I recently purchased a 2009 Ultra Classic Electra Glide, which was completely stock. After being blown away off the line last week by my friend riding a Road King with some aftermarket parts I decided that I needed to make some adjustments. After doing some research I found out that the two things I can do to significantly up my game at a very reasonable price is to replace the air filter and get some new slip on mufflers. My first stop was the air filter. What an incredible difference!! Before adding the air filter when I cranked it up the engine seemed to build up RPM's and I had to wait for it to happen. Now when I crank it there's a nice "snap" of acceleration which is exactly what I was looking for. I'm not falling off the back of the motorcycle, but neither am I waiting for the engine to catch up with what I want the bike to do. It does what a I want, when I want. The need to downshift to do things like climb hills or pass on the freeway has diminished, I can do both in 6th gear if I want to. I climbed a nice steep hill yesterday doing about 40 mph in sixth gear. It rumbled nicely, the engine shook just like it's supposed to, and I smiled from ear to ear. No downshift required, just all American Milwaukee muscle showing off. When I do decide to downshift and get on it, it performs exactly the way I want. It rocks. The sound is great. Much better than it was before. It's never uncomfortably loud like straight pipes It seems to have three levels of sound. When you're not getting on it, it burbles nicely like a Harley Davidson should. I can get in and out of the subdivision without causing a mutiny amongst my neighbors. When I get it on it halfway, it rumbles nicely and people know you're coming. When I get all the way on it, it roars. There is no mistaking that a Harley Davidson is making it's presence known and announcing itself with authority. I came up behind somebody on the freeway doing around 75, hammered the throttle a couple of times in 5th gear to feel the snap, and they promptly moved out of the fast lane so that I could pass, and this was a guy in a big four wheel drive pickup down here in Atlanta, not some grandmother driving an '86 Buick. People not only know you're there, but you have made your presence known and they are paying attention. I love the way it sounds. I can come into the neighborhood late at night, put it in third gear and do about 20 through the suburb and not disturb my neighbors, and I can also jump on it and people stop and stare. I love this air filter. The performance is an incredible enhancement for the money, the sound is awesome, and installation is simplicity itself. S&S even has a video on YouTube that lasts for a little under 10 minutes that walks you through step by step. Just search on "s and s cycles stealth install" and there is a video from about two years ago that has been watched over 28,000 times that makes it incredibly easy to install. I've never done any work on my car or motorcycle, but I was able to take my laptop out to the garage and step through the installation one step at a time, and in less than an hour (20 minutes if you know what you're doing and have the tools handy) I had it installed and rocking down the highway. If you want it fits under the stock HD air filter cover so you can "stealth" it as the name implies, or S&S has aftermarket covers that are also available. I stuck with the stock cover, but I think I'm going to go with the aftermarket stainless, it looks pretty cool and makes it stand out without being obnoxious (I'm trying to do the whole "adult ridden Harley" thing, although at 45 it could be argued that I'm not really succeeding, but that's ok :-) ). I had to make some runs to Home Depot to purchase some tools at one point, but they were small hand tools, I spent less than $25. All in all I highly, highly recommend this air filter, I am one happy guy being a good neighbor while at the same time rocking a legend on the highway just as loud as I want. I can't wait to put my Vance and Hines pipes on today. I'll update this and tie the two reviews together when I'm done.