Opening up the air box
How To Open Up The air box on The Honda CRF450X - Give It Some Room To Breathe!
Now that you have your new CRF450X, I recommend stepping back and give it some room to breathe. Literally! This bike, not unlike its smaller CRF250X cousin, has a seriously restricted intake tract. There are two quick and simple things you can do to remedy this performance robbing situation. One, install a free flowing air filter system such as the Twin Air Powerflow system or modify the stock system by removing the screen. Two, open up the air box so it can breathe! Part one of this how-to will show you how to make simple air box modifications to open up the air box. Part two will go one step further for more dramatic air box alterations and results. NOTE: The results from Part 1 were so good we did not need to open the box further. So, there is no Part 2.
Opening up the air box so it's less restrictive allows more air to flow into the carburetor. More air means you can rejet to add more fuel. More air and fuel mean more power. Isn't that why we bought the 450X...the power? Opening up the air box requires you to remove the top of the snorkel and cut open the "vents" found in the side number plates.
Instructions
1. Remove the top of the snorkel. The snorkel is located on the top of the air box. To access it, remove the seat. The top of the snorkel is made of rubber and glued to the plastic air box. You can remove it by simply pulling it off. You'll have to work at it a bit, especially around the metal strap area. The adhesive is a rubber cement type and pulling it off won't damage the rubber or the air box. This is the only part of this modification that could be reversed.
On each side of the air box you'll notice in the side number plates "cosmetic" vents. Similar vents are found in the CRF450R with the exception that they are REAL vents. This part of the air box modification requires you to cut out the air box to match these vents. Before bringing with these modifications, remove your air filter and replace it with an air box cover or something similar to prevent any plastic or debris from entering the carburetor
2. On the right side number plate, using a marker or a scratch all, trace the outline of the vent onto the air box.
3. Now remove the right side number plate. You'll see the outline of the vent you just created with the marking device.
4. Using a utility knife, or similar cutting tool, cut this area of the air box defined by your outline.
5. Reinstall the number plate and check the opening for the correct size and trim as necessary.
5.
On the left side of your number plate, where the air
filter access door is, using your cutting tool, cut
out the area within the vent as shown. You'll notice
inside the door an edge to follow.
6. Remove any pieces of plastic that dropped in the air box.
7. Reinstall your air filter and seat.
That's it! Pretty simple and yet air flow is greatly enhanced. Part two will cover the next level of air box modification which requires the removal of the air box to cut a large opening on the top. This modification would make the air flow equal to that found on the CRF450R.