The Diagnostic Checkup

Speed's Spotlight

harley tune up speeds performance plus

How Speed's Performance Plus gets the most from an auto-tuner.

Words and Photos: Joe Kress

Most everyone is aware of the need for an FI remap on a Harley. It’ll dramatically sweeten the performance of a stock bike, and when you’ve added a free-flowing exhaust, a good air filter, and maybe some aggressive cams to a V-twin, that remap becomes mandatory. That’s why the aftermarket is filled with fuel-management modules and systems all aimed at supplying that necessary computer remap and making it an easy at-home deal. It’s big business and if we’re to believe the claims all you have to do is install these electrical wonders and go for a ride. Presto, the bike automatically recalibrates itself to fuel-delivery perfection, new exhaust, air filter, and cams taken into account.

Sounds great, and for the most part it is. Or it can be. “Those auto-tunes really do work,” says Jamie Hanson of Speed’s Performance Plus. “To a point.” Tuning specialists, the SPP techs, have found that to perform their best an auto-tune system really needs a full, custom remapping first. A contradiction? Isn’t that auto-tune system supposed to eliminate the need for a custom dyno session? Not entirely, say the guys at Speed’s. Their preferred method, and one that’s made countless riders happy, is to use auto-tune as an add-on, a supplement to the kind of custom dyno tune they’ve done for years. The reasoning: auto-tune systems, and their sensors, perform best within a finite parameter, making relatively small adjustments to the air/fuel ratio. “So we’ll begin by tuning the bike perfectly on the dyno,” Jamie goes on to explain. “Once we have that custom map as a base we’ll turn on the auto-tune unit and let it keep that custom tune wherever the bike might go. It’s a procedure we’ve found to work a lot better than just asking an auto-tune to adapt to some pretty big changes.”

But what about all those “pre-written” base maps available with the auto-tune systems? The ones you download from the internet? They’ll list the year and model of a particular fuel-injected Harley, and if you scroll through the library you might find a map not only based on your particular bike but your bike with the same aftermarket pipes and air filter you’ve installed—and if you’re lucky even the cams you might have added. Won’t that take the place of a custom dyno tune as the starting point for an auto-tune? “Let’s think about that for a minute,” Jamie warns. “Good as they are, a pre-written base map, even taking into account all the extra equipment that might be on the bike, can never be absolutely correct for every particular motorcycle. No two motorcycles are ever exactly identical. Their engines are made from different batches of metal that might expand and contract differently, the mileage and wear rates are different, that pre-written map might have been developed on a brand-new bike where yours has 25,000 miles on it—there’s just a host of differences, big and small, between two seemingly identical bikes. That’s why we’ve found that a custom dyno tune and a base map written for one specific bike, and that bike exclusively, is so important. It’ll be perfect, not just close.”

An example of this, Jamie says, happened at just the last event the SPP team went to. A rider came in with what he considered to be a pretty good-running bike. He’d installed an auto-tune system with a pre-written map under it. “And when we put that bike on the dyno and hooked up all the analyzers, that guy couldn’t have been more surprised,” Jamie says. “His setup was all over the place.” After building a custom map for that bike, the result was even more surprising, 8 more horsepower, 8 more pound-feet of torque, and most importantly a seat-of-the-pants all-around feel with a night-and-day improvement. “And this guy thought he already had a pretty good-running bike,” he says. That’s the difference between a custom map and a generic map as the starting point.

Takeaway here? Auto-tune systems are an electro/mechanical marvel, and when it comes to that final fine-tune they’re hard to beat. But consider turning your bike over to a professional tuner for a diagnostic dyno pull first, especially if you’ve downloaded a custom map from the internet. Think of it as a trip to the doctor for a checkup. All might be well, but then again maybe not. “And honestly,” Jamie ends, “easily 90 percent of those bikes in for a diagnostic dyno pull really need to be tuned. Some might not be too bad, but they’re not perfect. And rare indeed is the bike with a tune-up that’s right on the nuts. It does happen but not often.” Something to think about.

Contact/Source: Speed’s Performance Plus

(605) 695-1401 – MN

(605) 695-2272 – SD