If you want to get rid of the somewhat janky stock air filter cage system of the 2018-2020 YZ450F, go with the Twin Air Power Flow Filter Kit. To me the Twin Air YZ450F PowerFlow kit is the best all-around filter system for the YZ450F airbox. Why? With this kit, Twin Air replaces the stock sealing ring with an anodized aluminum mounting plate, gets rid of the backfire screen for uninterrupted airflow, adds an internal filter cage (that supports a bigger air filter), and finishes it off with a CNC-machined aluminum knob to hold the filter in place. This design brings in more air volume, increased air velocity, better sealing around the edges and better throttle response/bottom end pulling power. Yes, that is right, you will notice more rpm response out of corners as well as better pulling power out of soft loamy berms.
The downside is that some dirt particles are more prone to fall into your air boot if you're not careful with removing a dirty filter. The reason why it’s more sucbseptble to dirt particles is because Twin Air doesn't incorporate the backfire screen and unless you have a super steady hand, a few pieces of dirt can get down inside your air boot. If you do find yourself in that situation simply get a shop vac (with a skinny end/attachment) and suck out any particles that have found its way inside the air boot. If you DO NOT open/twist your throttle after the particles have found its way inside the air boot, you will get nothing past the throttle body and you’re engine will not get any dirt inside of it. The Twin Air Power Flow Kit takes a little more patience when changing filters, but can add power to your YZ450F as well as create a better sealing surface.
The cost of $259.95 is on the steep side, but if adding up dollars to the horsepower increase we witnessed on the dyno (as well as felt on the track), the price tag is worth the almost one horsepower you will be gaining. One horsepower may not seem like much, but just think that some muffler systems (with a price tag of $1000.00) can’t get you one full horsepower. You can check out the Power Flow Kit over at twinair.com.
If you have any questions about this test please feel free to email me at kris@keeferinctesting.com.