Speed’s Secrets March 2007

Timing Is Everything

Last issue we discussed converting early Magnetti-Morelli fuel injection bodies to the later Delphi style. We talked about injector sizes and the importance of getting the right fuel curve, now we need to address the next step: matching the optimized fuel curve with an optimized ignition-advance curve. Something else to consider—this applies to bikes with carburetors as well as EFI systems.

Performance tuning an ignition system works two ways. It can spark a lazy engine to life and street-tame a highly modified one. Back in the days of points and condensers this was a straightforward job, but today’s Twin Cams are fully electronic; the ignition systems are sealed and tamper-proof. Factory-set with pre-programmed advance curves, they don’t always deliver the spark a specific engine requires, though. Add a few common modifications like a free-flow air filter and exhaust, and maybe a different set of cams and that factory advance curve is no longer close to where it should be.

Enter the aftermarket and a savvy tuner. Let’s say we’re working with a basic Stage I Kit consisting of a high-flow air filter and performance pipes, and a re-jetted carburetor or recalibrated fuel-injection system. A little work on the ignition timing can do wonders here. Those engine modifications beg for a new advance curve. Fortunately there are plenty of add-on modules available to allow just that and in these days of computerization the adjustability is almost beyond belief. Adding ignition tweaks into a Stage I mix offers easier starting, smoother running, and more horsepower and torque overall.

But properly setting that curve takes some knowledge and experience. Case in point: Say you’ve just finished fuel mapping a bike and you have an air/fuel ratio that’s near perfect, except there’s an annoying ping, say around 2800 RPM. With today’s control modules you can adjust the timing in that RPM range only. Or maybe everything’s right, except the engine’s still a little sluggish on the bottom end. To perk up throttle response the timing can be adjusted for that, as well. The beauty to all this is that you don’t have to discard a complete ignition curve that’s performing nicely everywhere else in favor of a less aggressive curve overall. All that the ignition curve really needs is a little help in one area. And it’s easy—sort of—when you have the right equipment to work with, and know what you’re doing.

The most important thing about ignition tuning, say the guys at Speed’s Performance Plus, is to start the performance curve off right, and on a fuel-injected bike that means first properly setting the throttle position plate. With the Delphi-style throttle body the idle is controlled via steps in the IAC motor; the conversion units and earlier Magnetti-Morelli systems use an adjuster screw to control the idle (similar to a carburetor), but there’s a TP (Throttle Position) switch involved, too, and its voltage must be properly adjusted. Working from there, Speed’s generally limits the ignition curve to a 6000 RPM redline. The idea is to make the power quicker and keep it lower in the RPM range where a street engine will be used most. Keeping the power in that 5000 to 6000 RPM range as a top limit greatly increases the engine’s longevity, too.

To make the necessary ignition curve changes Speed’s generally uses the Daytona Twin-Tec module on carbureted bikes and the Power Commander’s ignition function on the fuel-injected models. Both include an assortment of pre-written performance curves but those are really just starting points. Every bike is going to be different and the best-performing timing curve will vary depending on the motorcycle, the modifications made to it, its rider, the way the bike is ridden and where it’s ridden.

An ignition curve can end up being anywhere from 30-degrees to 50-degrees total advance, and how it gets there—the steps of advance and where they occur—will be equally varied depending on the bike. That’s why it’s generally money well spent to turn this job over to a pro with a dyno. Armed with the right aftermarket tuning module and a laptop computer you can experiment with ignition timing yourself, and come pretty close. But chances are you won’t come as close as someone using a dynamometer to match everything—the optimized fuel/air ratio and its corresponding ignition advance—perfectly.

What’s it going to cost? At Speed’s the bill is generally under $200 for a carbureted bike and half again as much for a fuel-injected model, plus parts. It’s a one-time expense but the benefits will be felt and enjoyed for years to come. After all, timing is everything.

Article reprinted from Iron Works Magazine, Mar. 2007

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