If there is one thing, one aspect of a car that exemplifies Mustang ownership, it has to be the sound. No matter where you go, the supermarket, a car show, or just cruising down the road, when a Mustang passes by, you know what it is before you even see it. Sometimes you can hear a ripe Mustang from a mile away, that distinct throaty rumble that can only come from a Mustang. The 4.6L Mustangs have a good sound, but the 5.0s and 289s have a completely different tone that just screams “I am Mustang, you love me.” This is not by accident, and it certainly does not come factory. The factory exhaust has always been a little on the wimpy side, showing way too much restraint and much too quiet. No, the Mustang’s vocal coach is the aftermarket.
There are always different degrees of Mustang sound, from the subtle low rumble to the full-on drag race scream, but for the typical street Mustang, it is somewhere in the middle. The key to getting this sound comes from two things- pipe diameter and muffler style. There are three main types of performance muffler- chambered, turbo, and perforated mufflers. Restrictive mufflers, the kind the factory uses, basically bottlenecks the exhaust into smaller chambers. This increases backpressure to the engine, and muffles the sound. They quiet the exhaust at the expense of performance and tone.
Chambered– Chambered mufflers, such as Flowmasters, use internal walls and baffles to direct and redirect soundwaves. This creates cancellation of the wave, which reduces the sound. The volume and sound of the exhaust note can be tuned by the placement and size of these baffles. Chambered mufflers last forever (as long as they don’t rust out) because there is no fiberglass packing inside to burn up.
Perforated– the classic tube mufflers like Cherry Bombs, are perforated mufflers. These are also called “glasspacks”. These can be straight-thru design (tube mufflers) or use look like typical mufflers, in which the perforate tube snakes inside the can. The area around the perforated tube is packed with fiberglass or steel mesh to absorb the sound. Very little reflection and cancellation occurs in these mufflers, which makes them much louder, but also more annoying. They tend to “drone” or hum inside the car, and are less throaty than they are raspy. That is not always a bad thing, Cherry Bomb mufflers are cool. Eventually, the fiberglass burns up, and you are left with a really loud car.
Turbo– The “turbo” muffler is really a combination of the two. These mufflers use a perforated tube that may snake inside the can or be divided into several perf tubes that flow into chambered baffles. Typically, the entire muffler can is filled with absorbtion material (fiberglass or steel mesh). Where the name came from is anyone’s guess, but not all turbo mufflers are high-performance. Buying a no-name turbo muffler is a crap-shoot, so stick with the names you know, unless you can hear them for yourself. Unlike the connotation, you do not want to use a turbo muffler for a car with an actual turbo, this creates too much restriction for flow, which impedes the work of the turbo. For a turbo car, you want an unrestricted exhaust for maximum performance.
When it comes to mufflers, restriction is the key. You want the least restriction possible, while attenuating the sound. Too much backpressure kills the engine’s ability to flow, not enough backpressure is a bad thing too. That brings us to tubing. The diameter of your exhaust tubing is much more important than you may realize. A small diameter pipe, under 2”, creates a bottleneck, like trying to breathe through a straw. On the other hand, a large pipe, like 4” pipe, is too big (for moderate power cars, 500HP or less), not enough backpressure. Backpressure is your friend, the right amount of BP will actually help your engine bring more air and fuel into the combustion chamber. This is called scavenging, and it is a direct result of the pulse of the exhaust. As each pulse of gas exits the pipe, it creates a low-pressure area behind it. These low-pressure pulses create a vacuum inside the exhaust, sucking more air and fuel into the combustion chamber. A pipe that is too large minimizes the high-pressure pulse, which prevents the low-pressure pulse from forming. There are many factors at work here, but the diameter of the exhaust is directly related. For most street cars (250-400 horsepower engines) running dual exhaust pipes (one for each side) a diameter of 2.25 to 2.5-inches is sufficient to promote scavenging and yield a great tone, a larger pipe yields a lower tone (in most cases).
You could take your car to the local muffler shop and have a custom system installed, which would cost a pretty penny, or you could take on the project yourself, save some cash, and get the exhaust you want, not just whatever that shop sells. Installing your own exhaust system is not that difficult when you purchase a pre-bent kit like the one we picked up from Summit Racing. This does come with a caveat though, because not all kits are created equally. Some kits are custom fit, which means they are pre-bent, but not cut to length, you have to measure and cut the pipes yourself. This means a lot of fitting and trimming, under the car. You would not want to cut before actually putting the pipes under the car.
Other kits are pre-bent and pre-cut, like the one we used. That does not mean it will be perfect, but the kit we used fit quite well. Another consideration is how the pipes mate to each other. Most pre-bent kits come with clamps, to compress and lock the pipes together. These are simple and functional, but they don’t look very good. You can always clamp them together and weld them up later. Once you clamp the pipe, it won’t come apart, so keep that in mind.
We went the process of installing a new dual exhaust system on a 1965 Mustang coupe project car. This was originally a 6-cylinder, and the new 302 under the hood needed some pipes. We coupled the Summit Racing exhaust system to a set of new Hooker Super Comp headers. Headers typically make an exhaust install easier because there is no downpipe for the stock manifolds, the headers are already under the car, where the exhaust pipes begin. If you are running stock manifolds, shorty or mid-length headers, you will need to have an exhaust shop bend a downpipe for you. We managed to install this system in about two days, without a lift, so you should be able to make it happen in a single weekend.