Testing this hot pipe on a YFZ450R

By the staff of Dirt Wheels, photos by Daniel Gonzalez

One lap on our local practice track put a smile on our test rider’s faces. The power is potent and fun to play with.


Another Yamaha YFZ450R exhaust test? You bet! Yamaha is a godsend in the sport ATV industry. They continue to produce the legendary YFZ450R, while the rest of the sport 450s have fallen off of dealer floors. That means that aside from the healthy number of Honda TRX450R projects out there, the YFZ450R is the only sport 450 we get our hands on every year to test and upgrade to our liking.

We have been on an exhaust kick lately, and Rossier Engineering is the latest one. However, this isn’t the old Rossier. The company is under new ownership, and the products are getting freshened up! We were sent their newest Rebel 4 full exhaust system for a test with our 2019 Yamaha YFZ450R.

We hadn’t heard the name Rossier in quite some time, but eventually, we saw it on social media. David Martinez-Cotton reached out to inform us that he had taken over Rossier and planned to continue and improve upon the exhausts.

The Rebel 4 full system exhaust is constructed from stainless steel and aluminum components. The muffler can is 12 inches in length with an attractive end cap. The header pipe has steps that increase in size towards the muffler in specific locations to provide the proper power increases throughout the range.

David spent many hours dyno testing to obtain what he feels will work best for the YFZ. The muffler comes in Matte Black, with three color choices for the end cap and eight color choices for the Rossier Engineering sticker.

Installation is straightforward. The old exhaust comes off and the new one takes its place. The exhaust slips together without clamps. This allows for larger-diameter exhaust tubing and decreases weight.

The Rossier weighs less than the stock system and provides far more exhaust flow. It does, however, take away the spark arrestor, which means this system is designed for closed-course riding and racing.

As with any engine, it is important to know that you will need to increase the fuel and allow more airflow through the intake to keep up with a high-performance exhaust. We installed a Vortex ECU that is adjustable and took the stock airbox lid off.

The muffler is a 12-inch -long can with a billet-aluminum end cap. The header pipe is stepped for impressive power increases through the range.


Let’s start by stating that we don’t have dyno numbers for this exhaust, but we can tell you that the increases were massive in comparison to the stock setup. The most noticeable increase was from the mid-to-top rpm range. While the YFZ just keeps pulling well past where it would fall on its face before.

Low-end torque saw benefits, and the engine is snappy and crisp. The midrange was still very usable, but if you aren’t holding on tight and riding the quad aggressively, it can get out of hand.

The sound is the second-most noticeable thing about this exhaust. It is throaty and, above all, loud. Some of our staff and testers can’t get enough of how this pipe sings, but others wanted it toned down.

However, it is an exhaust meant for aggressive riding and racing, with optimum exhaust flow for the most power output it can achieve. It won’t pass forestry decibel requirements, but a spark arrestor is in the works, and Rossier might even produce a quiet-core version.

Either way, as a closed-course exhaust, the $569 Rebel 4 was very impressive and tuned right for the Yamaha YFZ450R.


Go to, or call (970) 391-8675 to find out if they make a full system for your quad, so you can gain the benefits of the Rebel 4.

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