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ed11563


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Car Talk - Exhausted
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Today: What's the Advantage of Having Two Tailpipes?

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Dear Car Talk

Aug 27, 2015 (Archives)

6 Comments

exhaust system

Dear Car Talk:

When I was a kid back in the late 1940s/early '50s, you had to have a dual exhaust system. I think most of the new cars that have two tailpipes use the "cat back" system, running the dual exhaust only from the catalytic converter back. My question is: Does the "cat back" system give any improvement in performance, or is it just to look cool? Also, do any production cars have a true dual exhaust system? I expect that a true dual exhaust would require two catalytic converters and would not be cost-effective.

-- John

Gee, I'm not aware of any true dual exhaust systems on production cars these days, John. At least, I haven't seen any in the shop since the Nixon administration.

The vast majority of cars you see with two tailpipes out back have what I'd call "faux dual exhaust." That does nothing to improve the car's performance. It improves the car's appearance, but doesn't make the car go any faster.

The theory behind real dual exhaust systems is sound: You send gasoline and air into a cylinder, it detonates, then you have to clear the exhaust gasses out of the cylinder. The faster you can get the exhaust out, the faster you can get a fresh charge of fuel and air in.

That's why engines with four, and even five, valves per cylinder are popular. With more valves, you can get more stuff in and out of a cylinder quickly.

Similarly, if you have two real exhaust pipes running all the way from the engine to the tailpipe (one each dedicated to one-bank cylinders), you can clear your exhaust more quickly, get your fresh charge in more quickly and get more power out of the engine.

But it is expensive. You need a complete second exhaust system, with its own a muffler, catalytic converter (or converters, in many cases) and every thing else. And it adds weight, which cuts into fuel economy.

That's why most manufacturers just go the cheaper and lighter way, splitting the tailpipe after the catalytic converter and muffler, and sending two tailpipes out the back of the car.

That does give the impression of performance. You see a car with two tailpipes, and subconsciously, you say to yourself, "Wow, that car must have a lot of power." But all it really has is five extra feet of tailpipe



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ed11563


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    Moparfool • 16 hours ago

    The Car Talk guy must be spending zero time in the shop now if he is unaware of any dual exhaust systems on cars these days.

    My 2009 Dodge Challenger R/T has true dual exhaust with two separate pipes and two cat converters.

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    Gigem85 • a day ago

    Not sure about the C4 Corvette, but Corvette has had true dual exhaust from 1997 (C5) through current. It has 2 cats and an H-pipe.

    My 69 Camaro with 396 has true dual exhaust the way we used to have them - headers and blown out turbo mufflers. It is not stock exhaust so not sure how the real exhaust was. My 72 Corvette 454 does have stock exhaust and it is true dual exhaust. Of course neither have cats and neither have an H-pipe or X-pipe.

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    George_San_Jose • 2 days ago

    In the hippie-era, late 60's, my car-knowledgeable buddies would tell me to install "headers" in my Ford Galaxy. I'd say "yeah, sounds cool". Actually I had no idea what the heck they were talking about .. lol ..

    BTW, there was a recent thread here on the Car Talk Forums about a new-ish Ford Mustang with an exhaust system problem, and I think the configuration of that vehicle as described by the OP was two separate exhaust manifolds, two cats, and two mufflers. Not sure if there was any criss-crossing between the two sides of the piping though.

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    Wes22 • 2 days ago

    Cars in the 50s did not have a catalytic converter. Most dual pipes ran from the exhaust manifold as my 1950 did. None that I know of were factory installed. About all the extras then were radio and heater. Wes

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    Look over there • 2 days ago

    Current Corvettes seem to have true dual exhausts. They have two mufflers and two catalytic converters. Though they do have four pipes.

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      Gigem85 Look over there • a day ago

      Not sure about the C4 Corvette, but C5 Corvettes had 2 cats and 2 mufflers with 2 tailpipes coming out of each muffler. The C6 and C7 Corvettes have a similar setup but if you have the dual mode exhaust there are valves in the mufflers that let some of the exhaust bypass a portion of the muffler for a louder sound - and better performance. With the dual mode exhaust Chevy claims an additional 5 hp.

      I think Corvettes should have a nice mellow but loud exhaust. My wife likes the quiet when on the highway. With the dual mode exhaust I put it in quiet mode on the highway and then in loud mode when in town so it sounds good. In quiet mode the exhaust opens up when revs get to something like 3,000 rpm for better performance.



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