No doubt you’ve seen, or more likely heard, a motorcycle being dyno tuned. That term itself—dyno tuned—has magic to it, and more than a little mystery. What’s really going on? The motorcycle’s roaring, the dyno operator’s intently staring at a computer screen, tapping away at a keyboard. What exactly is happening, and what, if anything, are the benefits? Well, a lot is happening and the benefits can be phenomenal and immediately felt once that bike is rolled off the dyno and handed back to its owner.
The simplest explanation that Jason Hanson, who runs the dyno at Speed’s Performance Plus and who learned the tuning art from his father, master-tuner Wayne Hanson, can offer is that to make any bike run its best, whether it’s stock and especially when some parts have been changed, that bike must be tuned as a unique package, and no two bikes are ever exactly the same. A Road King with 2,500 miles on it will have significantly different tuning requirements than would a seemingly identical bike with 25,000 miles on it. That’s where the dynamometer comes in.
A sophisticated piece of computerized testing equipment, a dyno simulates actual on-the-road riding conditions. All the tuning it allows—the precise adjustment of the fuel delivery and ignition timing—will be specific to the bike being tuned. And it all happens “live.” On modern fuel-injected motorcycles, and with the aid of add-on modules and software such as the Power Commander V that SPP most often uses, the result will be a tuning accuracy only dreamed of a few years ago.
The first step is an information-gathering base run: determining exactly how that particular motorcycle is running and where it’s rich and where it’s lean. The setup involves strapping the bike onto the dynamometer and its drum, making all the necessary electrical connections between the dyno’s computer and the the bike, then inserting an exhaust-gas analyzer (sniffer) into the exhaust pipe. The motorcycle is fired up and, for all intents and purposes, driven down the road. “And more often than not, that initial evaluation will be all over the place,” Jason explains. “The bike will be rich where it should be lean, lean where it should be rich.” With information gathered from that base run, the dyno operator begins making corrections.
A sophisticated piece of computerized testing equipment, a dyno simulates actual on-the-road riding conditions.
What’s lean and what’s rich? The exact numbers will vary once again depending on the motorcycle, but generally speaking anything approaching a 15.0 to 1 air/fuel ratio (AFR) is too lean, and with the newer Harley-Davidsons, that’s not uncommon, a direct cause of the hot-running condition riders complain about. Contrast that with the 13.4 to 13.9 to 1 AFR, or thereabouts, that SPP’s found most useful for everyday riding. And on the dyno, these adjustments can be precisely set, adding or taking away fuel at every 250 rpm step (“cells,” they’re called) from idle to the 5,000 or 5,500 rpm limit SPP likes to use, and at all throttle positions, closed to wide open. The tuning is so accurate you can darn near set the air/fuel ratio exactly where it needs to be for every mile per hour in every gear.
Without turning this into a dyno-operator’s manual, here’s how SPP achieves that accuracy. Starting from 0 percent throttle to 5 percent throttle opening, they’ll do what’s called a “steady state motion” tune. The motorcycle will be held precisely at 1 rpm with the throttle at one specific degree of opening while the air/fuel ratio is manipulated right there. Next, they’ll do “roll on” tunes using the dyno’s Eddy Current Brake to add resistance and simulate riding conditions as they go to 10 percent throttle, 15 percent, 20, 40, 60, 80, and finally 100 percent throttle. For the cruising ranges, approximately 2,000 to 3,500 rpm, the air/fuel ratio can be set anywhere from 13.4 to 13.9, a compromise between power, cool running, and acceptable fuel mileage. At 40 to 60 percent throttle, the mixture might be set a little richer than the cruising ranges for passing power a bit richer still. Crack that throttle wide open and the AFR will be set at its richest. The whole procedure can take an hour or more to complete, and with the latest tuning equipment and an operator’s skill, a Harley-Davidson’s cylinders can each be tuned individually as well. Generally speaking, that rear cylinder might be set a little richer to keep it cooler, but here again it’s an individual consideration. A good dyno tune can address any number of other maladies, as well: deceleration popping being just one, that annoying cackle as you let off the throttle.
And as if all this isn’t enough, the dyno tune can also adjust the ignition timing with the same precision, custom-adjusting the ignition advance degree by degree in those same 250-rpm increments. The rev-limiter can be adjusted either up or down, an “accelerator pump” feature can be added, and for good measure, an “auto tune” can be turned on that will continue to keep that now-finely-tuned motorcycle running its best.
All this ends with a final torque and horsepower pull with a printed-out chart showing the results. But done properly, a dyno tune isn’t about just those numbers. It’s about what happens between those numbers, and how that motorcycle runs and rides from idle on up. HB
Speed’s Performance Plus**
(605) 695-1401 | (386) 405-7898