-Project S1-GP Price: $647 MSRP