Horsin’ Around

Learn how to gain horsepower in both your ride, and the system in it.

There are some things that just naturally go together. Combinations like ice cream and apple pie and peanut butter and jelly come to mind. As far as I am concerned, there’s another natural combination — high performance car sound systems and high performance cars. I believe that in a lot of cases, the same personality trait that causes an individual to long for more performance in an audio system is the same mentality that drives them to more driving performance. Sure the world is full of folks that will always be satisfied with a factory stereo and an ordinary engine. But there’s that small percentage of us (yes, I count myself among the small percentage) that just need more performance than the average guy or that’s never satisfied.

There are so many things that draw parallels between the two interests: High G forces vs high SPL, extra horsepower and large powerful amplifiers, fancy wheels vs exotic woofer cabinets, loud engines vs loud music, underhood dress up kits vs high tech wiring kits. Let’s face it, it’s no secret that most serious CAR SOUND & PERFORMANCE readers don’t have ordinary cars any more than they have ordinary stereos. One of the things that I cannot overlook is the similarity in what it takes to break out of the ordinary and enjoy a higher level of performance in both interests. Any good stereo worth having needs two things — lots of power and lots of displacement. Large speakers provide lots of air displacement, and big amps hooked to high capacity charging systems provide the power to get things moving. Most audio folks cannot ever feel that their system is “finished” and are always looking to increase either of these parameters. Imagine an autosound competition held at a drag strip where the SQ contest scores had the added element of 1/4-mile ET and MPH factored in. Now that would be exciting!

Interestingly enough, increased driving performance in a car almost always requires more power. And the factor that’s at the core of this parameter is similar to performance in an audio system. An engine, like a speaker, is really nothing more than an air pump. For an engine to perform, it must do the same thing as a speaker — displace air. With a speaker, the more air moved, the more SPL, and with an engine, the more air moved, the more horsepower. To get an idea of just how much air has to be moved, consider this fact: a 350-cubic-inch engine (5.8 liter) turning at 6000 RPM for one minute will attempt to displace a total of 600 cubic feet of air. Of course engines aren’t perfect, and because of pumping losses they don’t actually displace as much air as their displacement would dictate. A typical normally aspirated engine will not achieve more than about 85 percent pumping efficiency, which would equate to about 500 CFM of air.

Of course, pumping air alone will not result in any power. Some sort of fuel has to be included in the process, but, in an engine, the ratio of fuel to air follows a set of well-defined parameters. There are calculations known as brake specific fuel consumption (BSFC) that determine just how much power is produced with a given amount of fuel and the resultant air mixture. If we want to produce more horsepower, we have no choice but to pump more air in order to burn more fuel. There are two popular ways to increase power. We can increase the size of the engine or we can speed up the pumping process with higher RPM. Higher RPM will pump more air, but, like a speaker that gets more nonlinear with increased excursion, an engine gets less efficient at higher speeds. The air has less time to fill the cylinder and the pumping losses increase with increasing RPM’s.

No matter what the engine design, any attempt to increase horsepower requires an increase in air moved. Any modification that improves the engine’s ability to breathe can result in more power. The intake system, including, but not limited to, the air filter, throttle body, and intake manifold can all restrict the flow of air to the engine. Likewise, any mod that increases the ability of the engine to exhaust air can result in more power. This would include, but would not be limited to, manifolds, converters, and mufflers. However, in most engines, the greatest hindrance to air flow is the heads. No matter what the design of the engine, the valve/head area is the place where the engine suffers the greatest restriction. Accordingly, improvements in this area can result in great performance gains. Anything that increases the ability of the valves to flow better, such as porting, larger valves, or a bigger cam, can really make for impressive horsepower gains.

Of course with engines, there are other alternatives to improved air movement just like there are with speakers. Even though it’s the cone of the speaker that moves air, there are ways to “cheat.” In audio, we can add ports or horns to the actual speaker and move more air than simple displacement calculations would indicate. One of the most popular ways to cheat on simple displacement calculations of an engine is to use a device to force more air into the engine. The best methods to do this are with the use of a supercharger or turbo. Personally, I happen to be a fan of the turbo approach, but either can achieve similar results. If a turbo is used, a typical engine can actually exceed 100 percent volumetric efficiency. By this, we mean that the cylinder can actually be filled with more than 100 percent of the air that would normally fill it at atmospheric pressure. Forced induction, as it’s called, is a good approach for several reasons. Perhaps the greatest of these is that a relatively small engine can be used for most driving, and only when high performance is needed does the engine actually become “bigger and more efficient.”

Of course, like an audio system, the ability to move more air in an engine cannot produce performance gains by themselves. Improved fuel management control, accurate sensors, and proper programming are critical to increased usable performance. But, when all the details fall into place in a well executed system, the power gains can be phenomenal and will add to the enjoyment of not only the car, but the stereo as well.