Dear Tom and Ray:
I really like the look of the prominent chrome dual exhausts seen on so many cars and trucks these days. To me, they give a look of masculinity to the vehicle. For years, it seemed that manufacturers installed only single exhausts, except on the most powerful or sporty cars. And in many cases, the exhausts were hidden from view. Are "duals" now being installed more for looks, or do they really enhance performance, fuel mileage, etc.? Thanks. — Gary
Tom: Good question, Gary. Real dual exhausts will increase performance.
Ray: Here's the basic tutorial: Fresh gasoline and air go into the cylinders. It gets detonated by the spark plug, it combusts and then it turns into what? Exhaust.
Tom: And before you can send more fresh gasoline in there, you have to get that exhaust out. The faster you can get the old stuff out and the new stuff in, the better your engine "breathes," and the more power it can produce.
Ray: A lot of manufacturers have made their engines breathe better by adding more valves per cylinder — valves are the holes through which stuff enters and exits the cylinders.
Tom: But another way to improve breathing is to add an additional exhaust pipe. For instance, if you have a V-6 or V-8 engine, you can use one exhaust pipe to take the exhaust from just one bank of cylinders all the way to the back of the car. And you could have a second exhaust pipe for the other bank of cylinders. That gives you twice as much capacity to remove exhaust.
Ray: So it does work. But very few cars actually do it. More often, what you see are fake dual exhausts. There's actually a single exhaust pipe running from the engine to the muffler, and then the pipe is split, sending one tailpipe to each side of the car. That's just for looks.
Tom: Then there's the really cheap version, where the single exhaust pipe goes within inches of the rear bumper, then splits into two exhaust tips at the very end. Neither of those systems will affect performance. But I agree with you — they do enhance the look of a car and make it look more expensive.
Ray: Of course, the problem with a real dual exhaust system is that it is expensive — not only to manufacture, but to maintain. Think about it. When it rusts out, you'll need to buy two new exhaust systems. You'll be a hero at your local Midas Muffler. The guys'll have pinup posters of you in every bay.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)