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Friday, 2 October 2015

How Can I Make My Stock Exhaust Sound Deeper?

How Can I Make My Stock Exhaust Sound Deeper?

There was a time back in the 1980s when auto enthusiasts were all but certain that doom was on the horizon. The rise of emissions equipment, computer controls and whispers of "sealed engine bays" were believed to herald the end of hot-rodding and customization forever. But a funny thing happened on the way to the 21st century -- namely, exactly the opposite. Since the turn of the century, horsepower and hot rods have seen a rise in popularity not known since the muscle-car era. Today, engines are more powerful, cars are faster and more sophisticated, and getting just the right sound is more important than ever before.

Mufflers and Cat-Backs
This is the default solution for many seeking a bit more bass from their ride, and for good reason. Cat-backs are complete replacement exhaust systems that bolt onto the back of the catalytic converter, preserving emissions compliance while enhancing sound. They're often relatively easy to install, and there are a plethora of options available from many manufacturers for most remotely popular applications. Muffler replacements are even simpler, and generally good for a bit of extra rumble. Cat-back systems can add some power too, depending on how restrictive the stock exhaust system was, and how restrictive the upstream exhaust and intake are. But they're almost always guaranteed to deliver some extra volume and a deeper tone. Before making any other major changes, shop around for a cat-back system or new muffler to see if there's one to suit your needs. "Chambered" mufflers typically offer a deeper note than non-chambered mufflers.

Cutting the Pipe
If you want a bit of extra sound without spending any money at all, you can do it with a grinder and a 1/4-inch thick grinding wheel. Start by crawling under the vehicle, and find the exhaust tube where it goes into the muffler. It's usually quite accessible, but use caution if you're working near the fuel tank. Mark out a spot on the tube about two inches from the muffler, and use the grinder to cut a slit in the bottom of the tube. You'll want to cut across the bottom of the tube, about a quarter of the way around its circumference. Start the engine, and walk around the vehicle while someone revs it up, so you can hear how it sounds. If you want it a bit deeper, you can widen the cut to about a third of the pipe's circumference. Additional cuts, spaced about four inches apart, will add depth and volume to the sound. This approach does have its limitations, but it's definitely cheap.

Straighter, Smoother, Larger-Diameter Tubing
The pipe-cutting trick is a good backyard hack for fine-tuning, but you can only take it so far before annoying, high-frequency noise starts escaping the tube, overwhelming the pleasant low-frequency soundwaves you're after. One way to decrease the emission of high-frequency waves is to decrease backpressure with larger diameter tubing. High-frequency waves travel well through dense, pressurized air; low-pressure soundwaves continue to fare well when system pressure drops. That's why high-performance, high-flow exhaust systems naturally sound lower than their lower-flowing, higher-pressure counterparts. Low-frequency waves are also physically longer, so long, straight sections of tubing will typically give a lower sound than tubing with a lot of hard bends. Always use smooth, mandrel-bent tubing; it flows better, and low-frequency soundwaves have an easier time navigating the smooth turns.

Tuning for Sound
Exhaust resonators are a well-known tool for tuning sound without muffling it too much. "Helmholtz resonators" use a length of tubing inside that captures certain unpleasant wavelengths, causing them to cancel out on each other. These can work well to fine-tune pitch, but they're tuned to specific engines and exhaust notes. The same resonator may not affect sound the same way on two different engines. However, you can emulate the effect by installing one or a two six-inch-long "cherry bomb" mufflers in the exhaust system about six inches past your catalytic converter. These shorty mufflers will catch the rapidly bouncing high-frequency waves, while leaving the longer, deeper waves relatively unaffected. This early cancellation also helps to reduce exhaust drone, or pipe vibration due to high-frequency tubing vibration. Thicker tubing, or wrapping the tubing in header wrap can have the same effect, if you don't mind the weight or aggravation.

Further Up
Obviously, eliminating the catalytic converter will open up a whole new realm of possibilities as far as sound is concerned, but it's also completely illegal if your vehicle originally came with a converter. Switching to an aftermarket, high-flow, metal-core converter will make a big difference in sound if you've already done work to the cat-back portion of the system -- especially if you started out with an ancient lead-pellet-style converter. Check for legality regarding the retrofit, though. Assuming you've already worked on the rest of the system, a set of full-length headers using long merge collectors will get your engine sounding about as deep as it ever will, for the same reasons mentioned in Section 3. For a given header primary tube length, the larger diameter and straighter the tubes, the deeper the sound should be. Equal-length headers are always best for performance; but, if you're going for sound, straighter header tubes should offer better low-frequency sound transmission.

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