Engines. Never has there been a more simple air pump built, modified, and blown up. Sure, we like to think of our engines as more than an air pump, but let's face it, it pulls air in and pushes air out. Now, the efficiency of that air pump-in this case, we will say the pump displaces 440 ci and is in a Road Runner-is directly related to how well the surrounding components allow that air to flow through the pump. If you have a small inlet (carburetor) that flows 650 cfm, the air pump is going to starve. Let's say you have a larger inlet, 850 cfm. It will not starve due to more intake volume, but what if the pump's outlet is not properly sized? Let's say your 440-inch air pump has an 850-cfm inlet, but each of the outlets is only 151/48-inch in diameter. Let's go even farther, and say each of these eight outlets travels and merges into a single 2-inch outlet that has bends and a noise suppression device in the mix. The pump will be able to bring in air, but not expel it. This will cause the pump to not be able to pull in a large amount of air, and hamper it pumping to its full capabilities. This problem is called backpressure.
When it comes to an exhaust system, backpressure typically reduces performance. Backpressure on the exhaust flow can help to reduce sound, but at the same time, it limits engine power. This power reduction comes from an inefficient burn in the combustion chamber, where spent exhaust gasses are backed up into the combustion chamber and contaminate the next burn cycle.
Another problem associated with backpressure is heat buildup. Heat builds up in the muffler, and then continues up through the entire exhaust system to the exhaust manifold and engine. This heat retention causes damage to the muffler, the system tubing, the manifold, and the gaskets. Even ignition wires can burn up due to an overheated, inefficient exhaust system.
Our Project M/Holley Road Runner has recently been the recipient of a new air pump. This air pump, built by Indy Cylinder Head, is rather large. The initial exhaust system featured a small "gas expulsion system" (exhaust), and definitely needed some upsizing. Since the car is in the capable hands of Musclecar Restorations in Chippewa Falls, Wisconsin, and they have a new state of the art Mustang chassis dynamometer, we decided to show you the effects. Thanks to Tube Technologies (tti), we were able to display the increase in horsepower by increasing air-pump efficiency.
Exhaustive Research
Choosing The Right Exhaust
Choosing the right muffler and exhaust system may seem like an easy task, and it is, provided you are honest with yourself about what your exhaust will need to be capable of. If you aren't sure about the parameters required, it can be one of the most power-robbing decisions you can make. the choice is so frustrating because of the variety of options available, and the fact that no one can ever agree on which muffler is the best.
Things to Consider
Is your motor going to have performance add-ons?
With a stock engine, it is advisable to keep the same size piping that came from the factory. If you choose a large diameter pipe in this application, a loss of low-end torque will occur. For a mild/moderate performance engine, a larger than factory size pipe will allow for better performance. Also look for a muffler that has great free flowing characteristics.
For a true performance engine, a true free flowing exhaust will be needed. It is best to contact the exhaust manufacturer and get their recommendations.
Will you have a crossover pipe?
For those running a true dual setup, a crossover pipe is also an option. An H-pipe or X-pipe is used to equalize the pressure in the pipes. Several tests have been done, and it is the consensus that a true X-pipe system will out perform a traditional H-pipe configuration.
Sounding Off
If you're running on the street, or in many racing series, you need mufflers. They also come in handy during long drives when the drone of the exhaust can be downright exhausting. But which muffler should you choose? It depends on your taste, your engine, and the space available on your vehicle. You also need to consider how you use that vehicle. A muffler can be used to tune your engine's power band so it makes more peak power (a good goal if you're drag racing or hitting the Autobahn), or more midrange torque (preferable if you're road racing or driving on the street). By its nature, a muffler also will have a profound impact on the way your vehicle sounds. Often, you can find several mufflers that provide comparable performance for your application, but one is quiet, one is loud, and yet another may be somewhere in between. Hi-performance mufflers offer some other advantages over stock units, as well. For starters, most high-performance models will last considerably longer, some even come with a lifetime or million-mile warranty. Performance mufflers can also improve your vehicle's fuel economy by helping the engine become more efficient.
A Sound Design
A muffler's purpose is to muffle the noise produced by the engine. When it comes to high-performance mufflers, there are essentially three designs: cancellation, absorption, and diffusion. A cancellation muffler features chambers inside, which tune and cancel various sound frequencies. An absorption muffler forces the exhaust to pass through a perforated tube that is wrapped in sound-deadening material. Various kinds of packing material are used to absorb sound, including fiberglass ("glasspack"), stainless steel mesh, and ceramic products. Absorption mufflers often feature a straight-through design. Some hybrid models, including "turbo muffler" designs, also use cancellation-style chambers to help muffle sound. A diffusion muffler uses diffuser plates at the muffler's end to split up the sound so it follows many different paths. Adding or subtracting diffuser plates can tune the sound coming out of this type of muffler. (Contrary to what you might imagine, you get a quieter exhaust system by running fewer discs.) Some hybrid diffuser mufflers also use absorption material to reduce decibel levels even further.
