If you're looking to squeeze more power out of your Milwaukee-Eight, the s&s stealth air cleaner m8 is usually one of the first mods people recommend, and for good reason. It's one of those rare upgrades that actually delivers on its promises without making your bike look like a science project gone wrong. When Harley released the M8 engine, everyone realized pretty quickly that while it's a powerhouse, it's also a bit choked up from the factory. It wants to breathe, but the stock air box is a bit like trying to run a marathon while breathing through a cocktail straw.
I've spent a lot of time around these engines, and the thing about the S&S Stealth setup is how it balances performance with a low-profile aesthetic. Some guys love the massive "look at me" air intakes that stick out six inches from the side of the bike, but if you're into a cleaner, more streamlined look, this is the way to go. It's called "Stealth" because you can actually run it under your stock Harley air cleaner cover. It's the ultimate sleeper mod.
The Secret Sauce: The Stinger Cone
What sets the s&s stealth air cleaner m8 apart from the cheap knock-offs you see online is the internal design. If you take the cover off, you'll see a little plastic or aluminum cone sitting right in the center. S&S calls this the "stinger" cone. It's not just there for decoration; it's designed to direct air smoothly into the throat of the throttle body.
In a standard air cleaner, the air comes in and just kind of tumbles around, creating turbulence. Turbulence is the enemy of horsepower. The stinger cone acts like a traffic cop, smoothing out the airflow and speeding it up as it enters the intake. This results in much better throttle response. You'll notice it most when you're pulling away from a stoplight or trying to pass a semi-truck on the highway. The lag is gone, and the bike just feels more "snappy."
Performance Gains You Can Actually Feel
Let's talk about numbers for a second, because that's why we're all here. Installing an s&s stealth air cleaner m8 on a stock bike usually results in a noticeable jump in both horsepower and torque. We aren't talking about doubling your power—let's be realistic—but you're looking at a solid 5% to 10% increase depending on what else you've done to the bike.
The M8 engine is especially sensitive to intake and exhaust changes. If you've already put a set of slip-on mufflers on your bike, you're only halfway there. You've opened up the exit, but you haven't opened up the entrance. Adding the Stealth air cleaner completes that "Stage 1" upgrade. To get the most out of it, you'll definitely want to use a tuner to recalibrate the fuel map. Since you're shoving more air in, you need to add more fuel to keep things balanced. If you don't, the bike might run a bit lean and hot, which is the last thing you want for a big-inch V-twin.
Keeping the Stock Look (Or Not)
One of the coolest features of the s&s stealth air cleaner m8 is its versatility regarding covers. Like I mentioned earlier, you can bolt your factory "football" or "lollipop" cover right onto this kit. This is a huge win for guys who like the classic Harley-Davidson look but want the modern S&S performance. Most people walking by your bike won't even know it's modified until you twist the throttle.
However, if you want people to know you've got some high-performance hardware under the tank, S&S offers a bunch of custom covers. They have the "Air 1" cover, the "Muscle" cover, and even some minimalist "Bobber" style covers that leave the filter element exposed. It's nice to have the choice. You can start with the stock cover and, if you get bored a year later, just swap the cover without having to buy a whole new intake system.
Dealing with the Infamous M8 Oil Blow-By
If you've owned an M8 for more than a week, you've probably heard about the "oil blow-by" issue. Because of how the breathers are designed, oil mist from the crankcase sometimes gets sucked into the intake, which can lead to a messy air filter or even carbon buildup on your pistons.
S&S designed the s&s stealth air cleaner m8 with a pretty robust backing plate that helps manage this better than the stock plastic unit. The hoses and channels are laid out in a way that minimizes the "dripping" effect. It's not a 100% cure for every bike (some M8s just breathe heavier than others), but it's a massive improvement over the OEM setup. It keeps the intake tract cleaner, which means your engine stays healthier over the long haul.
Installation: A Saturday Afternoon Project
You don't need to be a master mechanic to install the s&s stealth air cleaner m8. Honestly, if you can turn a wrench and follow some basic instructions, you can get this done in about 45 minutes in your garage.
The kit comes with everything you need: the backing plate, the high-flow filter element, the stinger cone, and all the necessary hardware. The instructions are usually pretty clear, but there are a million YouTube videos if you get stuck. The main thing is to make sure you don't over-tighten the breather bolts. Those go into the cylinder heads, and you really don't want to strip those threads. Use a little blue Loctite where recommended, and you're golden.
One thing I always tell people is to make sure your hands are clean when you handle the filter element. It's pre-oiled from the factory, and you don't want to get grease or dirt all over it before it even gets on the bike.
Maintenance and Longevity
The filter that comes with the s&s stealth air cleaner m8 is a pleated gauze material, similar to what you'd see from K&N. The best part? It's washable. You don't have to keep buying new filters every time you do an oil change. You just buy a cleaning kit, wash out the gunk, let it dry, re-oil it, and you're back in business.
It's built to last. The backing plate is usually made of high-quality cast aluminum (not flimsy plastic), so it won't warp or crack over time due to engine heat. I've seen these units with 50,000 miles on them that still look and perform like they did on day one. It's a "buy once, cry once" kind of part.
The Sound Difference
It's subtle, but you'll definitely hear a difference once the s&s stealth air cleaner m8 is installed. When you're idling, it's not very noticeable. But when you whack the throttle open, you'll hear a deep, throaty "sucking" sound from the right side of the bike. It sounds powerful. It gives the engine a more mechanical, aggressive character that the stock air box hides.
Some people worry that an open intake will be too loud or "whistle," but the Stealth kit is pretty well-behaved. Since it's tucked in and has that stinger cone to smooth the air, you don't get that annoying high-pitched whistling that some of the cheaper "velocity stack" style intakes produce.
Is It Worth the Money?
In the world of Harley mods, you can spend thousands of dollars very quickly. Compared to a full exhaust system or a cam chest upgrade, the s&s stealth air cleaner m8 is actually a pretty affordable bang-for-your-buck modification. It's the foundation for any other engine work you plan to do. Even if you never touch the cams or the heads, just letting the engine breathe better makes the bike more fun to ride.
It's hard to find a downside. It looks good, it's easy to install, it's made in the USA by a company that's been around forever, and it actually makes the bike faster. If you're tired of your M8 feeling a little "tame" or "restricted," this is probably the best first step you can take. Whether you're cruising across the state or just hitting the local bike night, it's an upgrade you'll appreciate every time you twist the grip.