Let’s get one thing cleared up right here and now: “Stages” of modification to stock Harley-Davidsons are about efficiency, not inches! The fundamental issue with all new Harleys out of the box is that they don’t breathe efficiently, and there is a good reason for this: They have to meet all current regulations for emissions, and for noise. That stockers can’t breathe efficiently doesn’t mean they can’t breathe at all, and I predict increasing numbers of new Harleys will remain in their stock trim longer because the available power is actually enough for a lot of people. But beyond that, the perceived rewards of modifying the stocker are tantalizingly close for those who are prepared to dig their hand in their pocket for the most basic of tweaks: the Stage One.

Stage One
You can spot a Stage One bike very easily indeed: The air filter isn’t sunk into the plastic molding that fills the gap between the air filter cover and the motor. It’s the tip of the iceberg, but it is the most visible part. Stage One engines by definition have no internal mechanical modifications. All you are initially doing is changing the means of getting the fuel in and the exhaust gases out, but they can include ignition mods if you’re feeling flush. You can go where you want for the stuff you use, but the most common basis for a Stage One is a Screamin’ Eagle High Flow Air Cleaner kit and a pair of slip-on mufflers.

Having let the air flow more freely, it’s essential to consider the impact on the calibration of your EFI or the jetting of your carburetor. More air means proportionally less fuel, and that means a lean mixture. Get it right before you run it hard, or it could overheat, stick valves or fry seals and potentially seize.

Slip-on mufflers do two things… well, actually they do one, and the second is a by-product. They provide less restriction for the exhaust gases, and are louder as a consequence, but a lot of people buy them just for the decibels. Pity. Without getting into an exhausting debate or discussion over exhaust, at least at this “stage,” suffice to say if you can see through the thing, it’ll work.

And that could be it. For some it is enough, but it doesn’t need to stop there—arguably it shouldn’t. Having gotten air in more quickly, and eased the path of the exhaust gases, it makes sense to make sure the fuel metering system is working as efficiently as possible. So you want to have a look at that—and there’s more to fuel systems than jetting and the recalibration of stock EFI modules.

This is where it starts to get contentious. There are many ways in which you can sort out carburetion—anything from a fistful of jets and an “’88 Sportster” needle, to high-dollar marginally useful Dyno Jet kits, to throwing it away and replacing it with a so-called high performance carb (of larger CV, butterfly or slide type) and you will find a lot of variation in the advice you’re given. In the end, your chosen path will typically come down to how much experience (and luck) you have tweaking carburetors, who you trust and how much money you’ve got.

Exhausts (beyond slip-on mufflers) are no less involved. Empirically, nothing much beats the overall boost of good 2-into-1 systems on FX and XL models and “true duals” on dressers—period. Thing is, the 2-into-1 is nowhere near stylish enough for most folks these days, with the possible exception of the newest one from Vance and Hines. Pity… since they don’t come much more balanced than both pipes exiting the same collector.

That’s the main stuff, but not everything because there’s a few other things you can do without taking any tools to the cases, and that’s mostly the goodies that light the mixture—and a good thing to do if you’ve gone to the trouble of fixing the carb.

As you’d expect, Screamin’ Eagle offers a range of ignition systems, both street-legal and “competition,” which better match the spark to the less restricted motor, while Crane’s Hi-4 and Dyna’s Dyna 2000 remain popular choices for those less concerned about their warranties, and they have an element of tunability built in so you can experiment. And if you’re going to play with ignition modules, why not coils? And why not plug leads?

Playing inside the engine under the “rules” of Stage One boils down to this: Re-bore the original barrels, or buy a set ready made and drop a pair of 1550 pistons in under the stock heads and bingo! You’ve got a Stage One 95-incher. Do the same to a new TC96 and you get a 103″. Tear the whole shebang apart and put longer stroke flywheels in and—guess what?—regardless of the displacement gained when it’s all over, you still have a Stage One engine.

Stage Two
From here on you’re more likely to need the assistance of a professional.

The first thing to do is to carry out all the Stage One “stuff’ that you want to do before you start, because they are the basis for the next round of modifications. There’s no point sticking hot cams in a strangled motor. By the same token, there’s no point getting carried away with the need for a Stage Two if you’ve not taken your bike to Stage One yet—you might be quite happy at first base.

Stage Two is largely about cams. At Stage One, you’ve already got the basic means to draw air/fuel into the motor and to get the gases out. The next step is more about how long you open the doors to let the fuel through, and how wide you open them, and when—which is (or should be) absolutely determined by what sort of work you want your bike to do.

There is probably more written on Harley cams that anything else about an engine build, and no shortage of people far better qualified to go through specifics. I’m just going through the general stuff so I can’t be blamed for your sticking something wholly unsuitable into your motor.

What’s unsuitable? Something that makes your bike less capable for the way you want to use it.

It is very much at odds with the traditional perception of tuning that you can have a Stage Two motor actually detuned compared to the original. But tuning isn’t only about power; it’s about suitability for the purpose. You could build a touring Buell, a hot rod bagger or a lazy Dyna Sport by judicious use of compression and cam profiles matched to an appropriate induction/exhaust system.

Cams are identified by lift, duration and angle… and quantity. Sportsters and Buells have four with a lobe apiece, one for each valve. Big Twins up to and including the Evo have one with four lobes that run all four valves, and Twin Cams have two with a pair of lobes each, one per cylinder.

There’s actually a fifth spec, which isn’t discussed much but should be, and that’s the ramp. A steep ramp takes the pushrod to the maximum lift very quickly, and returns it to rest as quickly as the spring can force it—as opposed to a gentle ramp which the cam follower will… well, follow. The reason it needs discussing, especially on single-cam Big Twins, is increa- sed valve and guide wear, as well as the nasty-stiff springs these things usually require. Aggressive ramps can really tear all that stuff up in short order.

A high-lift cam will let more fuel through but they are generally used on fast spinning motors—the high lift allowing a good lungful of fuel and air compensating for the need for a short duration to give the valve a chance to close again and be seated correctly before the next cycle starts. You don’t want to compress the fuel while the inlet port is open, because it’ll spit it back out again. If you’re playing with high-lift cams, you’re more likely to use stronger valve springs to get the valve shut quickly, but there is a trade-off in that the harder the spring is pushing against the valve-train, the greater the potential for wear of the cam, follower and bearings.

A long-duration cam will provide the maximum opportunity for the fuel/exhaust to get in or out, but shutting the valve late increases the chance of the valve being open on the compression cycle. They’re better suited to slower-spinning motors in conjunction with a lower lift.

The angle will determine when the valve starts to open, and there can be an overlap built in according to what the engine is to do. It is possible to open the inlet port a little before the piston has reached TDC to make sure that it has opened sufficiently when it starts to descend, drawing fuel through; it gets away with it because the exhaust port is wide open and provides the easier route through. Similarly the exhaust valve won’t quite have had time to shut before the piston descends, but by then the inlet valve will be wide open and it will draw it through there rather than the exhaust valve that is slamming shut.

The available profiles represent everything from mild to wild in their characteristics, but you don’t have to make your decision in a vacuum. Every combination has been tried by a very bright engine-builder, and whoever’s doing your cam installation work will probably be asking you a lot of questions about your riding style and expectations. If they’re not, be concerned. They may be good, but they’re not psychic and they need to know what you want.

Stage Three
There are those who would say that the first thing you should do to make a Harley work properly is to sort out the heads, but that is decidedly where “Stage Three” comes in.

Put politely, standard porting is not best suited to high performance. Harley engineers seem to be stuck on the notion of using exhaust ports as “governors,” since that’s the bottleneck to flow on virtually every V-Twin they make (except the V-Rod). This is where the experts come in, and you have to put yourself in their hands. Sure, you can buy heads, etc. and stick them on yourself, but when you’re that deep in, you’re not going to put those heads on without seriously considering what you want from the bike. Well, if you’ve got any sense you’re not.

You’re in big money country now and a half-cocked Stage Three will not be much better than an amateur Stage Two—certainly not worth the additional expense of the parts. Yes, I know you can get ported heads off the shelf, but ported for what? More torque or more horsepower? Higher or lower revs? Fuel efficiency or straight-line ability? Before you start you need to know where the power is needed, and what sort of power, to determine the size and shape of the valves. Until then it’s merely a technical exercise.

And it’s not just heads, whether bought or built—and that is why we now start to differentiate between mechanics and tuners. At Stage Three a motor really should be a blueprinted engine as well. It’s no longer enough that it is as good as an assembly line can make it; if you’re going to do it properly, it’s got to be as accurate as the original drawings: the blueprints. If the drawing has a dimension of 1.7701mm that’s what it has to be, not +/-0.005mm, but 1.7701… exactly!

A blueprinted engine will be less stressed than a production line example—even a good production line example—because everything will work as it was designed to work. The sort of engineer who will be capable of matching the specification will be more than capable of sorting out your porting, cam and carb requirements to make it better than the blueprint for your specific application, and that is the ultimate state of tune for your bike.

Stage Four
Anything goes. Turbos, blowers, nitrous, strokers, billet motors, massive monsters built for the purpose—from parts that have never seen a Bar & Shield logo.

Stage Four is the domain of the serious power addicts. Doubling the stock horsepower isn’t a challenge anymore. Tripling it would be good, though. You won’t see many of these bikes on the road because they’ll have sacrificed a lot of their rideability along the way—in fact some will be physically unrideable! But on a quarter-mile strip of tarmac, head-to-head with someone who thinks they know better, they will demonstrate just how much you can get out of an air-cooled V-twin motorcycle.

It doesn’t get any more sensible when you consider that it is perfectly possible to bolt an off-the-shelf turbocharger or supercharger to a stock motor, in which case it’s a Stage Four instantly! Don’t be surprised if this sort of instant Stage Four is “boosted” onto center stage in performance circles within the next couple of years either! As it gets harder for anyone to do anything to Harley engines legally (and it is getting harder), the aftermarket has already come up with at least one “wave of the future” power adder, in the form of the EPA-friendly inter-cooled Pro-Charger. (Imagine Stage Four power and no emissions or noise violations!) After all, in the absence of SEMA-type lobbying muscle to prevent it, no one should expect that things will be any easier or more legal than adding boost has been for the car guys, these last decades.

There’s one last thing you need to know: No matter what you’ve got it’ll never be enough, and the inescapable truth is that today’s Stage Four will be thrashed by tomorrow’s Stage Two, and the day after’s Stage One. Performance is transient, even in Harley circles.


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