[RXT]

An excellent post

I hope you do not mind if I add to this excellent post to explain the why of making power, and thus explain what parts contribute to making more power.

All engines make power by burning a proportionate amount of air and fuel. To make more power, you simply have to introduce more air and fuel. However there is one element often left out of the equation. That being the element of time. Horsepower is derived by how much air and fuel you can get into and burn in the engine, in a given time. This is where RPM comes to play. It's easy to understand. Your engine would theoretically burn twice the fuel at 6000rpm then it would at 3000rpm, thus making more power. But at twice the speed, the dynamics of the air flow entering the engine changes. At faster engine rpms, the valves which allow the air to enter the engine are opening and closing faster, and the amount of time they remain open is drastically reduced. Bends in the manifold or irregularities in the surface of the intake runners, create resistance to high speed air flow. And fuel can fall out of suspension, puddling on the walls of the intake runners.


To make hp, many performance modifications for gas engines are often designed around improving the breathing capability of the engine at higher rpms. For example, intake manifolds come in a variety of designs intended to improve breathing. Everything from using long runners, dual planes, or other designs which have larger diameter runners with as few bends as possible, enhance high speed breathing. Porting and polishing is an extension of the modified intake systems. By smoothing over the transition between the intake manifold and the head, the air flow is less interrupted, thus improving high speed air flow to the cylinders.

Cams are another component designed to improve breathing. By controlling the valves at higher engine rpms, an aftermarket performance cam can open the valves earlier, open them deeper (into the cylinder) and for a longer period of time. The aftermarket cam allows more time for more air to get into the cylinder. When it comes to getting more fuel in, there are numerous means to get in more fuel. In the carburetor days, having larger or multiple carbs was the way to get more fuel in. These days there is fuel injection and with fuel injection, the option is to increase the size of the injectors and increase the pressure at which the fuel is injected.

On the exhaust side, improvements to breathing can be made there too. Getting rid of the exhaust quickly and efficiently makes more room for the incoming charge of air and fuel. Everything else on the high performance engine is designed to supplement or add dependability at these higher rpms, such as performance ignition systems. Or even combustion chamber designs. Many performance engines can use multiple valves. There is also the classic and effective hemi design which benefits by it's use of very large diameter valves.

Most of these mods will increase power, but at higher rpms. Many of these mods do not enhance low rpm performance very much, if at all. Take the performance cam. While they allow more air, more time to enter the cylinder, at high rpms, at lower rpms or idle, they become inefficient. This is why you will notice a lopey idle with many high performance engines. It may sound cool, but they are actually running pretty poorly and probably burning extra fuel in the process.

Another means to increasing power is to increase displacement. Like anything else, a physically bigger engine, allows more air and more fuel to enter the cylinders to burn. A V8 for example, will always produce more hp than a 4 cylinder or six cylinder, simply by having a larger physical size.

Superchargers and turbochargers are just another way to increase the amount of air into the engine. They do require an increase in the delivery of fuel, but they can increase power substantially because they can force feed more air into the engine, than the engine can draw on it's own. This is the only true replacement for displacement. With supercharging or turbocharging, a smaller engine can indeed produce more hp than a naturally aspirated V8.

Power adders such as nitrous oxide, isn't a fuel in itself, but it does have qualities which increase hp by it's use. First, nitrous oxide has the ability to cool down the intake charge, a lot! Thus increasing the density of the incoming air, much like an intercooler does, on a turbo'ed engine. This increased density means more air enters the engine. Next, nitrous oxide contains oxygen which also burns with the fuel. It's simply adding more air into the engine for the fuel to burn with and releasing more power.

Besides nitrous oxide, plain old water can be a power adder. Water injection can be used to increase hp. It works similarly to nitrous, in that it cools the intake charge, increasing the density of the air entering the engine. Add more fuel and you make more power.

There are other types of fuels which naturally produce more power due to whats known as energy density. Diesel, for example contains almost twice the energy density of gasoline, per gallon. This is also why diesels tend to inherently produce greater torque and increased fuel economy at far less engine rpms. At the other end of the spectrum of fuels, you have nitromethane. Technically, engines that burn nitro, tend to be very high horsepower engines. Top fuel dragsters exclusively run on nitromethane, but the fuel itself has a very low energy density. The difference is, in a top fuel engine, you can burn over 7X the amount of fuel in the engine at once, thus releasing an enormous amount of power at the cost of horrendous fuel economy.

So in a nut shell. Making power is a matter of introducing as much air and fuel into the cylinders at higher rpms, as possible. Performance parts, such as "chips", physically cannot trick the computer enough to introduce increased amount of air and fuel into the engine to make a significant difference. Nor do other "bolt on" products which promise performance, like special spark plugs, or fuel line magnets.

Ed