Looking at a stock Harley-Davidson’s air-filter setup, it’s a wonder the bike runs at all. Talk about restricted! The small size and the density of that OE filter element is bad enough, but couple that with the tiny openings in the housings to let air in and it’s a surprise the engine can breathe deep enough to get the bike much past a walking speed.
Okay, that’s an exaggeration. But it doesn’t alter the fact that a Harley can stand some help in the air-filtering area. Reduced to the basics that a V-twin is a big air pump and the more air it can take in the better it’ll perform, a free-breathing engine responds to the throttle better, it’s crisper overall and it’ll even deliver better fuel mileage. Now, in fairness to The Motor Company, it’s handcuffed by stacks of governmental regulations when choosing its parts and systems. Emission regs and, more to the point here, sound restrictions dictate the OE air filter/air box choice. A deep-breathing intake can get a little noisy and, cutting decibels where they can, concessions are made.
Get that motorcycle off the showroom floor, though, and you can unlock those handcuffs and let that bike take its first deep breath. “Swapping on a new air filter and backing plate,” says Jamie Hanson, the tuning ace at Speed’s Performance Plus (SPP), “is just about the first thing we’ll do to any Harley. You have to get the air in and then get it out with a good exhaust.” And while those two, intake and exhaust, most definitely go hand-in-hand, let’s concentrate on the intake side of things for now.
Bigger is better, of course, which is why SPP spec’d out its own proprietary filter element.
Forget about any of those throwaway paper or foam air-filter elements. They won’t let in enough air when they’re new and they’re prone to clogging pretty quickly making matters even worse. What you’re looking for is a pleated element using some sort of premium gauze as the filtering medium, multiple layers of it pleated, folded, and sandwiched between wire mesh. Not only does this do a better job of filtering, it significantly increases the airflow. And it’s reusable. You can clean it over and over again. K&N immediately comes to mind. Its filters have been a performance mainstay since the ’60s and it’s standard-equipment in lots of aftermarket filter kits. But size is important, too, which is why SPP, after tuning literally thousands of Harleys, has come up with its own version of that pleated-gauze filter. “And ideally,” says Jason Hanson, Jamie’s brother and the dyno wiz at SPP, “for a stock engine, nothing smaller than a 2-3/4-inch wide filter should be fit. That’s the minimum it takes to move enough air.” Bigger is better, of course, which is why SPP spec’d out its own proprietary filter element. Pleated gauze, it’s a full 5/8-inch deeper than anything else on the market and part of its “Speedy Flow” air filter kit. This high-flow package includes it all. Unlike the confining OE setup, that bigger free-breathing filter is used with an open-back cover and the kit’s billet aluminum backing plate has a unique internal breathing system. There are high-temperature Viton O-rings too, eliminating oil leaks, and locking tabs keep all the mounting hardware from working loose. The kit even accepts Speed’s One-Way Crank Vents, good for another 3 to 5 mpg and easier running. Most of these bolt-on filter/backing plate upgrades, the Speedy Flow included, let you keep the OE cover or use most any aftermarket cover you choose.
Like the forward-facing “ram air” look? There are plenty of deep-breathing options there, as well. One good example is the S&S Single Bore Tuned Induction System. This one uses two conical filter elements, more than doubling the filtering area of a stock Harley intake system. And it looks really cool in certain applications. Now, if you’re wondering about the payoff for all of this, here’s the bottom line. With either one of those choices, a new free-flow filter mounted in an open-back housing or with one of those forward-facing setups, when combined with a good exhaust to get that extra air out and some re-jetting/re-mapping to properly balance the air/fuel ratio, you can be looking at up to a 15-percent boost in overall performance and ridability. And that’s a situation a whole lot more appealing than that restricted OE filter system you started with. HB
Track down SPP at these upcoming events:
• Myrtle Beach Bike Week May 18-28
• Laconia June 8-17
Speed’s Performance Plus
(605) 695-1401 – MN
(605) 695-2272 – SD