Three easy and three not-so-easy tips to help you crank up the performance on your hog
Harley-Davidson and engine performance go together like cheese curds and piping hot Milwaukee bratwurst. They’re a natural fit, folks! American V-Twin fans have enormous aftermarket support to extract extra oomph from their engines or go whole-hog with complete performance builds that won’t leave any horsepower or torque on the table. Those of the V-Twin persuasion are spoiled for riches when trying to pump up dyno figures, and with all the options out there, we’re going to discuss some easy ways and a few not-so-easy ways to add more power to your Harley-Davidson.
Here’s the deal: Motorcycle.com and its partners at Dennis Kirk do not condone circumventing emissions or noise compliance regulations. Modifying your engine, exhaust, or ECU may violate state and federal emissions laws, depending on the products you install. We strongly encourage all readers to check with local, state, and federal ordinances before modifying the engines of their street-legal motorcycles to ensure that they work within the regulatory guidelines. Now that we have that legal disclaimer out of the way, we can talk about the fun stuff – power!
1. Get Nerdy: ECU Tuning
Why is ECU tuning the first on our list? Suppose you’ve been reading MO reviews from the past couple of years. In that case, you may have noticed a growing trend of motorcycles exhibiting ECU-related power restrictions or flat spots in the powerband. Put simply, more than a few of our amazingly engineered engines are leaving performance on the table with conservative factory tunes while facing ever-stringent noise and emissions compliance rules.
Even back when we tested the 2022 Harley-Davidson Nightster, which is powered by the wholly contemporary, water-cooled Revolution Max 975T V-Twin engine, we noticed a curious dip in bottom-end performance when measured on the dyno. Whether this is due to emissions buggery or not isn’t known, but we’ll tell you whut, it isn’t ideal!
An updated flash for your ECU will typically resolve those issues by optimizing the air/fuel ratio, ignition timing, and other variables to ensure that your engine runs at peak performance at every point throughout the rpm range – no dips or flat spots, here. A new tune alone may not necessarily increase peak horsepower and torque figures. Still, it will improve throttle response, power delivery, and operating temperatures, which can be just as beneficial in some cases.
Our friends at Dennis Kirk offer several DIY tuning solutions, enabling owners to reflash their motorcycle’s ECU. Many of these systems include pre-installed fuel maps that account for various situations, such as stock motors and those with specific performance upgrades. Beyond that, owners can seek the help of a tuning professional to develop a custom fuel map on a dyno, which is then installed on your bike’s ECU.
Remember this one because we’ll be referring to it a few times throughout this article.
×PauseUnmute
Loaded: 6.85%Picture-in-PictureFullscreen
Promoted Product: Vance & Hines FP4
Get the most out of your Harley-Davidson motorcycle with the Vance & Hines FP4 fuel tuner. This plug-and-play unit allows owners unmatched fuel tuning abilities and unlocks your motorcycle’s performance potential. Vance & Hines have designed the FP4 to work C.A.N.B.U.S. Harley-Davidson models and provide a user-friendly smartphone interface (iPhone or Android) that home mechanics can easily understand. A massive library of dyno-tuned maps is available to help match a suitable tune to your build, maximizing power, improving throttle response, and much more. The FP4 is slimmer and redesigned, providing additional data logging features compared to its predecessor. Live Data logging is still offered but refined. At the same time, the all-new Performance Data features allow owners to record rides via G.P.S. and analyze all available sensor data to pinpoint performance opportunities.
The Dennis Kirk My Garage Tool will help make sure you’re always getting the correct parts for your ride.
2. Suckin’ Wind: Air Cleaners
Let’s remember the principles of how a modern 4-stroke engine works: Suck, squeeze, bang, blow. The first step in that process is “suck,” which refers to air intake. Our OEM air cleaners are sometimes a tad restrictive, hence why even factory-spec machines such as the 2024 Harley-Davidson Road Glide CVO ST and its 121ci V-Twin engine opt for a high-flow Screamin’ Eagle accessory air cleaner. The RG CVO is equipped not only with the brand’s largest standard production engine to date but also the most powerful.
A high-flow air cleaner will increase the amount of airflow through the intake system compared to standard OEM air filters. In short, you’re letting your engine breathe a little easier by allowing more air in, which can improve combustion efficiency. That alone can have positive performance impacts when trying to reach higher peak horsepower and torque goals. However, to see any actual benefit, it must be coupled with an ECU tune to capitalize on an engine that can intake air more efficiently.
3. Bolt-on Power: Exhaust
To hear an American V-Twin engine in all of its rumbly glory, then you’ll want to upgrade the exhaust with either a new set of slip-on mufflers or an unrestricted full system. Upgrading your bike’s exhaust is one of the most cost-effective ways to find additional power, and with today’s DIY tuning solutions can be done from your own garage, hence its popularity.
We can finally get to the fun stuff and discuss obtaining significant power gains without crazy investment. So, we’ve established that an optimized ECU map will smooth out power curves and make them as tractable as programming can possibly make them – check! We’ve established that high-flow air cleaners can positively impact performance by allowing more air into your engine’s intake system – also, check!
A performance exhaust often optimizes routing, allowing the engine to expel gases more efficiently and reducing excess back pressure. Whether using a slip-on exhaust or a full racing exhaust complete with headers, you modify the air/fuel ratio by allowing exhaust gases to escape the engine more efficiently. That’s the key reason any non-OEM intake or exhaust modification needs to be coupled with an ECU reflash. If you don’t, you’ll likely create a lean operating condition that will sap outright performance and eventually damage the engine.
Owners who bolt on a set of pipes, add a high-flow air cleaner, and adequately tune their motorcycles will enjoy many benefits beyond making more horsepower and torque. Yes, pumping up those peak figures is great, but the other benefits are, too. First, we’re shedding weight by ditching heavy catalysts and emissions equipment while also using pipes with superior materials (stainless steel or titanium). Of course, we’d be remiss, not to mention improved throttle response and better power distribution.
4. Size Matters: Big Bore Kits
As the saying goes, “There’s no replacement for displacement,” and if these tips didn’t tickle your fancy with possible performance gains, then you might want to look at things that are a little more involved. That said, is this one easy? Probably not. You’ll need specialized know-how and tools to pull these jobs off. But, they usually come with instructions, and we can all go to YouTube University, right? Right!
A big bore kit replaces the stock cylinder and pistons for larger diameter units, increasing the bore and the overall displacement. In addition, we usually see much higher compression ratios due to high-compression pistons and reduced head gasket thickness found in these kits. The logic is simple: A larger combustion chamber allows more air/fuel to be combusted, producing greater horsepower and torque. Again, if you’re diving into this upgrade path, then you’ll start getting into custom ECU tunes.
5. Next Step: Camshafts
Upgrading camshafts usually follows any big bore kit because it’s a great way to influence further peak power and how it is made. The camshaft profile controls your engine’s valve timing, which can profoundly impact where an engine makes most of its power. For example, aftermarket manufacturers might “degree” a camshaft profile to prioritize low-to-midrange performance, while another may offer a design providing superior horsepower at higher rpms.
Installing camshafts can be complex and takes mechanical confidence to complete correctly. However, this kind of work is often less intense on older Evolution and Twin Cam engines than the current Milwaukee-Eight and Revolution Max platforms.
6. Open Your Wallet, Bud: Engine Builds.
Oh, the cold truth is that your engine’s performance potential is limited by how deep your pockets are. At the extreme end of things, we’re talking about all the performance goodies you can muster stuffed inside a V-Twin powerplant. That means high-lift cams, big bore kits, larger throttle bodies, high-capacity lifters, superior bearings, forged high-compression pistons, CNC ported cylinder heads, upgraded fuel injectors, improved oil pumps, and of course, a full exhaust system. Costly? Yes. Easy? Absolutely not. But will it make much extra power over the stock configuring while sounding cool? Surely, and really, does your kid need a college fund? They can spend their time at a junior college while you ride in style. Owners can take an existing engine and build it up, or reach for a pre-built crate engine, such as the Screamin’ Eagle 135ci Stage IV Performance Crate Engine ($8,149.95) shown below.
American V-Twin fans are definitely spoiled regarding the options they have laid out before them, while in search of almighty horsepower. Hopefully, our dear readers have learned a few tricks and spurred a few ideas of their own because whether you’re riding an air-cooled Iron 883 or laid back on your Milwaukee-Eight-powered Street Glide, I think we can all agree that any V-Twin will benefit from a nice set of pipes thrown on it. Have any other tech questions? Leave them in the comments below.
