Horsepower: Speed’s Spotlight

Playing The Numbers Game!

harley davidson dyno

Stop in and have a talk about all this with the Speed’s Performance Plus team.

Words and Photos: Joe Kress

“Quick Gains To Big Horsepower!” “Become A Dyno Shootout Winner!” We’ve seen the claims, all touting the merits of a dyno tune and the huge results you’ll reap. All “dyno proven.” The inference is clear: That dynamometer is magic, and if you’re looking for big-time horsepower and the bragging rights to go with it, you better get your bike on a dyno because that’s where it’s all going to happen.

“We hear it all the time,” says Jason Hanson, the main dyno tuner at Speed’s Performance Plus. “Riders constantly ask variations of that same question, how much horsepower are we going to find them on the dyno.” And that, he says, is exactly the wrong question to ask. The real benefits of a dyno tune, Jason explains, don’t have much, if anything, to do with that number generated at the end, with a full-throttle pull measuring just peak horsepower and torque.

“When I tell those guys we might end up with 2 horsepower more, we might end up with 20 more; no one wants to hear that,” Jason goes on. But when he explains the actual, real-world benefits of a comprehensive dyno tune, gains that’ll be felt every day and during every ride it’s as if a light bulb is switched on. The important gains found on a dyno, and they can be substantial, Jason says, will come from the power and torque found hidden down in the rpm range where actual riding is done. “And that’s well below that wide-open-throttle peak.” Gains at the top-end? That’ll probably be there, too, but that’s just icing on the cake.

Far from being some magical device, the dynamometer is just a tool. And like any other tool, wrench, screwdriver, or hammer, it’s only going to be as good, and useful, as the guy handling it. “With today’s fuel-injected Harleys,” Jason remarks, “and with those Dynojet Power Commanders, Power Visions, and Auto Tunes there’s so much that can be done on that dyno to optimize overall performance and power delivery.” And it’s that power delivery, where in the rpm range the useful power is made, that’s key. That’s where a dyno with a knowledgeable, experienced operator at the controls comes in. It doesn’t take any special skills to lash a bike onto the rollers and whack the throttle open a few times; making the most of that session, bringing out everything that bike has in it throughout the rpm range, off-idle to that WFO position, is another matter entirely.

“First off,” Jason explains, “you have to know where you are before you can map out a plan to get where you want to be.” Most often, he says, an untuned bike will show an air/fuel ratio that’s all over the place; rich where it should be lean, lean where it should be rich. All adding up to a bike barely performing to its potential, much less producing those peak numbers everyone’s so interested in. What’s too lean and what’s too rich? The exact numbers vary, Jason says, no two bikes being identical, but anything approaching a 15:1 air/fuel ratio (AFR) is too lean. And with late-model Harleys that’s not uncommon, a direct cause of all manner of performance complaints ranging from surging at cruise to that hot-running condition everyone agonizes over.

What’s optimum? Here again, Jason related, that depends on the bike itself; one with 2,500 miles on it will call for something different than an outwardly identical bike with 25,000 miles showing. And this is where that operator know-how and experience comes in. Rule of thumb: a 13.4 to 13.9:1 AFR, or thereabouts, is what Jason’s found most useful for every day riding. And since everyday riding doesn’t happen at wide-open throttle, those optimum AFRs and the ignition timing to go with them will be meticulously adjusted, adding or taking away fuel and spark advance at every 250-rpm increment from idle to the 5,000 or 5,500 top limit SPP likes to use. And that’s done at all throttle positions, closed to wide open. For the part-throttle cruising ranges, say 2,000 to 3,500 rpm, the air/fuel ratio will be set for the best compromise between power, cool running, and acceptable fuel mileage. At 40- to 60-percent throttle positions the mixture might be set a little richer for passing power, and with the throttle cracked wide open, the AFR will be set at its richest. “It’s almost like setting that engine exactly where it wants to be for every mph in every gear,” he says.

Will all this produce that “Dyno Shootout Winner”? Probably not. But it’s a safe bet that when it comes to all-around power and everyday rideability, any bike set for peak horsepower only won’t hold a candle to one that has been dyno tuned the right way. Stop in and have a talk about all this with the Speed’s Performance Plus team.

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Speed’s Performance Plus

(605) 695-1401 – MN

(605) 695-2272 – SD