From our "arrested adolescence" department: how to make a old car fart.

Dear Car Talk

Dear Car Talk | Mar 01, 2008

Dear Tom and Ray:

Back in the 1960s, when I was an adolescent male, one of my friends told me that he could get his old car (late-1940s- or early-1950s-era) to "fart" whenever he liked. When I expressed skepticism about this claim, he demonstrated the phenomenon several times. By switching the ignition on and off while manipulating the foot pedals, he could make the car backfire with a spectacular farting sound that attracted the awe and admiration of any adolescents in the vicinity. I still don't understand how he accomplished this impressive feat, however. Can you explain the mechanics of "car farting" for arrested adolescents like me? -- Bill

RAY: Sure, Bill. How did you know we'd be the people to ask?

TOM: Before we explain how it's done, let me assure any parents of adolescent boys out there that this won't work nowadays. It only works on carbureted cars, and every single car made now is fuel-injected.

RAY: What your friend was doing was causing a backfire, Bill. We called it "banging." When you turned the key off in an old car (before fuel injection, and before steering-wheel locks!), the carburetor would continue to allow gasoline to pour into the cylinders.

TOM: That gasoline didn't get combusted, because the spark plugs weren't firing, so it got pushed out into the exhaust system, where it basically sat there, waiting for something to happen.

RAY: When you turned the ignition back on, that first spark would ignite not only the fuel in the cylinder, but all of the fuel sitting in the exhaust system too. And, kaboom!

TOM: We have a friend, whom we won't name, but Tony had a job during college returning rental cars to the airport in Boston. To get to the airport, you had to drive through a tunnel.

RAY: And Tony H., the friend we won't name, knew how to make the cars backfire. He found it particularly satisfying to "bang" the returning rental cars in the tunnel, where they made a tremendous noise.

TOM: He also discovered, to his chagrin, that when he "banged" a Rambler, which was one of the cars in the rental fleet, not only did it make an impressive noise, but sometimes it blew the entire muffler right off!

RAY: So he would pull into the rental lot with the car sounding like a Gatling gun, and the supervisor would say: "What the heck happened, Tony? Another bad muffler?" And Tony would say "Yeah. What a piece of junk, huh?"

TOM: So if anyone from Hertz wants to get in touch with Tony now to seek redress, let us know. We know how to reach him.

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