We wanted to find the missing horsepower we kept hearing about, so we searched high and low through the chrome hills of V-Twin cylinder-land (also known as our stock '07 Road Glide), but not a lot was found. So the quest was on-we decided to try a different tack; if we could feed the bike more air and fuel, could we find more power? If something as simple as an air filter was a way to find more horsepower, we wanted to see for ourselves. The Arlen Ness Big Sucker air filter and backing-plate kit was a good place to start. For a retail cost of around $120, the air filter can be cleaned and reused (not a one-time use), so it seemed like a good deal. Now we just needed to see about that missing power. We stopped at Horn Cycle Works in Pomona, CA, to install the air-filter kit and test it out on the dyno.
The owner, Curtis Horn, got started by strapping the bike on the dyno and doing a few safety checks on things such as tire air pressure and oil levels, then got some base numbers on the bike. It put out around 58.3 hp and 72.9 lb-ft of torque, just about what we expected from a California ride.
This is the Arlen Ness Big Sucker kit: one high-flow air filter, one replacement backing plate, new gaskets, and hardware. With this kit you'll need to use the stock filter cover. Ness offers a few covers to choose from if you prefer, but we wanted to keep the cost down. | 
We got started by removing the stock air-filter cover, stock filter, and backing plate. | 
The first thing you can see is how much bigger the Ness filter (left) is. |
Next, new O-ring breather gaskets were placed onto the Ness backing plate, along with a new EFI gasket. A small dab of 575 sealant kept them in place 'til the backing plate was tightened down. | 
Two different-sized head breather bolts come in the kit, so check to see which size is correct for the year and model of your bike. | 
With the backing plate in place, the filter's mounting bolts were installed with a small amount of blue threadlocker. |
Then the Ness Big Sucker air filter was installed with the stock air-filter cover. |  |  |