"Deep breathing is key to a good running Harley. It’s that first step, the biggest bang for the buck."
Okay, what’s my first step? How I do get more performance from my Harley without going broke? I want the biggest bang for the buck.
Pro bike techs hear that every day, the guys at Speed’s Performance Plus (SPP) probably hear it more than most. They travel the country setting up shop at bike events everywhere and most riders asking these questions aren’t looking to win horsepower shootouts or set Bonneville records. They just want some more oomph from their Harleys; that nice crack of acceleration when the throttle gets twisted, passing power when it’s needed, smoother running, and especially with the late-models, cooler running. And no one wants to spend a lot of money.
A tall order? Not necessarily. All of the above can be had with an economical Stage 1 tune, a session involving a little parts swapping and a re-mapped fuel curve. The results can be dramatic. On its best day a bone-stock 88-inch Twin Cam might make 59 or so horsepower with about 70 lb-ft of torque. A 96-incher will deliver a little more and those 103s and 110s just a bit more than that. In all cases though, that factory-stock bike will probably be spitting back every once in a while, noticeably surge at cruise speeds, and the late-models will typically run way too hot. Stage 1 bolt-ons along with a dyno-tune to go with them can make all that go away and bring, at a minimum, 15 percent more power to the table. The fix boils down to letting the engine breathe and giving it the added fuel it needs to match the increased airflow. And it all starts with the filter on that carburetor or throttle body.
Forget about those OE throwaway elements. What you’re looking for is something using premium gauge as the filtering medium. Not only will this do a better job of filtering, it significantly increases airflow and is reusable. And size is important. Ideally, don’t use anything smaller than a 2-3/4-inchwide filter for a stock engine. That’s the minimum, SPP’s Jamie Hanson says. Bigger is better, and Speed’s regularly mounts filters wider than even that, always set into an open-back cover. All this is nicely sized to get enough air into a TC96, 103, or 110, and more than enough for an 88. Now you have to get that air out.
A real performance exhaust is about more than just looks and sound. Here again, the guys at SPP have helped thousands of riders choose a system that’s right for them. Here’s the rundown, the pros and cons as they see it. Short, wide-open drag pipes? Most often, Wayne Hanson tells us, that’s something best reserved for high-rpm, large-displacement engines. At anything less than full-throttle these pipes can actually rob power. Large diameter pipes? Unlike air filters, bigger isn’t always better here. There’s an optimal exhaust flow for a Harley, 300 feet-per-minute. Too big of a pipe can actually restrict things by not allowing that flow to ever be reached. The general rule for street bikes is a 1-3/4-inch diameter for the head pipes. Some systems step up that diameter two, three, even four times more than the length of the pipe, but the sizes of those diameter increases and their placement is critical. Best bang for the buck? When it’s low- to mid-range performance you’re after, a 2-into-1 with a nice free-flow muffler, the SPP crew has learned, will deliver it. These collector systems do an excellent job of scavenging gasses and controlling the power-robbing exhaust pulses. Staggered duals and true duals can be efficient systems as well, but for the best performance try and find something using a cross-over connection between the pipes, in effect turning it into a 2-into-1.
Deep breathing is key to a good running Harley. It’s that first step, the biggest bang for the buck. Combined with dyno session to get the fuel flow matched with the increased airflow, or by using one of the excellent auto-tune systems on the market (or better yet, couple the two by first having a custom map written for your application and letting the auto-tune take it from there), you’ll be looking at that 15-plus percent boost in performance, at a minimum. For plenty of riders that’s more than enough. Other guys, well, they’ll want more. We’ll get into all of that in the months to come, building performance in a logical manner, always keeping an eye on the wallet in search of that biggest bang for the buck. HB
Speed’s Performance Plus
(605) 695-1401 MN
(605) 695-2272 SD
(386) 405-7898 TN