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MGCCWDCC Logo Photos By Bob Vitrikas

What's Up with all the Dual Exhausts?

Have you noticed all the cars with dual exhausts lately? What’s up with that? Back in my youth, a car with dual exhausts was not a common site and when you did see one it usually meant it was a high performance model. Heck Oldsmobile (remember them?) even named their high performance model the 442, four barrel carburetor, four speed transmission and 2 (dual) exhausts. So why are there so many modern cars of rather mundane performance, sporting dual exhausts?  The answer is a bit complex but I’ll try to keep it simple.

An internal combustion engine is basically an air pump. The more air it pumps, the more power it makes.  There are three primary ways to increase the air flow; bigger engine displacement, increased air intake, and increased air outflow. For purposes of this discussion we’ll restrict our investigation to air outflow.

Dual exhausts allow less back pressure thus increasing air flow, thus increasing engine efficiency e.g., gas mileage and power. The bigger the engine displacement, the more important it is to move the exhaust gases out the tailpipe. Increasingly we are seeing the application of turbochargers in smaller displacement engines and here the exhaust flow is even more important since the exhaust gases are used to spin the turbocharger impeller.  Another way to increase exhaust flow is through increased exhaust pipe diameter but this can complicate routing of the exhaust through the various suspension bits such as the back axle.  In the case of a V-shaped engine such as V-6, V-8, V-12 etc. a dual exhaust makes the routing more convenient as well.  Dual exhausts reduce back pressure, allowing the engine to run cooler which means it’s not working as hard and thus has a longer life expectancy. One thing I’ve not seen written up but believe it is a valid consideration is that a dual exhaust can integrate two catalytic converters, doubling the ability of the engine to clean up the
tailpipe emissions.

On the other hand, compared to a single exhaust, a dual exhaust system is heavier and more expensive.  Dual exhaust systems tend to run cooler than a single exhaust and as a result more moisture can condense in the exhaust causing accelerated rusting of the exhaust components.

Simply put dual exhausts increase engine power and gas mileage while allowing the engine to run cooler thus increasing its life expectancy.  Duals also allow the use of two catalytic converters increasing the ability to reduce emissions.  And did I mention that dual exhausts look and sound really cool?  Simple eh? 


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