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.

A. Gee, I’m not aware of any true dual exhaust systems on production cars these days. 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 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.

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, or am I looking at another afternoon in the driveway?

I don’t think they’re at fault here at all. 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, which you can spend an afternoon installing in the driveway.

But keep in mind, if those rotors warped in a year, your next set probably will not be any better.

So I’d ask your Honda dealer what kind of price he’d give you to install a set of factory rotors and pads. It seems like he’s being very nice to you. Or maybe you’ve berated him to the point where he’ll do almost anything to get rid of you now. But the factory rotors and pads definitely last longer, in our experience. So that’s your best long-term solution.

Well, that’s not true. Your best long-term solution would be to forget to return the loaner car!

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