For a hot rodder or racer, a rat engine is a big-block Chevrolet V-8. Powerful and beautifully designed, how did this well-respected engine get the nickname “rat”?

From James Cagney’s famous line “…that treacherous dirty rat” to the much-maligned rat nutters of the 1950s, calling someone or something a rat is the ultimate insult. When something is old, worn and falling apart, it is “shabby”.

So it’s somewhat surprising that the big Chevy earned the nickname rat.

In the early 1960s, long before the introduction of the first rat engine, a David and Goliath showdown was taking place on the nation’s race tracks. The Chrysler Hemi had become the dominant force in the Top Fuel and Top Gas categories, gradually replacing the Cadillac, Lincoln, and Oldsmobile engines that previously controlled these categories.

While the Chrysler Hemi produced loads of power, it was also physically larger and heavier than other V-8s. The massive engine quickly earned the nickname the Elephant engine due to its size. An elephant engine with a GMC supercharger looked huge when installed in the typical tube frame dragster chassis.

Although big elephants became the de facto standard in Top Fuel, there was another engine that could hold its own against the Hemi. Many teams took a different approach and chose the legendary small-block Chevy to power their dragsters. Most of the time, they didn’t bother with a supercharger, preferring a simple set of injectors.

On paper it was an unequal contest. The busted hemi was so much more powerful than the little Chevy, and it seemed like the Chevy had no prayer against the Chrysler in a quarter-mile run.

However, the tire technology of the day was in favor of Chevy’s rails.

While the big elephant engines put out a lot of horsepower, the tires of the day weren’t up to the task of bringing that power to the track. Much of that power went up in smoke, as Chrysler’s big rails burned the tires over almost the entire length of the trailing tip.

The little Chevies could also burn their tires, but their lower power allowed the tires to hook up and gain traction while the big hemis kept spinning their wheels. The combination of less wheel slip, lighter overall weight, and higher RPM allowed small Chevy-powered cars to give elephant-powered cars a run for their money.

While the hemi teams weren’t really afraid of the little Chevy dragsters, the small blocks tended to make them more than a little nervous. It wasn’t embarrassing to lose to a blown-up hemi machine, but it was embarrassing to lose to a fuel-injected Chevy.

Someone remembered the fable that the only creatures elephants are afraid of are mice, and started referring to little Chevy as the mouse engine. Therefore, the elephant and mouse engines competed for racing honors at race tracks across the country.

The mouse engine’s role as an elephant killer did not last long. Tire and clutch technology continued to improve, and the big elephants were finally able to deliver more power to the track. By the early sixties the mouse engine could no longer affect the big Chryslers in the Top Eliminator ranks. The small-block Chevy was still very popular in the altered, gas coupe, and modified classes. Although it was rarely raced against the big elephant engines anymore, the engine was still known as the mouse engine.

During that period, Chevrolet and General Motors followed a strict no-compete policy. It is well known that some GMs circumvented the official stance by supplying parts and technical help to racers without management’s knowledge.

Legend has it that in the early 1960s certain Chevy race cars showed up at various race tracks with a strange new engine under the hood. It wasn’t a mouse engine, and it wasn’t the big 409 V-8 that the Beach Boys immortalized in song. It was a mysterious, brand new Chevy V-8.

The mystery only lasted a short time, as Chevrolet announced a new big-block V8 in 1965. First available as a 396-cubic-inch version, the engine eventually evolved to 402, 427, 454 CI displacements. GM even offered a monstrous 572 CI version of the engine.

After the engine was introduced, many people continued to refer to it as the mystery engine. When the valve covers were removed, hot rodders began calling it the Porcupine V8 because, unlike the Mouse engine, which had the valve stems lined up in a neat row, the new engine’s valves were tilted at various angles.

Other racers noted that while the engine wasn’t a true hemisperical design, it wasn’t exactly a wedge head either. Thus, the engine gained another name – the semi-hemi.

Look at photos of Chevrolet race cars from the era and you’ll find plenty of examples of cars with the terms Mystery Engine or Semi Hemi painted on the hood.

For most rodders and racers, though, there was only one legitimate moniker for the new engine. If the little Chevy V-8 was a mouse engine, its bigger, more powerful, fiercer brother could only be a RAT engine.

The name has stuck. Today only old school fans and nostalgia fans still use the terms mouse and elephant engine. However, the name rat motor is still widely used to describe the big block Chevy V8. Far from being a derogatory term, the expression rat engine is popular with Chevy fans and is used as a title of respect for those who build and race other makes.

And that’s how the Chevy V-8 became known as a rat engine.