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Car Talk: Advantage to having 2 tailpipes?

Dear Car Talk: When I was a kid back in the late 1940s and 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. Does the “cat back” system give any improvement in performance? – John

A: The vast majority of cars you see with two tailpipes 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 everything 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.

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Dear Car Talk: My 2003 Honda CR-V recently was part of a recall involving the air bags. Due to the risk of injury or death, I left my CR-V at a local dealership, and they provided me with a loaner while they waited for the replacement parts to come in. During that time, my CR-V sat outside in the rain and snow without being driven for two months. When I picked it up after they repaired the air bags, there was rust on the brakes, which they said would wear off quickly. However, the rotors also feel warped and vibrate heavily when I brake. They’ve offered to resurface the pads and rotors for about half the normal price (still $100 front and $100 back), but I don’t think I should have to pay for it at all. I just replaced all the pads and rotors myself last year, and it would be cheaper for me to completely replace them again. Should they take care of this for free? – Galen

A: I don’t think they’re at fault here at all, Galen. Nothing about sitting in a parking lot (even in rain and snow) would make the rotors warp or the pads wear out. Brake rotors do get rust on them when they sit. But your dealer is correct that the rust is quickly scraped off by the pads when you drive the car. So I’m guessing you bought real cheap rotors last year, not the Honda ones.

So if the rotors really are warped, you can try complaining to the people who sold them to you. If you’re lucky, they’ll stand behind them and give you another set. But keep in mind: If those rotors warped in a year, your next set probably won’t be any better.

So I’d ask your dealer what kind of price he’d give you to install factory rotors and pads, which definitely would last longer.