A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

If you shove a potato in a car's tailpipe, will the car explode?

April 2, 1990

Dear Cecil:

Recently I was watching the season premiere of Against the Law (Fox TV) when a character mentioned that he had almost blown up his dad by sticking a potato up his car's tailpipe. Naturally I thought back to Beverly Hills Cop, where Eddie Murphy foiled the bumbling cops by putting a banana up their tailpipe. Does this really work? If so, why is it not more of a problem, especially in big cities where roving packs of thugs beat the tar out of people for fun? Seems like blowing up a car would have more comic value. Must the potato be cooked? Will any sizable fruit or vegetable (say, eggplant) do? I'd test on my own car, but it already dances on the thin line between minimal functioning and moribundity.

Cecil replies:

How many times do I have to tell you? Don't believe anything you see in the movies or on TV. Movies and TV shows are written by Hollywood scriptwriters. For scriptwriters, reality is basically a plot device. Stuffing a potato or anything short of a hand grenade up a car's tailpipe won't make it blow up. But it will keep the car from running. If exhaust gases can't escape, the engine can't "breathe," so it dies.

Think about it. When a car's cylinders move up and down, they pull fuel and air in and push exhaust gases out. If the tailpipe is blocked, the exhaust can't go anywhere and stays put in the cylinders, preventing fresh stuff from entering. No fresh stuff = no combustion = no transportation.

It also means no unintended explosions, which maybe is why street gangs haven't picked up on it. Thank God.

Blowing it out your tailpipe

Dear Cecil:

Your reply to Patrick O'Malley regarding the potato-in-the-tailpipe trick was, at best, only partially correct. When I was a mere sprat, my older brother and I heard rumors concerning the effects of a potato lodged in the tailpipe. Being good little experimentalists, we naturally had to determine the truth. So a choice spud from Mom's stash went into our retired neighbor's tailpipe (that is to say, his car's tailpipe), to await his next trip to the store.

The car neither exploded nor became immobilized. (Perhaps one of those wimpy imports people drive today would've conked, but this was the Fifties, when men were men and American cars kicked butt.) Instead, enough pressure was built up to eject the potato at high speed. Fortunately, our neighbor's driveway sloped up from the street, so the potato impacted asphalt within a few feet. Judging by the mashed potatoes left on the pavement, that tuber was traveling fast enough to take somebody's head off.

Pleased to be of service, keep up the good work.

Cecil replies:

It is all very well to talk about potato theory, G. But it's only through the efforts of bold pioneers such as you and your brother that real advances in potato science are made. Thanks.

Blowing it out your tailpipe, Part two

Dear Cecil:

Many years ago, when I was young and lived in a city far, far away, I was tempted to retaliate against my neighbor's Miata. Casting about for an innocuous form of annoyance, I chanced upon the old potato-in-the-tailpipe trick. Finding, like G. Hall, that one potato tended to be expelled from the tailpipe, I didn't quit. Rather, I just mashed four of the suckers in there. Success! Four was too much even for a Miata. Just trying to help those of a vengeful bent amongst your readers. Sign me …

Cecil replies:

Just proves the old saying, Spuds. If at first you don't succeed, get a bigger hammer.

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