I spent several months riding with the 87 Octane Stock Improved ECU flash from 550Performance before stepping up to the 91 Octane Stock Improved version. I wanted enough seat time with that 0.5 horsepower, ECU-only increase before deciding on the next step for the Ultimate Motorcycling Honda CRF300L Rally Project Bike.

The Rally is a fun motorcycle right off the showroom floor. However, depending on how you use it, you can improve its performance without losing the character that makes the bike appealing in the first place.

If you weigh 160 pounds, commute during the week at 50 mph, and spend weekends cruising graded forest roads, the stock Rally will probably do everything you ask of it. However, if you weigh more than 160 pounds, carry tools and spares in soft luggage, ride with impatient friends on 700cc and 1200cc ADV bikes, and regularly travel between one and five freeway hours before the dirt even begins, you will likely start looking for more power. That is where spending about $355 —send-in ECU flash plus the intake parts — and a Saturday in the garage with 550Performance starts to make sense.

Highway climbing: stock vs 87 vs 91 Octane

I live near Mt. Hood in Oregon. The highway climb toward the mountain includes several miles of sustained 6% grade rising to roughly 4400 feet of elevation. With the stock ECU, the Rally needed to be near redline in 4th gear just to hold 45 mph in a 55 mph zone. The 87 Octane Stock Improved flash allowed the bike to maintain 55 mph in 5th gear. After adding the airbox modifications and upgrading to the 91 Octane Stock Improved flash, the Rally now pulls 65 mph uphill in 5th gear between 3000 and 4400 feet of elevation.

How much power the 91 Octane Stock Improved adds

The 91 Octane setup adds 2.6 horsepower and 0.8 lb-ft of torque over stock on 550Performance’s dyno, not Honda’s brochure figures. That is the 11% horsepower and 5% torque gain 550 lists for Stock Improved. The earlier 0.5 horsepower bump was the 87 Octane flash with a stock intake; the 11% figure is the 91 package with the airbox work. On a 286cc engine, those percentages are modest on paper. From the saddle, they feel like more.

I also changed the rear sprocket from the stock 40-tooth to a JT Sprockets 42T. That gearing change lets the bike comfortably maintain 65 mph in 6th gear instead of downshifting to 5th on the mountain. Combined with the 91 Octane tune, the difference in overall rideability is substantial.

H2 Installing the 550Performance airbox and ECU flash

The complete package requires replacing the airbox snorkel, velocity stack tube, airbox lid, air filter, and re-flashing the ECU. Because the airbox sits deep in the center of the motorcycle, access takes time. The project took about eight hours from start to finish. At one point, my garage floor looked like a yard sale.

Part of the installation involves enlarging the snorkel opening and sealing both the snorkel and velocity stack in place with permanent adhesive caulk. The sealant needs roughly 24 hours to cure, so I purchased a second airbox for about $35. That let me prepare the modified unit ahead of time and finish the installation in one day.

The only part that slowed me down was disconnecting some of the connectors beneath the fuel tank. Fellow owners guided me through the process.

To its credit, 550Performance includes a thorough instruction manual, and the step-by-step process was easy to follow. It also includes cutting templates and tips, such as heating the parts with boiling water or a hair dryer to make installation easier.

On the trail and on the street

Once installed, there is nothing left to do except ride the upgraded Honda CRF300L Rally. The additional power is immediately noticeable from idle to highway speeds. Off-road, the broader power delivery allows me to stay in one gear much longer than before. At an average trail pace around 30 mph, 3rd gear now handles everything from slower technical terrain to open sections without constant shifting. 4th gear has become equally versatile, pulling smoothly out of tight turns and climbing hills without demanding a downshift.

One side effect of the freer-flowing intake setup is significantly more intake noise during acceleration. The replacement airbox lid is largely covered in FrogzSkin mesh. It does an effective job of keeping dirt and water out while allowing much more intake sound to reach the rider.

The payoff for all of these changes is noticeable when riding with my impatient friends. I can now comfortably keep pace with a Yamaha Ténéré 700 and Triumph Tiger 1200 on mixed-terrain rides. Before the final 550Performance upgrades, my riding buddies frequently had to slow down and wait for the Rally to catch back up. That no longer happens, on road or off.

Is the 91 Octane Stock Improved worth it?

The CRF300L Rally is certainly not a high-horsepower motorcycle, and this package does not try to turn it into one. Riders chasing 35 horsepower builds can certainly go much farther into 550Performance engine modifications. At that point, I would simply choose a different motorcycle.

The 91 Octane Stock Improved 550Performance upgrade makes the Rally stronger where it matters most: carrying more weight, climbing elevation, surviving freeway rides, and keeping momentum in the dirt. For riders who already love the CRF300L Rally but want more usable performance without sacrificing its lightweight nature, the difference is undeniable.

550Performance notes that its ECU modifications are “for closed-course competition use only, not intended for street use, and not legal for sale or use on pollution-controlled motor vehicles.” We trust you will do the right thing.