Is David saving his carburetor or just annoying his wife?

Dear Car Talk

Dear Car Talk | Jul 01, 2011

Dear Tom and Ray:

I am writing to you to settle a disagreement that my dad and mom had when I was a kid (in the 1970s) and my wife and I have currently. Does an engine ever need to be floored (hard acceleration) to "blow out the carbon"? Was that merely an excuse for my dad to show off his 1967 Hemi Dart at stoplights? Or was there actual benefit for the hard acceleration once in a while? I use that same excuse with my wife at stoplights (in a much slower vehicle). Neither my mom nor my wife believes it has any benefit, and they think it would be just fine for the rpm to stay at or below 3,000 for the lifetime of the engine. What do you think?

-- David

RAY: I think I'm going to ruin your day, David. Because I have to break the news to you that your wife and mother are absolutely right.

TOM: In the '70s, cars had carburetors. Carburetors let gasoline slosh into the cylinders. And with all that excess gasoline, a buildup of carbon was a much more common problem.

RAY: There was a school of thought that suggested that running the car at high speed would help clean the caked-on carbon off the valves and pistons.

TOM: But by "running the car at high speed," they meant taking it on the highway for a long, high-speed drive -- not stomping on the gas at a stoplight and leaving a lime-green AMC Pacer in the dust.

RAY: Then there were some high- performance cars that had four-barrel carburetors. Two of the barrels opened up for normal, moderate-speed driving. And then, when you needed a lot of gas for high-speed driving or hard acceleration, the other two barrels opened up.

TOM: And if you never stepped on the gas hard enough to open up the two high-speed barrels, they could get gummed up and eventually fail to work. So that was another reason to "blow out" certain high-performance carbureted cars back in the day.

RAY: But cars haven't had carburetors since the 1980s, David. They all have fuel injection now, which meters the gasoline so precisely that carbon buildup on the pistons almost never is a problem. So neither of those old justifications for stomping on the gas holds water today.

TOM: Your wife and mother are correct. A modern car can spend its entire life never exceeding 3,000 rpm, and be completely happy and fulfilled -- mechanically, spiritually and emotionally.

RAY: In fact, stomping on the gas and making jackrabbit starts is terrible for the car. It shortens the car's life because of all the stress it puts on the drive-train components.

TOM: So it's time to catch up with the times, David. You're in for a little humiliation when you have to apologize to the women in your life. But don't worry -- you'll look good wearing those pants up around your chest ... mumbling "yes, dear."

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