Here’s a basic fact about the internal combustion engine: Every single one of them is just a variation of an air pump. As the piston goes down with the valve open, air — mixed with fuel — rushes into the cylinder. As the piston goes up, it’s compressed, spark occurs, power is made, and the spent gases are sent merrily down the pipe. To make more power, we need to get more air in and out of the motor.
“More air means more power” is the mantra for this blog post and the easiest place to show this is with the air cleaner assembly. Mother Harley is handcuffed by EPA regulations, but we can let loose of a few ponies by simply changing to a good quality air cleaner assembly The Hypercharger comes immediately to mind, as does the Forcewinder or the Revtech free-flowing air cleaner.
The less restrictive air cleaner allows more air and fuel (more air requires more fuel) into the cylinder, giving us our power increase. One thing to keep in mind: Any time you change the airflow through an engine, the carb (or EFI) must be rejetted or recalibrated.
Next on the agenda are exhaust systems. Now that we’re getting more in, our next objective is to get more out. I know that drag pipes are popular, but the fact is, they actually hinder performance. They work at the rpm for which they are tuned and kill power everywhere else. This can be remedied by adding baffles and reversion cones such as AR Power Cones, but these still aren’t as effective as other systems.
The best choices for making power are the 2-into-1 header systems such as the Thunderheader, or the Vance & Hines Pro pipe or a D&D FatKat. If you don’t care for the looks of this style system, excellent results can be had with the Bub series of pipes, or the exceptional look offered by Kuryakyns Perfect Storm. An interesting development in today’s exhaust technology is the double-wall constructed Double D’s — pipes that should be very blue resistant. By the way, improper jetting or timing is the primary cause of exhaust bluing. Being too rich is as bad as being too lean (and yes, there is a product out there to remove this called Blueaway).
Up next — if the pocketbook permits it — is a carburetor change. On Evo’s 90 and up, the stock carb is a CV Keihin. This is a great carb if it’s set up correctly. Its outstanding low-end performance is offset by its small size and wimpy top-end pizzazz. This works well around town but suffers in the big roll-ons on the Highway. By far one of the most popular parts sold are the complete S&S Super E kits . Once again “more air, more power.”
These American-made kits are easy to install and come with an outstanding instruction booklet. Another carb to consider is the HSR 42 Mikuni. A strong performer in its own right, it also comes with detailed instructions. Both kits offer well-designed free-flowing air cleaners. The traditional S&S teardrop was developed to increase airflow due to a vane cast into the cover. And as a bonus, it’s good looking, too! The only improvement I would recommend is to replace the foam element that is supplied in the kit with one of the K&N gauze-type elements . The Mikuni comes with the K&N-style filter. I like both of these and have no preference either way.
For you EFI guys out there, K&N — in conjunction with the fine folks at Dynojet — have developed the Power Commander. This little unit allows you to make whatever tuning changes required after changing pipes or other modifications. Well engineered, this unit is infinitely adjustable and user friendly.
As we discovered early last week, we can add Kuryakyn to the list of performance enhancers in the EFI market. Their combination of exhaust, air cleaner and TTS system is a great way to upgrade your stock EFI Harley and make great gains with a relatively short amount of money.