CRF450L / CRF450RL Yoshimura RS-4 Exhaust: Features, Fitment and Setup

Fitment and system features

Choose our CRF450L / CRF450RL 2019–2027 application when ordering. The CRF's Only product code is 224500D320-450L, based on Yoshimura's 224500D320 system. Match the listing to your model year and tell us about any existing exhaust, intake or engine changes.

This is a full system: it includes the header, connecting pipe and muffler, along with the installation hardware specified by Yoshimura. A slip-on changes the muffler section while retaining the existing header; that is a different configuration.

• Stainless-steel header and connecting pipe: paired with an aluminum muffler and carbon-fiber end cap.
• Tucked-in header routing: helps keep the pipe less exposed to impacts.
• 18-gauge header construction: a feature of our listed system intended for off-road durability.
• Included USFS spark arrestor: supplied with this full system.
• Made in the USA: Yoshimura manufactures this exhaust in the United States.

Yoshimura also lists sound inserts for this RS-4. A sound insert and a spark arrestor serve different purposes, so check which component is installed before riding or choosing an ECU map.

Stock versus RS-4 exhaust weight

CRF's Only confirms the following comparison for the complete exhaust assemblies on this application:

The RS-4 weighs 50% less than the complete stock exhaust. That percentage applies to the exhaust assembly, not the total weight of the motorcycle. The 8 lb saving comes from the exhaust replacement; it is not a combined exhaust-and-ECU weight claim.

This makes the RS-4 a concrete weight-reduction option for a competition build. It also gives you a useful comparison when deciding how much of your budget to put toward the exhaust, engine management or other parts of the bike.

Stock ECU or Vortex?

Running the RS-4 with the stock ECU

Yes—the stock ECU is acceptable on a stock-engine CRF450L / CRF450RL receiving this full RS-4 system. A Vortex purchase is not required simply to install the exhaust. This guidance addresses that specific combination; share any additional intake or internal engine modifications with us so we can advise on the complete setup.

You can purchase the exhaust on its own and add engine management later. Always check idle after the modification and adjust it as needed.

Why we highly recommend the Vortex ECU

The Vortex X10 ECU controls fuel delivery and ignition timing, with pre-programmed maps for supported exhaust configurations. That gives you a way to match engine management to the RS-4 and choose the intended power delivery and throttle response.

For riders planning both upgrades, our Vortex X10 ECU and Yoshimura RS-4 combo brings the two core components together. Use the map sheet supplied with your ECU to select the RS-4 setting and its starting fuel trims. Describe your intake and installed exhaust insert as well; do not select a map solely from a number mentioned in a forum or video.

Already own a Vortex and plan to change from the stock exhaust to the RS-4? Review the map selection when you change the hardware. The Vortex supplied by CRF's Only comes pre-programmed with a map designed specifically for the stock exhaust, but that is the setting for the original exhaust configuration.

Our ECU-before-exhaust guide explains how to stage the upgrades. To compare Yoshimura and FMF packages, see the ECU and exhaust combo guide.

Performance and sound expectations

The RS-4 changes the exhaust system; the Vortex gives you fuel and ignition calibrations to suit supported combinations. Consider how the complete setup responds through the throttle range as well as its peak output. We do not promise a specific horsepower increase for every bike.

When comparing dyno results, look for the same motorcycle tested before and after, with the exhaust, ECU and intake changes identified. A manufacturer dyno test is measured evidence, but results from a CRF450X or a different hardware combination do not establish the gain for your CRF450L / CRF450RL.

Sound depends on the installed insert, muffler packing and test conditions. Yoshimura lists the INS-22-K sound insert and SA-04-K spark arrestor as included components for this system; the INS-13-K sound insert is optional. The sound inserts are not spark arrestors. Follow the instructions for the component you use, and check the sound limit for your competition venue rather than assuming a particular decibel figure.

Installation and maintenance

Start with the supplied instructions for your application. Yoshimura's 224500D320 instructions also identify the system components and care requirements. Have the appropriate tools and Honda service information available before removing the original exhaust.

1. Inspect the exhaust-port gasket. Replace it if needed; do not assume a new gasket is included.
2. Align the complete system. Follow the specified assembly sequence and torque values without forcing the mounting points into place.
3. Check clearance. Inspect the relationship to the bodywork, tire, suspension, swingarm and brake components. Yoshimura notes that minor side-panel trimming may be necessary.
4. Check engine setup. If fitting a Vortex, select the appropriate supplied map. TPS calibration is unnecessary if the sensor remains in its stock position. Always check idle after any modification and adjust as needed.
5. Complete the first-run checks. Check for leaks, loose hardware and contact with adjacent parts before competition use. Resolve any fault or poor running rather than continuing to ride.

For ongoing care, inspect the mounts, joints and spark arrestor, and follow the component cleaning instructions. Use mild soap for the exterior and keep solvents away from carbon fiber. Yoshimura recommends repacking at least once a year, with more frequent service depending on use. Increased noise or new rattles call for inspection.

Frequently asked questions

What model years does this RS-4 fit?

Our CRF450L / CRF450RL application covers 2019–2027. Select your model year on the product page and include any existing modifications when asking for fitment or setup help.

How much weight does the full system save?

The complete stock exhaust weighs 16 lb and the Yoshimura RS-4 weighs 8 lb, a reduction of 8 lb. These are complete-system figures confirmed by CRF's Only.

Do I have to buy a Vortex ECU with the RS-4?

No. The stock ECU is acceptable on a stock-engine CRF450L / CRF450RL with this full system. CRF's Only highly recommends the Vortex ECU for its application-specific fuel and ignition mapping.

Does it include a spark arrestor?

Yes. This system includes a USFS spark arrestor. Sound inserts are separate components with a different purpose; having a sound insert installed does not establish that a spark arrestor is fitted.

Is the exhaust street legal if I keep the stock ECU?

No. This exhaust is sold for closed-course competition only. The public-road restriction still applies with the original ECU or the included spark arrestor.

Is there a Yoshimura RS-4 application for the CRF450X?

Yes. Yoshimura also lists the 224500D320 base system for the CRF450X. Use our CRF450X RS-4 product listing to match that motorcycle's year and application. ECU selection remains model-specific; a shared exhaust part number does not establish ECU interchangeability.

What if I already have intake or engine modifications?

Send us your model year, ECU, intake parts and engine changes before choosing a setup. The stock-ECU guidance above is for a stock-engine bike receiving this exhaust; additional changes deserve a review of the full configuration.