1: The first option is to make your engine more efficient by tuning the air/fuel mixture, reduce intake and exhaust restrictions, decrease the rotating mass, increase ignition output, and tune engine timing. This is the purpose of most aftermarket power products, like high flow air filters, exhaust systems, high output ignition components, etc. The problem with these kinds of modifications is that performance gains can be small if not unnoticeable.
2: The second option is to increase the RPM of your engine. This is a very effective way to produce more power, but nothing comes easy. To spin at such high RPMs requires very high quality (and high-priced) engine parts that can withstand the abuse of the rapid rotation. Also, the increase in RPM substantially increases wear and tear on the engine resulting in decreased reliability and shorter engine life. Most stock Harleys have a red line RPM of around 5500 to 6000 RPM. Regularly revving your engine faster than the red line RPM is extremely risky without extensive engine modifications.
3: The third option is to increase engine cubic inches. Big engines burn more air/fuel, and hence, make more power per revolution. You can easily increase the size of the engine’s displacement by boring the cylinders and running a larger piston, or by lengthening the stroke of the crank, but you can only go so far before you’ve bored the entire cylinder away, or your piston is slamming into the cylinder head. Engine modifications of this type not only require extensive downtime, but can easily become extremely expensive.
4: The fourth option is to pack more air/fuel into the combustion chamber before igniting it. The result is the same as using a larger engine. The problem with this method is that it’s not as simple as telling your engine to suck in more air/fuel, it’s restricted by atmospheric pressure. At sea level, atmospheric pressure is 14.7 psi. This is a measure of how densely packed our atmosphere is with air molecules. Now imagine if you could trick mother nature by making atmospheric pressure 21psi. You’d be packing around 50% more air into your engine, which means you could burn 50% more fuel, meaning you’d be making approximately 50% more power. Supercharging is how it’s done. By utilizing this technique, a small engine can act like a big engine. That small engine is also more efficient because it has less weight an d rotating mass than a big engine.
The idea is simple – A supercharger (or blower) forces more air and fuel into the cylinders than can be naturally drawn into it by the pistons one each intake stroke. With or without a supercharger, there are a lot of factors that affect how much air/fuel mixture actually makes into the cylinder per stroke. This leads to the fact that no normally aspirated engine can achieve 100% volumetric efficiency, aside from some very rare cases with perfect intake conditions and only within a very narrow RPM range. A supercharger ensures that the cylinder is filled completely with air/fuel mixture so it can meet or exceed its full potential of 100% volumetric efficiency. This allows the engine to produce more torque and horse power though out the entire RPM range. Almost all performance products on the market today aim at improving your engines volumetric efficiency, NONE will show gains that a supercharger can produce.