The Holy Trinity of bike tuning: pipe, air filter and fuel management.
Housed inside this bottle are ravenous horses that are unleashed at the push of a button.
Exhaust gases power a turbine that sucks in fresh air and forces it back to the intake system-simple, yet highly effective for big horsepower.
A serious airbox is necessary to withstand the pressurized air being pumped into it from the turbo. Billet aluminum does the trick quite nicely.
Big horsepower numbers always look impressive on paper, but they don't necessarily indicate the best performance for a particular application. A 12-inch stretched Hayabusa with 400 turboed horsepower will work flawlessly at the strip, but on a twisty bit of road or track it'll likely be left in the dust by a 600cc sportbike with a squirt of nitrous-application is as important as the cold, hard numbers. SSB examines the various potent possibilities for making your ride rip.
Pipe, air filter and fuel-management system
In the truest sense of a bolt-on power adder, a full exhaust system, air filter and fuel-management box (or a jet kit back in the day for carbs) have been the standard go-to mods for nearly every ride on the road. Better looks, lighter weight and increased power are the benefits, and there isn't much more that needs to be done after installation.
The reason a freer-flowing exhaust gains power is because it eliminates the noise- and emissions-reducing muffler (that also is quite heavy) and allows the engine to move more spent gas quicker. The accompanying fuel-management box provides the necessary adjustment to the fuel injectors and airflow to work with the freer-flowing exhaust as well as the improved intake airflow from the aftermarket air filter.
A custom dyno tune is always beneficial, but a lot of the downloadable preprogrammed maps will suffice and help achieve power gains if dyno tuning isn't available or in the budget.
Power delivery is most noticeable with improvements in the midrange and top end. Gains range from 5-15 horsepower generally.
Best Application: Street rider desiring better looks, sound and performance.
Average expense: About $1500 for parts.
Nitrous is a highly debated mod because when improperly installed it can end in catastrophe, and stock engine components won't tolerate the increased heat of an extended nitrous spray for very long. This makes it ideal for delivery in quick bursts or only during full throttle (like during a quarter-mile run).
Essentially, a nitrous system adds a highly combustible gas (nitrous oxide) into the combustion chamber with more fuel and air to produce more power.
Power delivery typically comes as an instant rush at the press of a button or upon reaching full throttle (depending on set-up). Gains typically range from 20-80 horsepower.
Best Application: Street rider desiring increased performance and the dragstrip enthusiast.
Average expense: $1000 for parts and installation.
Engine internals aren't something that a "do-it-yourselfer" will be able to manage in his garage-only a qualified engine builder should be consulted. The range of tuning is vast, and can be as minor as a ported head to a big-bore kit (making the actual cylinder heads larger to host larger pistons).
According to Yamaha tuner Chuck Graves: "Modifying an engine for more power is all about optimizing pressure, and an engine can be thought of like a pump. During peak power the pressure and leverage on the connecting rods needs to be optimized. The length of the stroke, the shape and size of the combustion chamber and the shape of the piston all determine how well the 'bang' is utilized. Of course, valves and ignition timing come into play as well, but each component needs to complement the other for maximum efficiency and power.
"Newer sportbike cylinder heads and valves are excellent, and a port job and valves won't offer gains like it used to. For big power the old saying still applies-there's no replacement for displacement."
Head porting makes the intake and exhaust surfaces smoother (and larger) so that less turbulence is created and allows the air/fuel mixture to move faster. A port job would typically be accompanied by a larger cam (responsible for opening and closing the intake and exhaust valves). Obviously a larger cam will allow the valves to open slightly longer-permitting more intake and exhaust to flow.
If you want to make big numbers on the dyno you'll need big displacement, as Graves suggested. All modern four-stroke motorcycle engines are oversquare-the bore (cylinder diameter) is larger than the stroke (distance the piston travels in the cylinder) is in length. If you're after more low-down torque you would increase the stroke for more leverage on the crank, while making the bore bigger and keeping the stock stroke will offer more overall horsepower with a possible loss of bottom-end torque. Obviously the two combined will make even more impressive power, but reliability comes into play because the cylinder head loses strength and the ability to effectively dissipate heat as these modifications are made.
One thing to consider is that the wilder the build (larger pistons, cams, etc.), the more expensive and less reliable the engine becomes.
Power delivery is smooth and linear throughout the rev range. Gains can range from 3 (mild tune) to 30 (big-bore kit) horsepower.
Best Application: Racing and competitive applications.
Average expense: $500-$5000.
Lately we've seen loads of fat-tire customs sporting a turbo system, but generally this is more of a bragging device than an applied application. Occasionally the bikes are so overweight that they require a turbo simply to help them lumber down the road, however.
For the most part, turbochargers are saved for the dragstrip racer or top-speed shootout competitor because of the violent top-end power and massive power gains; roadracers would typically struggle with the abrupt variations in power delivery.
At its most basic level, a turbocharger simply uses exhaust gas to compress outside air that's then channeled into a highly pressurized airbox and forced into the intake system. Obviously, more fuel must be paired to the increased amount of compressed oxygen.
Power delivery is violent and typically kicks in toward the upper rev range as the turbo spools up. Gains of 100-400 horsepower (when combined with support mods) can be expected.
Drag racers and competitive applications are ideal, but some street riders run low-horsepower systems for style and performance.
**Average expense: $3500-$6000 parts and installation.