If you don’t think that drilling holes in your 2019 airbox cover is a good idea—Husqvarna opened up the 2020 Husqvarna airbox with vents.


Dear MXA,
How do I fix the airbox on my 2019 Husqvarna FC450? Do I drill holes in the number plate? What else should I consider?

The 2019 Husqvarna FC450 is choked down on both ends of the system. The 2019 Husqvarna airbox design suffocates the throttle response of the engine. It runs like it has a rag in the airbox at low rpm. To prove the point, MXA ran our 2019 Husky FC450 on the dyno and on the track with the airbox cover off. On the dyno, horsepower jumped from 56.40 with the stock airbox cover to 57.50 with no airbox cover. On the track, every test rider was impressed with the snappier throttle response and quicker pick-up of the opened-up airbox.

On the opposite end of the spectrum from the airbox, the muffler is also a hindrance to responsive power output. The stock FC450 muffler is very good in the AMA/FIM sound test, but it achieves these low decibel numbers by having an ice cream cone-shaped restrictor in the perf core. The metal cone kills throttle response at low rpm and contributes to the 2019 Husky FC450 being 1 horsepower down to an unrestricted muffler.

The 2020 KTM airbox has more many more and much larger holes than the 2020 Husqvarna, plus they are placed in the correct location. The difference in throttle response is noticeable.

The airbox solution. Drill 1-1/4-inch holes in the air box cover. We asked the Rockstar Husqvarna team where to drill the holes, and they said to make sure that all of the holes were located behind the air filter—not next to it. Additionally, we drill into the plastic subframe behind the extended airbox cover where the hollow section leads to the airbox space. Next, remove the side panels that cover the other side of the airbox and you will find that Husqvarna molded a hole into the right side of the airbox; however, they put lips on the side panel to seal up this air vent. You should locate exactly where the molded opening is and drill a hole through the side panel to line up with the airbox opening to let air in.

The muffler solution. Any aftermarket slip-on muffler will solve the problems caused by the restrictor in the stock muffler. Or, if you know someone who installed an FMF or Pro Circuit exhaust system on their FC250, see if they will sell you their stock FC250 muffler. It is identical to the FC450 muffler but does not have a restrictor in it.

This how MXA drilled our 2019 KTM airbox cover.

A few more suggestions. (1) Swap the long-throw throttle cam for the optional quick-turn throttle cam. This will speed up how quickly the power comes on by lessening the degrees of rotation needed to get to 100 percent power. (2) Run the map selector switch on ″2.″ This is the aggressive map, which doesn’t make more horsepower but is noticeably crisper. (3) Add one tooth to the rear sprocket. This will perk up low-end acceleration and allow you to get to third gear sooner.

The 2020 Husqvarna already has holes, more like slot, in the airbox cover, but they aren’t big enough. We still drill the 2020 FC450 airbox cover,  change the gearing and run a straight through muffler on our 2020.


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