Speed’s Secrets May/June 2008
Perfect Timing!
The benefits of a professional dynamometer tune and having a savvy dyno operator dial-in the air/fuel ratio to make your V-twin engine sing are well known. The guys at Speed’s Performance Plus have performed tens of thousands of these dyno-tunes over the years and the gains, as anyone who’s had a bike set up by a pro will attest, are amazing. Optimizing the fuel/air ratio and its delivery improves everything including throttle response, horsepower and torque, overall rideability and fuel mileage. And the very best way to achieve all thismdash;those “closed loop” claims of “tune while you ride” aside—comes on a dyno and at the hands of a dyno pro. There’s no magic way around it.
Want to really optimize things? Do the same for the ignition system. A dyno tune of the ignition pays big dividends, too. Older riders might remember the days of points and condensers, a time when tuning the ignition was a totally mechanical event. Initial timing was set by manually rotating a point plate, and the advance curve was effectively manipulated by bob-weights, springs of various tensions, and limiter pins. Today’s electronic motorcycle ignitions are computer controlled by on-board “black boxes,” and this change has brought ignition timing to a whole new level of sophistication. But despite what The Motor Company might want us to believe, every motorcycle isn’t created equal and one specific ignition-advance curve can’t be pre-programmed for every motorcycle on the road. Toss in a few common modifications like a free-flow air filter and exhaust, a cam change and maybe a slightly higher compression ratio, and that factory-set ignition no longer applies, at least not for peak performance. There’s no way to adjust that factory ignition module to what you need, either, and in the case of late-model Twin Cams things gets even worse. These engines use a non-adjustable crankshaft-position sensor to fire the ignition; there’s no mechanical means to adjust even the initial timing, much less the advance curve. Fortunately there are solutions, but they involve a few new parts and the skills of a good dyno operator.
On a fuel-injected bike the ignition timing and advance can be corrected using the same Power Commander that reprograms the fuel delivery. Using the PC’s ignition adjustment software, the advance curve can be manipulated to add or decrease advance where it’s needed. Working with a Power Commander, those adjustments can be made at 250 RPM increments from idle to redline. If there’s a little sluggishness or maybe a ping in one RPM range, and the fuel mixture is known to be correct, the ignition can be advanced or retarded in just that one area. On a dynamometer that change can be evaluated immediately. Without the dyno all this becomes a time-consuming trial-and-error process. The dynamometer can tell whether power has been gained or lost, where in the RPM range this happens, and then immediately provide the answers in real numbers.
With a carbureted motorcycle it’s the same story, differing only in how you get there. On a carbureted bike the fuel delivery, obviously, is adjusted with jet changes and by switching needle positions. Fine-tuning the ignition system requires a separate ignition module such as the Daytona Twin-Tec units Speed’s uses. The Twin Tec modules are direct plug-in replacements for the OE part, offering complete adjustability and custom calibration. Whether it’s a stock, mildly modified, or big-inch race engine, the ignition can be precisely adjusted to its firing. As with the Power Commander, the Twin Tec’s timing possibilities begin with a number of pre-programmed advance curves corresponding to the most popular engine displacements and modifications. Then for super-fine tuning, each of those pre-programmed advance curves can be further modified using a laptop computer and Twin Tec’s software, here again making the changes at precise intervals throughout the RPM range. On a dyno this becomes almost easy. Almost.
“And the more modified the engine becomes, the more important the ignition becomes,” says Speed’s Wayne Hanson. “Neglect fine-tuning the ignition advance and you’ll be leaving a lot of the gains from all those other parts—the pistons, the cams, the heads—on the table.” The point here is that if you don’t optimize the ignition system you’re missing out on a lot of the crispness, horsepower, torque and overall riding fun you hoped for. And unless you have a dynamometer at your disposal, and can put a load on that motorcycle to test and prove the changes you make, you’ll be shooting in the dark. Check out the Speed’s Performance Plus website for their travel schedule. They bring the dyno—and all their experience—directly to you all season long. There’s no reason to leave anything on the table when it comes to performance.
